Amines, proteins, digestion, sources and

Proteins

1. PROTEINS
Elton John D. Delos Santos, MAEd, MAN, RN

2. Section 20.4
Chiralityand Amino Acids
Return to TOC
20.1Characteristics of proteins
20.2Amino acids: The building blocks for
proteins
20.3Essential amino acids
20.4Chirality and amino acids
20.5Acid–base properties of amino acids
20.6Cysteine: A chemically unique amino acid
20.7Peptides
20.8Biochemically important small peptides
20.9General structural characteristics of proteins
20.10 Primary structure of proteins

3. 20.11 Secondary structure of proteins
20.12 Tertiary structure of proteins
20.13 Quaternary structure of proteins
20.14 Protein hydrolysis
20.15 Protein denaturation
20.16 Protein classification based on shape
20.17 Protein classification based on function
20.18 Glycoproteins
20.19 Lipoproteins

4. Amino Acids

5. Amino Acids
•Contain both an amino (—NH
2) and a carboxyl
(—COOH) group
▫-amino acids: Amino acids in which the amino
group and the carboxyl group are attached to the
-carbon atom
Side chains (R) -Vary in size, shape, charge,
acidity, functional groups present, hydrogen-
bonding ability, and chemical reactivity
▫>700 amino acids are known

6. Standard Amino Acids
•20 -amino acids normally found in proteins
•Divided based on the properties of R-groups
▫Nonpolar amino acids: Contain one amino
group, one carboxyl group, and a nonpolar side
chain
Hydrophobic -Not attracted to water molecules
Found in the interior of proteins, where there is no
polarity
▫Polar amino acids -Hydrophilic
Types -Polar neutral, polar acidic, and polar basic

10. Section 20.4
Chiralityand Amino Acids
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Abbreviations and symbols for
commonly occurring amino acids

11. Section 20.4
Chiralityand Amino Acids
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ESSENTIAL AMINO ACIDS
Nonessential Essential
Alanine Arginine* c.e.
Asparagine Histidine* c.e.
Aspartate Valine
Cysteine* Lysine
Glutamate Isoleucine
Glutamine Leucine
Glycine Phenylalanine
Proline Methionine
Serine Threonine
Tyrosine * Tryptophan

12. Section 20.2
Amino Acids: The Building Blocks for Proteins
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Polar Amino Acids
•Polar neutral: Contain polar but neutral side
chains
–Six amino acids belong to this category
•Polar acidic: Contain a carboxyl group as part
of the side chains
–Two amino acids belong to this category
•Polar basic: Contain an amino group as part of
the side chain
–Three amino acids belong to this category

13. Section 20.2
Amino Acids: The Building Blocks for Proteins
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Amino acids are organic compounds that contain a
_____ group and a _____ group and are found in
proteins as _____.
a.hydroxy; carboxyl; -hydroxy amino acids
b.amino; carboxyl; -amino acids
c.amino; carboxyl; beta amino acids
d.hydroxy; carboxyl; beta hydroxy amino acids

14. Section 20.2
Amino Acids: The Building Blocks for Proteins
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•Standard amino acids needed for protein
synthesis and must be obtained from dietary
sources
–Types of dietary proteins -Complete, incomplete,
and complementary
Essential Amino Acids
Arginine* Methionine
Histidine Phenylalanine
Isoleucine Threonine
Leucine Tryptophan
Lysine Valine
*Not essential
for adults but is
required for
growth in
children

15. Section 20.2
Amino Acids: The Building Blocks for Proteins
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Incomplete dietary proteins contain inadequate
amounts of:
a.one or more essential amino acids.
b.one or more nonessential amino acids.
c.at least one essential and one nonessential
amino acid.
d.none of the above.

16. Section 20.2
Amino Acids: The Building Blocks for Proteins
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•Four different groups are attached to the -
carbon atom in all of the standard amino acids
–Exception: In glycine, the R-group is hydrogen
•19 of the 20 standard amino acids contain a
chiral center
–Molecules with chiral centers exhibit enantiomerism
(left-and right-handed forms)

17. Section 20.2
Amino Acids: The Building Blocks for Proteins
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•Amino acids found in nature and in proteins are
ʟ isomers
–Exceptions: Some bacteria
–Monosaccharides prefer ᴅ isomers
•Rules for drawing Fischer projection formulas for
amino acid structures
–—COOH group is placed at the top of the projection
formula

18. Section 20.4
Chiralityand Amino Acids
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•Amino acids found in nature and in proteins are
ʟisomers
▫Exceptions: Some bacteria
▫Monosaccharides prefer ᴅisomers
•Rules for drawing Fischer projection formulas
for amino acid structures
▫—COOH group is placed at the top of the
projection formula

19. Section 20.4
Chiralityand Amino Acids
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▫R group is placed at the
bottom, positions the
carbon chain vertically
▫—NH
2group is placed in a
horizontal position
NH
2on the left -ʟisomer
NH
2on the right -ᴅ
isomer

20. Section 20.4
Chiralityand Amino Acids
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Practice ExerciseH
2NC
COOH
CH2
OH
HNH
2
C
COOH
H
CH
2
SH
CHCH
3
CH
2
CH
3
H
2
NC
COOH
H
*
* *
A B C
•Name the following amino acids with correct
designation for the enantiomer (chiral carbon is
indicated by *).

21. Section 20.4
Chiralityand Amino Acids
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With few exceptions, the amino acids found in
nature and in proteins are _____ isomers.
a.alpha
b.beta
c.ᴅ
d.ʟ

22. Section 20.4
Chiralityand Amino Acids
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•In pure form, amino acids are white crystalline
solids
▫Decompose before they melt
•Not very soluble in water
•-amino acids exist as zwitterions in solution
and in solid state
▫Zwitterions: Molecules with positive charge on
one atom and negative charge on another, but
have no net charge

23. Section 20.4
Chiralityand Amino Acids
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Carboxyl groups give up protons to produce a
negatively charged species
Amino groups accept protons to produce a
positively charged species
•Amino acid forms in solution
▫Zwitterions, positive ion, and negative ion
▫Equilibrium shifts with change in pH

24. Section 20.4
Chiralityand Amino Acids
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25. Section 20.4
Chiralityand Amino Acids
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•pH at which an amino acid exists in its
zwitterion form
▫Carries zero net charge
•Different amino acids have different isoelectric
points
Isoelectric Point (pI)

26. Section 20.4
Chiralityand Amino Acids
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An amino acid with a positive charge on one atom
and a negative charge on another atom with an
overall charge of zero is known as a _____.
a.zeroion
b.zwitterion
c.neutral ion
d.neutron

27. Section 20.4
Chiralityand Amino Acids
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•Standard amino acid that has a side chain that
contains a sulfhydryl group (—SH group)
▫Sulfhydryl group imparts cysteine a unique
chemical property
•Cysteine, in the presence of mild oxidizing
agents, dimerizesto form a cystinemolecule
▫Cystinecontains two cysteine residues linked via
a covalent disulfide bond

28. Section 20.4
Chiralityand Amino Acids
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What functional group in the amino acid cysteine
gives it the ability to react with another cysteine to
form a cystine molecule?
a.Amino group
b.Carboxyl group
c.Sulfhydryl group
d.Hydroxyl group

29. Section 20.4
Chiralityand Amino Acids
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•Under proper conditions, amino acids can bond
together to produce a peptide chain
▫Peptide: Unbranched chain of amino acids
Dipeptide -Compound containing two amino acids
Oligopeptide -Peptide with 10 to 20 amino acid
residues
Polypeptide: Long unbranched chain of amino
acids
▫Reaction is between the amino group of one amino
acid and the carboxyl group of another amino acid
Nature of the Peptide Bond

