lecture no. 3 biochemistry (clinical biochemistry)

clinical biochemistry

1. Lecture no. 3
Introduction to biochemistry
AMNU 214

2. Protein Structure and Function Review:
Fibrous vs. Globular Proteins

3. •1. Which of the following
factors is not responsible
for the denaturation of
proteins?
•(a) Heat
•(b) Charge
•(c) pH change
•(d) Organic solvents
2. Which of the following
statements is true about
proteins?
•(a) Proteins are made up of
amino acids.
•(b) Proteins are essential for
the development of skin, teeth
and bones.
•(c) Protein is the only nutrient
that can build, repair and
maintain body tissues.
•(d) All of the above
3. How many amino acids make up a
protein?
(a) 10
(b) 20
(c) 30
(d) 50
4. Which of the following statements is true
about the (primary ) 1°structure of
proteins?
(a) The helical structure of the protein
(b) Subunit structure of the protein
(c) Three-dimensional structure of the protein
(d) The sequence of amino acids joined by a
peptide bond

4. –These functions include structural support, storage,
transport of other substances, intercellular signaling,
movement, and defense against foreign substances.
–Enzymes are proteins in a cell that regulate
metabolism by selectively accelerating chemical
reactions.
Proteinsare instrumental
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5. •Proteinsare the most structurally complex molecules known.
–Each type of protein has a complex and unique shape or
conformation.
•All protein polymers are constructed from the same set of 20
monomers, called amino acids.
•Polymers of proteins are called polypeptides.
•A protein consists of one or more polypeptides folded and coiled
into a specific conformation.
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6. •