30. Section 20.4
Chiralityand Amino Acids
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Nature of the Peptide Bond
•Length of the amino acid chain can vary from a
few amino acids to hundreds of amino acids
▫Peptide bonds: Covalent bonds between amino
acids in a peptide
•Every peptide has an N-terminal end and a C-
terminal end

31. Section 20.4
Chiralityand Amino Acids
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Peptide Nomenclature
•C-terminal amino acid residue keeps its full
amino acid name
•All of the other amino acid residues have names
that end in -yl
▫-ylsuffix replaces the -ineor -icacid ending of the
amino acid name, except for tryptophan, for which
-ylis added to the name
•Amino acid naming sequence begins at the N-
terminal amino acid residue
•Example: Ala-leu-gly has the IUPAC name of
alanylleucylglycine

32. Section 20.4
Chiralityand Amino Acids
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Isomeric Peptides
•Peptides that contain the same amino acids but
present in different order are different molecules
(constitutional isomers) with different
properties
▫For example, two different dipeptides can be
formed from one molecule of alanine and glycine
•Number of possible isomeric peptides increases
rapidly as the length of the peptide chain
increases

33. Section 20.4
Chiralityand Amino Acids
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How many isomeric peptides are possible from a
peptide of four different amino acids?
a.8
b.12
c.16
d.24

34. Section 20.4
Chiralityand Amino Acids
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Small Peptide Hormones
•Best-known peptide hormones -Oxytocin and
vasopressin
▫Produced by the pituitary gland
▫Hormones are nonapeptides (nine amino acid
residues)
Have six of the residues held in the form of a loop
by a disulfide bond formed from the interaction of
two cysteine residues

35. Section 20.4
Chiralityand Amino Acids
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Small Peptide Neurotransmitters
•Enkephalinsare pentapeptideneurotransmitters
produced by the brain
▫Bind receptor sites in the brain to reduce pain
•Best-known enkephalins
▫Met-enkephalin: Tyr–Gly–Gly–Phe–Met
▫Leu-enkephalin: Tyr–Gly–Gly–Phe–Leu

36. Section 20.4
Chiralityand Amino Acids
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Small Peptide Antioxidant
•Glutathione (Glu–Cys–Gly) -Tripeptide present
in high levels in most cells
▫Regulates oxidation–reduction reactions
▫Antioxidant that protects cellular contents from
oxidizing agents such as peroxides and superoxides
▫Unusual structural feature -Glu is bonded to Cys
through the side-chain carboxyl group

38. Section 20.4
Chiralityand Amino Acids
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What small peptides are produced in the brain to
reduce pain, and which play a role in the “high”
reported by long-distance runners?
a.Oxytocin
b.Vasopressin
c.Enkephalins
d.Glutathione

39. Proteins

40. PROTEINS
➢high MW organic compounds
➢consists of α-amino acids joined by
peptide bonds
➢“proteios” = most important of all
biological substances. -fundamental
constituent of the cell protoplasm

41. Protein
•General definition -Naturally-occurring,
unbranchedpolymer in which the monomer
units are amino acids
•Specific definition -Peptide in which at least 40
amino acid residues are present
▫The terms polypeptide and protein are used
interchangeably to describe a protein
▫Several proteins have >10,000 amino acid
residues

42. Protein
▫Common proteins contain 400–500 amino acid
residues
▫Small proteins contain 40–100 amino acid residues
•More than one polypeptide chain may be present in
a protein
▫Monomeric: Protein which contains one
polypeptide chain
▫Multimeric: Protein which contains two or more
polypeptide chains

43. Structure of Proteins
I. PRIMARY STRUCTURE OF PROTEINS

44. Peptide bond

45. Determination of a protein’s primary
structure by DNA sequencing

46. Structure of Proteins
II. SECONDARY STRUCTURE OF
PROTEINS

47. Structure of Proteins
II. SECONDARY STRUCTURE OF
PROTEINS

48. Structure of Proteins
II. SECONDARY STRUCTURE OF
PROTEINS

49. Structure of Proteins
II. TERTIARY STRUCTURE OF PROTEINS

50. I. Domains
•fundamenta l functional and three –dimensional
structural units of polypeptide s .
•Polypeptide chains that are greater than 200
amino acids in length generally cons is t of two
or more
•domains. The core of a domain is built from
combinations of superse conda ry s tructura l e
lements (motifs ). Folding of the peptide chain
within a doma in usua lly occurs inde pe ndently
of folding in other domains.

51. II. Interactions stabilizing tertiary
structure
•The unique thre e -dime ns iona l s tructure of e
a ch polype ptide is
•determined by its amino acid sequence.
Interactions between the
•amino a cid s ide cha ins guide the folding of the
polypeptide to form a
•compa ct s tructure . The following four types of
interactions cooperate
•in s tabilizing the te rtia ry s tructure s of globula
r proteins .

52. 1. Disulfide bonds

53. 2. Hydrophobic interactions :

54. 3. Hydrogen bonds
•Amino a cid side chains containing oxygen- or
•nitrogen-bound hydrogen, such as in the alcohol groups
of serine
•and threonine, can form hydrogen bonds with electron-
rich atoms,
•such a s the oxygen of a ca rboxyl group or carbonyl
group of a
•peptide bond (Figure 2.11; see also Figure 1.6, p. 4).
Formation of
•hydrogen bonds between polar groups on the surface of
proteins
•and the aqueous solvent enhances the solubility of the
protein

55. 4. Ionic interactions
•Nega tively cha rged groups , such a s the ca
rboxylate
•group (– COO–) in the s ide cha in of a spa rta te
or glutama
•te , can inte ra ct with pos itive ly cha rged
groups such a s the
•amino group (– NH3
•+) in the s ide cha in of lysine (see Figure 2.11

56. III. Protein folding

57. D. Denaturation of proteins
•Protein denaturation results in the unfolding and disorganization of
•a protein’s secondary and tertiary s tructures without the hydrolysis
•of peptide bonds . Denaturing agents include hea t, organic solvents
,
•s trong acids or base s , detergents , and ions of heavy meta ls such
as
•le ad. Denatura tion ma y, under ideal conditions , be revers ible,
such
•tha t the prote in re folds into its origina l na tive s tructure when the
•denaturing agent is removed. However, mos t proteins , once
denatured,
•rema in permanently disordered. Denatured proteins are often
•ins oluble a nd pre cipita te from s olution.

58. E. Role of chaperones in protein
folding
•Protein denaturation results in the unfolding and disorganization of
•a protein’s secondary and tertiary s tructures without the hydrolysis
•of peptide bonds . Denaturing agents include hea t, organic solvents
,
•s trong acids or base s , detergents , and ions of heavy meta ls such
as
•le ad. Denatura tion ma y, under ideal conditions , be revers ible,
such
•tha t the prote in re folds into its origina l na tive s tructure when the
•denaturing agent is removed. However, mos t proteins , once
denatured,
•rema in permanently disordered. Denatured proteins are often
•ins oluble a nd pre cipita te from s olution.

59. Structure of Proteins
II. QUATERNARY STRUCTURE OF
PROTEINS

60. VI. PROTEIN MISFOLDING
•Protein folding is a complex process that can
sometimes result in improperly
•folded molecules. These mis folded prote ins are
usually tagged
•and degraded within the cell (see p. 444).
However, this quality control
•system is not perfect, and intracellular or
extracellular aggregates of misfolded
•proteins can accumulate, particularly as
individuals age. Deposits
•of misfolded proteins are associated with a
number of diseases

61. A. Amyloid diseases
•B. B. Prion dis eases

63. Proteins are naturally occurring polymers in which
the monomer units are _____.
a.triacylglycerols
b.amino acids
c.carbohydrates
d.nucleosides

64. Functions
➢“Working molecules”
▪Structure & support; provides
materials for building & repair
▪Storage and Transport
▪Enzymes
▪Hormones
▪Contraction

65. Section 20.4
Chiralityand Amino Acids
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Classification of Proteins
simple conjugatedderived
Basis:
➢physical and chemical properties
▪Solubility
▪Reaction towards heat

66. Section 20.9
General Structural Characteristics of Proteins
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Protein Classification Based on Chemical Composition
•Simple protein: Protein in which only amino
acid residues are present
–More than one protein subunit may be present
•Conjugated protein: Protein that has one or
more non-amino-acid entities (prosthetic
groups) present in its structure
–One or more polypeptide chains may be present
–Non-amino-acid components may be organic or
inorganic

67. Section 20.4
Chiralityand Amino Acids
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Classification of Proteins
•SIMPLE PROTEINS -true proteins
➢Enzymatic hydrolysis →α-amino
acids and their derivatives
1.Albumins 5. Histones
2. Globulins 6. Protamines
3. Glutelins 7. Scleroproteins
4. Prolamines

68. Section 20.4
Chiralityand Amino Acids
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Classification of Proteins
•CONJUGATED PROTEINS -protein
molecules combined with non-protein.
a. Nucleoproteins-combination of
histoneand protaminewith
nucleic acid
b. Glycoproteins-proteins with a
carbohydratecomponent

69. Section 20.4
Chiralityand Amino Acids
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Classification of Proteins
c. Phosphoproteins-prosthetic group
(H
3PO
4) joined to the protein molecule
d. Chromoproteins-protein compounds
with pigments
e. Lipoproteins-complex of protein
and lipid

70. Section 20.9
General Structural Characteristics of Proteins
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Protein Classification Based on Chemical Composition
–May be classified further based on the nature of
prosthetic group(s) present
•Lipoprotein contains lipid prosthetic groups
•Glycoprotein contains carbohydrate groups
•Metalloprotein contains a specific metal as its
prosthetic group

71. Section 20.4
Chiralityand Amino Acids
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Classification of Proteins
•DERIVED PROTEINS
A. Primary Protein derivatives -
denatured proteins; slight intra-
molecular rearrangement

72. Section 20.4
Chiralityand Amino Acids
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Classification of Proteins
•Primary Protein derivatives
a. Proteans-result from the
preliminary action of water, dilute acids
or enzymes
Ex. Myosan(from Myosin)
Edestan(from Edestin)

73. Section 20.4
Chiralityand Amino Acids
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Classification of Proteins
•Primary Protein derivatives
b. Metaproteans(Infraproteans)-
products of further hydrolysis
Ex. Acid metaproteans(acid
albuminate)
Alkali metaproteans(alkali
albuminate)

74. Section 20.4
Chiralityand Amino Acids
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Classification of Proteins
•Primary Protein derivatives
c. Coagulated proteins-insoluble
products from the action of heat,
alcohol, UVR or mechanical shaking
Ex. Cooked egg albumin,
cooked meat

75. Section 20.4
Chiralityand Amino Acids
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Classification of Proteins
•Secondary Protein derivatives-
products of more extensive hydrolysis
(heat or alcohol)
-soluble in water and not coagulated
by heat
▪Primary and secondary proteoses
▪Peptones
▪Peptides

76. Section 20.9
General Structural Characteristics of Proteins
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A _____ protein contains only amino acid
residues, and a _____ protein contains one or
more non-amino acids in the structures.
a.simple; conjugated
b.simple; prosthetic
c.conjugated; simple
d.conjugated; prosthetic

77. Section 20.9
General Structural Characteristics of Proteins
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•Types of structures -Primary, secondary,
tertiary, and quaternary
•Primary structure: Order in which amino acids
are linked together in a protein
•Every protein has its own unique amino acid
sequence
–Frederick Sanger sequenced and determined the
primary structure for the first protein (insulin) in 1953

78. Section 20.9
General Structural Characteristics of Proteins
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Figure 20.4-Primary
Structure of a Human
Myoglobin

79. Section 20.9
General Structural Characteristics of Proteins
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•Primary structure of a specific protein is the
same within the organism
–Structures of certain proteins are similar among
different species of animals
•Example: Insulin from pigs, cows, sheep, and humans
are similar but not identical
•Amino acids are linked to each other by peptide
linkages

80. Section 20.9
General Structural Characteristics of Proteins
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Differences in Animal and Human Insulin
•Immunological reactions gradually increase over
time because animal insulin is foreign to the
human body
•Human insulin produced from genetically
engineered bacteria is available

81. Section 20.9
General Structural Characteristics of Proteins
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Important Points Regarding Peptide Bond Geometry
•Peptide linkages are essentially planar
–For two amino acids linked through a peptide bond,
six atoms lie in the same plane
–Planar peptide linkage structure has considerable
rigidity, therefore rotation of groups about the C—N
bond is hindered
•Cis–transisomerism is possible about C—N bond
•Trans isomer is the preferred orientation

82. Section 20.9
General Structural Characteristics of Proteins
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The order in which amino acids are linked in a
protein is known as the _____ structure.
a.primary
b.secondary
c.tertiary
d.quaternary

83. Section 20.9
General Structural Characteristics of Proteins
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•Arrangement in space adopted by the backbone
portion of a protein
•Types -Alpha-helix (helix) and the beta-
pleated sheet (pleated sheet)
•Alpha-helix structure: A single protein chain
adopts a shape that resembles a coiled spring
(helix)
–Coil configuration maintained by hydrogen bonds
–Twist of the helix forms a right-handed, or clockwise,
spiral

84. Section 20.9
General Structural Characteristics of Proteins
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–Hydrogen bonds
between C=O and
N—H entities are
orientated parallel to
the axis of the helix
–All of the amino acid
R groups extend
outward from the
spiral
•There is not enough
room within the
spiral

85. Section 20.9
General Structural Characteristics of Proteins
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•Beta-pleated sheet structure: Two fully
extended protein chain segments in the same or
different molecules
–Held together by hydrogen bonds
•H-bonding between chains -Inter and/or intramolecular

86. Section 20.9
General Structural Characteristics of Proteins
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The two most common types of secondary
structures of proteins are the _____ and the
_____.
a.alpha helix; alpha pleated sheet
b.beta helix; alpha pleated sheet
c.alpha helix; beta pleated sheet
d.beta helix; beta pleated sheet

87. Section 20.9
General Structural Characteristics of Proteins
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•Overall three-dimensional shape of a protein
•Results from the interactions between amino
acid side chains (R groups) that are widely
separated from each other
•Types of stabilizing interactions observed
–Covalent disulfide bonds
–Electrostatic attractions (salt bridges)
–Hydrogen bonds
–Hydrophobic attractions

88. Section 20.9
General Structural Characteristics of Proteins
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Types of Stabilizing Interactions
•Disulfide bonds -Covalent, strong, and involve
two cysteine units
•Electrostatic interactions (salt bridges) -Involve
the interaction between charged side chains of
acidic and basic amino acids
•Hydrogen bonds -Can occur between amino
acids with polar R groups
•Hydrophobic interactions -Occur when two
nonpolar side chains are close to each other

89. Section 20.9
General Structural Characteristics of Proteins
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Figure 20.13 -Stabilizing Influences that Contribute to
the Tertiary Structure

90. Section 20.9
General Structural Characteristics of Proteins
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What type of attractive interaction, that contributes
to the tertiary structure of a protein, would be
found buried in a nonaqueous environment within
the protein?
a.Hydrogen bonds
b.Salt bridges
c.Hydrophilic interactions
d.Hydrophobic interactions

91. Section 20.9
General Structural Characteristics of Proteins
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•Organization among the various peptide
subunits in a multimeric protein
–Highest level of protein organization
–Found in proteins that have two or more polypeptide
chains (subunits)
–Subunits are independent of each other and not
covalently bonded to each other
–Contain even number of subunits

92. Section 20.9
General Structural Characteristics of Proteins
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The structure of hemoglobin, with organization of
its alpha and beta subunits, is an example of what
type of protein structure?
a.Primary
b.Secondary
c.Tertiary
d.Quaternary

93. Section 20.9
General Structural Characteristics of Proteins
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•Reverse of peptide bond formation
–Results in the regeneration of an amine and
carboxylic acid functional groups
–Protein digestion -Enzyme-catalyzed hydrolysis
•Free amino acids produced are absorbed into the
bloodstream and transported to the liver for the
synthesis of new proteins
–Hydrolysis of cellular proteins to amino acids is an
ongoing process, as the body resynthesizes needed
molecules and tissue

94. Section 20.9
General Structural Characteristics of Proteins
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Which of the following best describes what
happens to a small peptide when placed in an acid
solution and heated?
a.The small peptide combines to form a long-chain protein.
b.The small peptide is resistant to acid and heat.
c.The small peptide undergoes hydrolysis to produce free
amino acids.
d.The small peptide undergoes hydrolysis to produce free
amino acids, which recombine upon cooling to form a
different peptide.

95. Section 20.9
General Structural Characteristics of Proteins
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•Partial or complete disorganization of a protein’s
characteristic three-dimensional shape
–Occurs due to disruption of its secondary, tertiary, and
quaternary structural interactions
•Coagulation -Precipitation out of biochemical
solution of denatured protein
–Example: Egg white is a concentrated solution of
protein albumin, which forms a jelly when heated

96. Section 20.9
General Structural Characteristics of Proteins
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•Cooking denatures proteins
–Makes it easy for enzymes in our body to
hydrolyze/digest protein
–Kills microorganisms by denaturation of proteins
•A fever of above 106°F is dangerous
–Denatures and inactivates the body’s enzymes,
which function as catalysts

97. Section 20.9
General Structural Characteristics of Proteins
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What is the consequence of protein denaturation?
a.Partial or complete loss of a protein’s three-dimensional
structure
b.Loss of biochemical activity of the protein
c.Disruption of the secondary, tertiary, and quaternary
structural interactions
d.All the above

98. Section 20.9
General Structural Characteristics of Proteins
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•Fibrous proteins: Protein molecules with
elongated shape
–One dimension is much longer than the others
–Generally insoluble in water
–Have a single type of secondary structure
–Tend to have simple, regular, and linear structures
–Aggregate together to form macromolecular
structures
•Example: Hair, nails, etc

99. Section 20.9
General Structural Characteristics of Proteins
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•Globular proteins: Protein molecules with
peptide chains folded into spherical or globular
shapes
–Water soluble substances -Hydrophobic amino acid
residues are in the protein core
•Membrane proteins: Proteins associated with
cell membranes
–Insoluble in water -Hydrophobic amino acid residues
are on the surface

100. Section 20.9
General Structural Characteristics of Proteins
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Fibrous Proteins: -Keratin
•Provide protective coating for organisms
•Major protein constituent of hair, feather, nails,
horns, and turtle shells
•Mainly made of hydrophobic amino acid
residues
•Individual molecules are almost wholly helical
–Pairs of these helices twine about one another to
produce a coiled coil
–Coiling at higher levels produces the strength
associated with -keratin-containing proteins

101. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
Fibrous Proteins: Collagen
•Most abundant protein in humans (30% of total
body protein)
•Major structural material in tendons, ligaments,
blood vessels, and skin
•Organic component of bones and teeth
•Predominant structure -Triple-helix
–Glycine and proline help maintain the structure of the
triple-helix

102. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
Globular Proteins: Hemoglobin
•An oxygen-carrier molecule in blood
–Transports oxygen from lungs to tissues
•Tetramer (four polypeptide chains)
–Each subunit contains a heme group
•One molecule can transport up to four oxygen
molecules at time
•Iron atom in heme interacts with oxygen

103. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
Globular Proteins: Myoglobin
•Oxygen-storage molecule in muscles
•Monomer
–Consists of a single peptide chain and one heme unit
–One molecule carries one O
2molecule
•Has a higher affinity for oxygen than hemoglobin
•Oxygen stored in myoglobin molecules serves
as a reserve source for working muscles when
oxygen demand exceeds its supply

104. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
Aqueous soluble proteins fold into a spherical or
globular shape. Which of the following contains
only soluble proteins?
a.Fibrin, insulin, hemoglobin
b.Myoglobin, myosin, keratin
c.Hemoglobin, insulin, immunoglobulin
d.Elastin, myosin, keratin

105. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
•Proteins play crucial roles in biochemical
processes
•Diversity of functions exhibited by proteins
exceeds the role of other biochemical molecules
•Functional versatility of proteins stems from their
ability to:
–Bind small molecules specifically and strongly
–Bind other proteins and form fiber-like structures
–Integrate into cell membranes

106. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
•Catalytic proteins are known for their role as
catalysts
–Almost every chemical reaction in the body is driven
by an enzyme
•Defense proteins are central to functioning of the
body’s immune system
–Known as immunoglobulins or antibodies
•Transport proteins bind to small biomolecules,
transport them to other locations in the body,
and release them as needed

107. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
•Messenger proteins transmit signals to
coordinate biochemical processes between
different cells, tissues, and organs
–Examples: Insulin, glucagon, and human growth
hormone
•Contractile proteins are necessary for all forms
of movement
–Examples: Actin and myosin
–Human reproduction depends on the movement of
sperm, which is possible because of contractile
proteins

108. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
•Structural proteins confer stiffness and rigidity
–Collagen is a component of cartilage
–-keratin gives mechanical strength and protective
covering to hair, nails, feathers, and hooves
•Transmembrane proteins control the movement
of small molecules and ions through the cell
membrane
–Have channels to help molecules enter and exit the
cell
–Selective, allow passage of only one type of molecule
or ion

109. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
•Storage proteins bind (and store) small
molecules
–Ferritin -Iron-storage protein which saves iron for use
in the biosynthesis of new hemoglobin molecules
–Myoglobin -Oxygen-storage protein present in
muscle
•Regulatory proteins are found embedded in the
exterior surface of cell membranes
–Act as sites for receptor molecules
–Bind to enzymes (catalytic proteins) and control
enzymatic action

110. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
•Storage proteins bind (and store) small
molecules
–Ferritin -Iron-storage protein which saves iron for use
in the biosynthesis of new hemoglobin molecules
–Myoglobin -Oxygen-storage protein present in
muscle
•Regulatory proteins are found embedded in the
exterior surface of cell membranes
–Act as sites for receptor molecules
–Bind to enzymes (catalytic proteins) and control
enzymatic action

111. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
Which of the following proteins plays the role of
biochemical catalysts in the human body?
a.Hormones
b.Enzymes
c.Transferrin
d.Antibodies

112. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
•Contain carbohydrates or carbohydrate
derivatives in addition to amino acids
–Examples: Proteins in cell membrane and blood
group markers of the ABO system
•Collagen
–Structural feature -4-hydroxyproline (5%) and 5-
hydroxylysine (1%)
–Carbohydrate units are attached by glycosidic
linkages to collagen at its 5-hydroxylysine residues
•Direct the assembly of collagen triple helices into
collagen fibrils

113. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
Immunoglobulins
•Produced as a protective response to the
invasion of microorganisms or foreign molecules
•Serve as antibodies to combat invasion of the
body by antigens
–Antigen: Foreign substance, such as a bacterium or
virus, that invades the human body
–Antibody: Biochemical molecule that counteracts a
specific antigen

114. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
Immunoglobulins
•Bonding of an antigen to variable regions of
immunoglobulins occurs through hydrophobic
interactions, dipole–dipole interactions, and
hydrogen bonds

115. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
An _____ is a glycoprotein produced by an
organism in response to an invasion of a foreign
substance known as a _____.
a.antibody; antigen
b.antigen, immunoglobulin
c.antigen; antibody
d.antibody; immunoglobulin

116. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
•Conjugated proteins that contain lipids and
amino acids
•Help suspend lipids and transport them through
the bloodstream
•Classes of plasma lipoproteins
–Chylomicrons -Transport dietary triacylglycerols from
intestine to the liver and to adipose tissue

117. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
–Very-low-density lipoproteins (VLDL) -Transport
triacylglycerols synthesized in the liver to adipose
tissue
–Low-density lipoproteins (LDL) -Transport
cholesterol synthesized in the liver to cells throughout
the body
–High-density lipoproteins (HDL) -Collect excess
cholesterol from body tissues and transport it back to
the liver for degradation to bile acids

118. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
Which class of plasma lipoproteins is responsible
for transporting cholesterol synthesized in the liver
to cells throughout the body?
a.Chylomicrons
b.Very-low-density lipoproteins (VLDLs)
c.Low-density lipoproteins (LDLs)
d.High-density lipoproteins (HDLs)

119. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
Concept Question 1
The peptide met-gly-phe-ser-ala is known as a _____.
The N-terminal amino acid is _____, and the C-
terminal amino acid is _____. The IUPAC name of this
peptide is _____.
a.pentapeptide; alanine; methionine;
methionineglycinephenylalanineserinealanine
b.hexapeptide; methionine; alanine;
methionineglycinephenylalanineserinealanine
c.hexapeptide; alanine; methionine;
methionylglycylphenylalanylserylalanine
d.pentapeptide; methionine; alanine;
methionylglycylphenylalanylserylalanine

120. Section 20.9
General Structural Characteristics of Proteins
Return to TOC
Concept Question 2
Egg whites are made up of albumin, a single-chain
protein. Why does the albumin solidify when placed in
a hot skillet?
a.Heat causes denaturation of albumin destroying its primary,
secondary, tertiary, and quaternary structures.
b.Heat causes denaturation of albumin destroying its secondary,
tertiary, and quaternary structures.
c.Heat causes denaturation of albumin destroying its secondary
and tertiary structures.
d.Heat causes albumin chains to fuse together through the
formation of new covalent bonds between the chains.

121. Section 20.4
Chiralityand Amino Acids
Return to TOC
PHYSICAL AND CHEMICAL
PROPERTIES OF PROTEINS
•generally tasteless when pure;
amorphous
•insolublein fat solvents; vary in their
solubility in water, salt solution, dilute
acid and alkali
•High MW, non-diffusible colloid
(emulsoidtype)

122. Section 20.4
Chiralityand Amino Acids
Return to TOC
PHYSICAL AND CHEMICAL
PROPERTIES OF PROTEINS
•Amphoteric
•Labile
▫Very reactive & highly specific
due to the presence of side chains
& active NH
2groups

123. Section 20.4
Chiralityand Amino Acids
Return to TOC
SOLUBILITY
Factors Affecting Solubility:
1.Neutral salt
➢“salting in” effect: low concentration
→increases solubility
➢“salting out” effect: increased
conc’n→decreases solubility

124. Section 20.4
Chiralityand Amino Acids
Return to TOC
SOLUBILITY
Factors Affecting Solubility:
2. pH:
➢proteins are amphotericin nature
➢solubility is minimum at isoelectric
point and increases with acidity or
alkalinity

125. Section 20.4
Chiralityand Amino Acids
Return to TOC
SOLUBILITY
Factors Affecting Solubility:
3. Organic solvents: (alcohol, acetone)
➢lowers dielectric constant→
increase electrical forces→
decrease solubility

126. Section 20.4
Chiralityand Amino Acids
Return to TOC
SELECTIVE SEPARATION
➢pH ; Temperature
➢alcohol concentration
➢protein concentration
➢salt concentration kept at low
level.
❖Sedimentation;
Ultracentrifugation
❖Dialysis

127. Section 20.4
Chiralityand Amino Acids
Return to TOC
E.g. Fractionation of plasma :
➢Fibrin film & foam –used for surgery
➢Albumin –treatment of shock,
nephrosis, cirrhosis
➢Globulin –passive immunization
➢Agglutinins –for blood typing

128. Section 20.4
Chiralityand Amino Acids
Return to TOC
ACTION OF HEAT
•Denaturation-proteins undergo
slight intramolecular
rearrangements when they are
heated between 50 –60°C
•Reversible process
•Renaturation, Refolding or
Annealing

129. Section 20.4
Chiralityand Amino Acids
Return to TOC
ACTION OF HEAT
•Coagulation: linkage of adjacent
protein molecules by means of
Hydrogen bonds.
: further heating will cause
matting together →insoluble
(irreversible)

130. Section 20.4
Chiralityand Amino Acids
Return to TOC
ACTION OF HEAT
Other Denaturing Factors:
•Low temperature
•high pressure
•light,; UVR
•surface action
•mechanical agitation
•chemical agents (e.g. acid, alkali,
organic solvents, etc.)

131. Section 20.4
Chiralityand Amino Acids
Return to TOC
PRECIPITATION
1. By Acids-due to presence of the
NH
2 group in their molecules.
CHON (NH
2) + acids ➔insoluble
salts

132. Section 20.4
Chiralityand Amino Acids
Return to TOC
PRECIPITATION
Acids
•Organic acid: TCA, PTA, PMA, Picric,
Tannic acids
➢TA & PA: used for treating burns
•Inorganic acids: HNO
3(Heller’s test)

133. Section 20.4
Chiralityand Amino Acids
Return to TOC
PRECIPITATION
•Salts of Heavy metals (alkali
metals):Hg, Ag, Pb
CHON (-COOH) + alkali metals ➔
insoluble
salt

134. Section 20.4
Chiralityand Amino Acids
Return to TOC
PRECIPITATION
•In metallic poisoning
egg white and milk
insoluble precipitates
lavage

135. Section 20.4
Chiralityand Amino Acids
Return to TOC
PRECIPITATION
•Alcohol-Maximum precipitation
occurs at isoelectricpoint
•accounts for the antiseptic
property of alcohol.
•Bactericidal: 70% alcohol

136. PROTEIN METABOLISM

137. Chapter 26
Chapter Outline
26.1 Protein digestion and absorption
26.2 Amino acid utilization
26.3 Transamination and oxidative deamination
26.4 The urea cycle
26.5 Amino acid carbon skeletons
26.6 Amino acid biosynthesis
26.7 Hemoglobin catabolism
26.8Proteins and the element sulfur
26.9 Interrelationships among metabolic pathways
26.10B vitamins and protein metabolism

138. Protein Digestion and Absorption
Return to TOC
Section 26.1
•Protein digestion starts in the stomach
–Dietary protein present in the stomach stimulates the
release of gastrin
•Gastrin promotes secretion of pepsinogen and HCl
–HClin the stomach has 3 functions
•Antiseptic properties kill most bacteria
•Denaturing action “unwinds” globular properties
•Acidic property leads to activation of pepsinogen
–Pepsin affects the hydrolysis of 10% peptide bonds

139. Protein Digestion and Absorption
Return to TOC
Section 26.1
•Production of secretin is stimulated by the passage of
small amounts of acidic protein content into the small
intestine
•Secretin stimulates bicarbonate (HCO
3
-
) production,
which in turn helps neutralize acidified gastric content
–Promotes secretion of pancreatic digestive enzymes
trypsin, chymotrypsin, and carboxypeptidase in their
inactive forms

140. Protein Digestion and Absorption
Return to TOC
Section 26.1
Protein Digestive Enzymes in the Intestine
•Proteolytic enzymes
–Enzymes that attack peptide bonds
–Pepsin
–Trypsin
–Chymotrypsin
•Zymogens
–Proteolytic enzymes produced in inactive form

141. Protein Digestion and Absorption
Return to TOC
Section 26.1
•Liberated amino acids are transported into the
bloodstream via active transport process
•The passage of polypeptides and small proteins across
the intestinal wall is uncommon in adults
–In infants, the transport of polypeptides allows the passage
of proteins such as antibodies in colostrum milk from a
mother to a nursing infant to build up immunologic
protection in the infant

142. Section 20.4
Chiralityand Amino Acids
Return to TOC
Protein Digestion in Human Body

143. Protein Digestion and Absorption
Return to TOC
Section 26.1
Protein digestion begins in the _____ and is
completed in the _____, resulting in the release of
amino acids.
a.mouth; stomach
b.mouth; small intestine
c.stomach; small intestine
d.small intestine; liver

144. Protein Digestion and Absorption
Return to TOC
Section 26.1
Amino Acid Pool
•Amino acids formed through digestion process enter the
amino acid pool in the body
•Amino acid pool: The total supply of free amino acids
available for use in the human body
•Sources
–Dietary protein
–Protein turnover: The repetitive process in which proteins
are degraded and resynthesized
–Biosynthesis of amino acids in the liver
–Only nonessential amino acids are synthesized

145. Section 20.4
Chiralityand Amino Acids
Return to TOCNH
2
CHCNHCH- -
R
1
O
R
2 -NHCHCNHCH- -
R
3
O
R
4 -NHCHCNHCH
R
5
O
R
6
COOH
aminopeptidase
endopeptidasecarboxypepidaseNH
2
CHCNHCH
O
R"
COOH
R'
Amino acids+
Amino acids
dipeptidase

146. Section 20.4
Chiralityand Amino Acids
Return to TOC
Amino Acid Absorption
➢Rapid absorption (max. concin
blood: 30 –50 mins. after eating)
➢Enter the amino acid pool
➢A.A. Nitrogen level: 4–8 mg/dL

147. Section 26.2
Amino Acid Utilization
Return to TOC
Nitrogen Balance
•The state that results when the amount of nitrogen taken
into the human body as protein equals the amount of
nitrogen excreted from the body in waste materials
•Types of nitrogen imbalance
–Negative nitrogen imbalance -Protein degradation
exceeds protein synthesis
•Amount of nitrogen in urine exceeds consumed amount
•Results in tissue wasting
–Positive nitrogen imbalance -Rate of protein synthesis
(anabolism) is more than protein degradation (catabolism)
•Indicated by the synthesis of large amounts of tissue

148. Section 20.4
Chiralityand Amino Acids
Return to TOC

149. Section 20.4
Chiralityand Amino Acids
Return to TOC
Ammonia
diffuseblood
intestine
bacteria +NH3CH
2
COOHR
some amino acids are degraded
by intestinal bacteria
PUTREFACTION
AA

150. Section 26.2
Amino Acid Utilization
Return to TOC
Uses of Amino Acids in the Human Body
•Protein synthesis
‒Uses approximately 75% of free amino acids
•Synthesis of non-protein nitrogen-containing compounds
‒Synthesis of purines and pyrimidines
‒Synthesis of hemefor hemoglobin
•Synthesis of nonessential amino acids
‒Essential amino acids cannot be synthesized due to the
lack of an appropriate carbon chain
•Production of energy
‒Amino acids are not stored in the body
•Excesses are degraded
•Each amino acid has a unique degradation pathway

151. Section 26.2
Amino Acid Utilization
Return to TOC
Degradation Pathways
•The amino nitrogen atom is removed and excreted from
the body as urea
•The remaining carbon skeleton is converted to pyruvate,
acetyl CoA, or a citric acid cycle intermediate

152. Section 26.2
Amino Acid Utilization
Return to TOC
Amino acids produced during protein digestion
enter the _____ of the body.
a.energy production pool
b.amino acid pool
c.protein synthesis pool
d.nitrogen balance pool

153. Section 20.4
Chiralityand Amino Acids
Return to TOC
Protein Metabolism
➢Amino acid metabolism
➢Fate of Amino Nitrogen (NH
3)
UREA NPN Compounds
Amino acids

154. Section 20.4
Chiralityand Amino Acids
Return to TOC
DYNAMIC ASPECT OF PROTEIN
METABOLISM
❑ZEROor NITROGEN BALANCE :
Equilibrium
N intake = N excretion (adult)

155. Section 20.4
Chiralityand Amino Acids
Return to TOC
Nitrogen balance
❑POSITIVE nitrogen balance:
intake > excretion
➢implies a net gain of protein in the
body
➢pregnancy, infancy, childhood and
recovery from severe illness or
surgery

156. Section 20.4
Chiralityand Amino Acids
Return to TOC
Nitrogen balance
❑NEGATIVE nitrogen balance:
intake < excretion
➢Inadequate intake (fasting, malnutrition
[Kwashiorkor]; diarrhea)
➢Increased catabolism (fever, infection
&wasting disease)
➢increased loss of body proteins
(lactation & albuminuria)

157. Section 20.4
Chiralityand Amino Acids
Return to TOC
UTILIZATION of INORGANIC
NITROGEN (NH
3)
1. Glutamate synthesis
α-ketoglutarate+ NH
3+ NADH +H
+
Glutamate + NAD + H
2O

158. Section 20.4
Chiralityand Amino Acids
Return to TOC
UTILIZATION of INORGANIC
NITROGEN (NH
3)
2. Glutamine synthesis
Glutamate + NH
3+ ATP + H
2O
Glutamine + ADP + Pi + H
2O
Mg
++

159. Section 20.4
Chiralityand Amino Acids
Return to TOC
UTILIZATION of INORGANIC
NITROGEN (NH
3)
3. CarbamylPhosphate synthesis
CO
2+ NH
3+ ATP
CarbamylPO
4+ ADP + H
2O
Mg
++

160. Section 20.4
Chiralityand Amino Acids
Return to TOC
FATE OF NH
3
1.→General NH
3pool of the body
(for metabolic or catabolic
purposes)
2.→Utilized to form glutamine
3.→Urine
4.→Ornithinecycle →Urea

161. Section 20.4
Chiralityand Amino Acids
Return to TOC
Krebs-henseleit cycle
ATP→AMP +
Pi
2ATP→ADP

162. Section 26.4
The Urea Cycle
Return to TOC
Figure 26.6 -Conversion of Carbamoyl Phosphate to
Urea

163. Section 26.4
The Urea Cycle
Return to TOC
•The net effect of transamination and deamination
reactions is the production of ammonium ions and
aspartate
•Ureacycle: A series of biochemical reactions in which
urea is produced from ammonium ions and aspartate as
nitrogen sources
•Urea produced in the liver is transported via blood to the
kidneys and eliminated from the body in urine
•Urea is an odorless white solid with a salty taste, has a
melting point of 133
o
C, and is soluble in water

164. Section 26.4
The Urea Cycle
Return to TOC
Carbamoyl Phosphate
•One of the sources of fuel for the urea cycle
•Two ATP molecules are expended in the formation of
one carbamoyl phosphate molecule
•It contains a high-energy phosphate bond
•It is formed in the mitochondrial matrix

165. Section 26.4
The Urea Cycle
Return to TOC
Steps of the Urea Cycle
•Stage 1 -Carbamoyl group transfer
–The carbamoyl group of carbamoyl phosphate is
transferred to ornithine to form citrulline
•Stage 2 -Citrulline–aspartate condensation
–Citrullineis transported into the cytosol and reacts with
aspartate to produce argininosuccinatesynthetase,
utilizing ATP
•Stage 3 -Argininosuccinatecleavage
–Argininosuccinateis cleaved to arginine and fumarate by
the enzyme argininosuccinatelyase

166. Section 26.4
The Urea Cycle
Return to TOC
Steps of the Urea Cycle
•Stage 4 -Urea from arginine hydrolysis
–Hydrolysis of arginine produces urea and regenerates
ornithine under the influence of arginase
–The oxygen atom present in urea comes from water
–Ornithine is transported back to mitochondria to be used
in the urea cycle

167. Section 26.4
The Urea Cycle
Return to TOC
Urea Cycle Net Reaction
•The equivalent of four ATP molecules is expended in the
production of one urea molecule
–Two molecules of ATP are consumed in the
production of carbamoyl phosphate
–The equivalent of two ATP molecules is consumed in
step two of the urea cycle to give AMP and the PP
i

168. Section 26.4
The Urea Cycle
Return to TOC
Linkage Between the Urea and Citric Acid Cycles
•Fumarate produced is ultimately converted to asparte
•Aspartate re-enters the urea cycle at step two

169. Section 26.4
The Urea Cycle
Return to TOC
The net effect of amino acid degradation is the
production of the ammonium ion, which is toxic.
How is the ammonium ion eliminated from the
body?
a.It is biosynthesized for the production of nonessential
amino acids.
b.It is recycled in the production of amino acids.
c.It is converted to urea in the urea cycle and excreted in
the urine.
d.Both (b) and (c).

170. Section 20.4
Chiralityand Amino Acids
Return to TOC
Schema of Protein Metabolism
BODY PROTEINS DIETARY PROTEINS
FATS
AMINO ACIDS
LABILE PROTEINS
(Liver, Intestines &
Kidneys
ALPHA-KETO
ACIDS
DEAMI-
NATION
Synthesized to hemoglobin,
Tissue proteins, enzymes,
hormones, creatine
NH
3
Reaminated
to Amino
acids
CO
2& H
20 +
Energy
CHO
Purines&
Uric acid
Ammonia Urea

171. Section 26.5
Amino Acid Carbon Skeletons
Return to TOC
•Transamination/oxidative deamination removes the
amino group from an amino acid
–An α-keto acid that contains the skeleton of the amino acid
is produced
•Each of the 20 amino acids undergo a different
degradation process
–Products formed are among a group of seven
intermediates
•Four products are intermediates in the citric acid cycle
•Three products are pyruvate, acetyl CoA, and acetoacetyl
CoA

172. Section 26.5
Amino Acid Carbon Skeletons
Return to TOC
•The amino acids converted to citric acid cycle
intermediates can serve as glucose precursors
–Glucogenicamino acid: An amino acid that has a
carbon-containing degradation product that can be used to
produce glucose via gluconeogenesis
•The amino acids converted to acetyl CoA or acetoacetyl
CoA can contribute to the formation of fatty acids
–Ketogenic amino acid: An amino acid that has a carbon-
containing degradation product that can be used to
produce ketone bodies

173. Section 26.5
Amino Acid Carbon Skeletons
Return to TOC
Figure 26.9 -Fates of Carbon Skeletons of Amino Acids

174. Section 26.3
Transamination and Oxidative Deamination
Return to TOC
•Degradation of an amino acid takes place in two stages
̶Removal of the α-amino group
̶Degradation of the remaining carbon skeleton
•Removal of amino groups requires:
–Transamination: A biochemical reaction characterized by
the interchange of the amino group in an α-amino acid
with the ketogroup in an α-ketoacid
–Oxidative deamination

175. Section 26.3
Transamination and Oxidative Deamination
Return to TOC
Glutamate Production via Transamination
•Glutamate is produced through transamination when α-
ketoglutarate is the amino group acceptor

176. Section 26.3
Transamination and Oxidative Deamination
Return to TOC
Aspartate Production via Transamination
•This occurs when glutamate is the reacting acid and
oxaloacetate is the reacting keto acid

177. Section 26.3
Transamination and Oxidative Deamination
Return to TOC
Ammonium Production via Oxidative Deamination
•Oxidativedeaminationis a biochemical reaction in which
an α-amino acid is converted to an α-keto acid with
release of an ammonium ion
–Occurs in the mitochondria of the liver and kidney

178. Section 20.4
Chiralityand Amino Acids
Return to TOC
DEGRADATION OF AA FOR
ENERGY PRODUCTION
•A. FIVE AMINO ACIDS ARE
DEGRADED TO ACETYL CoA BY WAY
OF PYRUVATE
•Alanine
•Threonine
•Glycine
•Serine
•Cysteine

179. Section 20.4
Chiralityand Amino Acids
Return to TOC
DEGRADATION OF AA FOR
ENERGY PRODUCTION
B. FIVE AMINO ACIDS ARE
DEGRADED TO ACETYL CoA
WITHOUT FORMING PYRUVATE
•Lysine
•Tyrosine
•Phenylalanine
•Tryptophan
•Leucine

180. Section 20.4
Chiralityand Amino Acids
Return to TOC
DEGRADATION OF AA FOR
ENERGY PRODUCTION
C. FIVE AMINO ACIDS FORMING α -
KETOGLUTARATE
•Glutamate
•Glutamine
•Arginine
•Proline
•Histidine

181. Section 20.4
Chiralityand Amino Acids
Return to TOC
DEGRADATION OF AA FOR
ENERGY PRODUCTION
D. AMINO ACIDS FORMING
SUCCINYL-CoA
•Methionine
•Valine
•Isoleucine

182. Section 20.4
Chiralityand Amino Acids
Return to TOC
DEGRADATION OF AA FOR
ENERGY PRODUCTION
E. ASPARTATE & ASPARGINE ARE
DEAMINATED TO OXALOACETATE
•1. Aspartate+ α-ketoglutarate
Oxaloacetate + Glutamate
•2. Aspargine+ H
20 Aspartate
+ NH
4

183. Section 26.3
Transamination and Oxidative Deamination
Return to TOC
Practice Exercise
Indicate whether each of the following reaction characteristics is
associated with the process of transamination or with the
process of oxidative deamination:
a.One of the reactants is a ketoacid and one of the products is a ketoacid.
b.Enzymes with a specificity toward α-ketoglutarateare often active.
c.NAD is used as an oxidizing agent.
d.An aminotransferase enzyme is active.

184. Section 26.3
Transamination and Oxidative Deamination
Return to TOC
What two types of biochemical reactions are
required for the removal of the amino group from
most amino acids?
a.Aminationand reductive deamination
b.Aminationand oxidative deamination
c.Transamination and reductive deamination
d.Transamination and oxidative deamination

185. Section 26.5
Amino Acid Carbon Skeletons
Return to TOC
What are the four intermediates that contain the
carbon skeletons from amino acid degradation in
the citric acid cycle?
a.Citric acid, α-ketoglutarate, acetyl CoA, and fumarate
b.α-Ketoglutarate, succinylCoA, fumarate, and
oxaloacetate
c.α-Ketoglutarate, acetyl CoA, succinylCoA, and
fumarate
d.Citric acid, succinylCoA, fumarate, and oxaloacetate

186. Section 26.6
Amino Acid Biosynthesis
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•Nonessential amino acids are synthesized in fewer steps
than essential amino acids
•The primary source of essential amino acids for humans
and animals is plants

187. Section 26.6
Amino Acid Biosynthesis
Return to TOC
Figure 26.10-Summary of the Starting Materials for the
Biosynthesis of the 11 Nonessential Amino Acids

188. Section 26.6
Amino Acid Biosynthesis
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Which of the following statements is/are true of
amino acids?
a.Nonessential amino acids are synthesized in fewer
steps than essential amino acids.
b.Most bacteria and plants synthesize all amino acids via
pathways that are not present in humans.
c.Plants are the major source of the essential amino acids
in humans and animals.
d.All the above.

189. Section 20.4
Chiralityand Amino Acids
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-End-

190. Section 20.4
Chiralityand Amino Acids
Return to TOC

191. Section 20.4
Chiralityand Amino Acids
Return to TOC
Aliphatic Amino acids
Glycine Alanine
Isoleucine
Valine Leucine
Proline
(Imino acid)

192. Section 20.4
Chiralityand Amino Acids
Return to TOC
Aromatic Amino Acids
Phenylalanine Tyrosine
Tryptophan

193. Section 20.4
Chiralityand Amino Acids
Return to TOC
Sulfur Containing Amino Acids
Methionine Cysteine

194. Section 20.4
Chiralityand Amino Acids
Return to TOC
Acidic Amino Acids
Aspartate Glutamate

195. Section 20.4
Chiralityand Amino Acids
Return to TOC
Hydroxyl-containing side chains
Serine Threonine

196. Section 20.4
Chiralityand Amino Acids
Return to TOC
Amidic Amino acids
Asparagine Glutamine

197. Section 20.4
Chiralityand Amino Acids
Return to TOC
Basic Amino Acids
Lysine Arginine
Histidine

198. Section 20.4
Chiralityand Amino Acids
Return to TOC

199. Section 20.4
Chiralityand Amino Acids
Return to TOC
Acid-Base Properties of amino
Acids
➢

200. Section 26.7
Hemoglobin Catabolism
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Red Blood Cells
•They are highly specialized cells whose primary function
is to deliver oxygen to cells and remove carbon dioxide
from body tissues
•Mature red blood cells have no nucleus or DNA
–Filled with hemoglobin
•Red blood cells are formed in the bone marrow
–Approximately 200 billion new red blood cells are formed
daily
•The life span of a red blood cell is approximately four
months

201. Section 26.7
Hemoglobin Catabolism
Return to TOC
•Hemoglobin is a conjugated protein with two
components
–Globin -The protein portion
–Heme-The prosthetic group
•Iron atom present in hemeinteracts with oxygen
–A reversible complex is formed

202. Section 26.7
Hemoglobin Catabolism
Return to TOC
•Old RBCs are broken down in the spleen and liver
•Degradation of hemoglobin
–Globin protein part is converted to amino acids, which
become part of the amino acid pool
–The iron atom becomes part of ferritin
•An iron-storage protein
–The tetrapyrrolecarbon arrangement of hemeis degraded
to bile pigments
•Eliminated in feces or urine

203. Section 26.7
Hemoglobin Catabolism
Return to TOC
Bile Pigments
•Colored tetrapyrrole degradation products present in bile
•Types of bile pigments
–Biliverdin -Green in color
–Bilirubin -Reddish orange in color
–Stercobilin -Brownish in color
–Urobilin -Yellow in color

204. Section 26.7
Hemoglobin Catabolism
Return to TOC
Bile Pigments
•Daily normal excretion of bile pigments
–1–2 mg in urine
–250–350 mg in feces
•Jaundice
–Caused by an imbalance between the formation and
removal of bilirubin
–Gives the skin and white of the eye the characteristic
yellow tint of the illness

205. Section 26.7
Hemoglobin Catabolism
Return to TOC
Degradation of hemefrom hemolysis produces the
product _____, which is converted to _____.
a.bilirubin; biliverdin
b.biliverdin; bilirubin
c.bilirubin; urobilin
d.stercobilin; urobilin

206. Section 26.7
Hemoglobin Catabolism
Return to TOC
Biodegradation of Cysteine
•Occurs in two steps
–A transamination reaction
–Release of —SH

207. Section 26.7
Hemoglobin Catabolism
Return to TOC
Biosynthesis of Cysteine
•Serine is the precursor
•Serine is converted to cysteine in two steps
–Activation of serine by an acetyl CoA molecule
–Sulfhydration with hydrogen sulphide
•Hydrogen sulphide is produced by sulfate assimilation

208. Section 26.7
Hemoglobin Catabolism
Return to TOC
Figure 26.13 (a) -Steps 1 and 2 of Sulfate Assimilation

209. Section 26.7
Hemoglobin Catabolism
Return to TOC
Figure 26.13 (b) -Steps 3 and 4 of Sulfate Assimilation

210. Section 26.7
Hemoglobin Catabolism
Return to TOC
Figure 26.13 (b) -Steps 3 and 4 of Sulfate Assimilation

211. Section 26.7
Hemoglobin Catabolism
Return to TOC
Hydrogen Sulfide as a Biochemical Signalling Agent
•It regulates vascular blood flow and blood pressure
–Acts as a smooth muscle relaxant and vasodilator
•It influences brain function
–Brain levels of H
2S are lower than normal in cases of
Alzheimer’s disease
•It influences insulin levels in type I diabetes
–Excess of H
2S leads to reduced insulin production

212. Section 26.7
Hemoglobin Catabolism
Return to TOC
In degradation of the sulfur-containing amino acid
cysteine, the sulfuris released in the
form of:
a.hydrogen sulfide.
b.sulfate ion.
c.sulfur dioxide.
d.none of the above.

213. Section 26.7
Hemoglobin Catabolism
Return to TOC
•The metabolic pathways of carbohydrates, lipids, and
proteins are integrally linked to one another
−A change in one pathway can affect many other pathways
•Examples
−Feasting -Over-eating
−Causes the body to store a limited amount as glycogen and
the rest as fat
−Fasting -Food is not ingested
−The body uses its stored glycogen and fat for energy
−Starvation -Prolonged fasting
−Body protein is broken down to amino acids to synthesize
glucose

214. Section 26.7
Hemoglobin Catabolism
Return to TOC
During starvation, what is used as a source of
energy after the glycogen stores have been
depleted?
a.Amino acids of degraded proteins which are used to
synthesize glucose
b.Body fats which are converted to ketone bodies and
used as a source of brain energy
c.Glycogen stores are never depleted
d.Both (a) and (b)

215. Section 26.7
Hemoglobin Catabolism
Return to TOC
•All eight B vitamins participate in various pathways of
protein metabolism
–Niacin
•Oxidative deamination reactions
–PLP
•Transamination reactions

216. Section 26.7
Hemoglobin Catabolism
Return to TOC
Figure 26.15-Involvement of B Vitamins in Protein
Metabolism

217. Section 26.7
Hemoglobin Catabolism
Return to TOC
Transamination reactions require the cofactor PLP,
which involves:
a.folate.
b.riboflavin.
c.vitamin B
6.
d.none of the above.

218. Section 26.7
Hemoglobin Catabolism
Return to TOC
What best describes what happens to the protein
after eating a high-protein meal?
a.Protein digestion begins in the stomach and then moves to the
small intestine where complete digestion occurs. The free amino
acids are stored in the amino acid pool.
b.Proteins are denatured in the stomach and are then moved to the
small intestine for complete digestion.
c.Protein digestion begins in the mouth and then moves to the
stomach for complete digestion by the enzyme pepsin. The free
amino acids are then moved to the small intestine and stored in the
amino acid pool.
d.Protein digestion begins in the mouth, is continued in the stomach,
and is completed in the small intestine.

219. Section 26.7
Hemoglobin Catabolism
Return to TOC
In the early 1990s, nitric oxide (NO) was
discovered in the body as a gaseous chemical
messenger. What effect does nitric oxide have in
the body?
a.It stimulates the urea cycle to ensure proper functioning in the
removal of the toxic ammonium ion.
b.It plays a part in maintaining blood pressure and is found in the
brain where it may play a part in long-term memory.
c.It is rapidly converted to an amino group which is used in amino
acid synthesis.
d.It carries messages into the mitochondria to signal the production
of large amounts of energy when called for by the hormone
epinephrine.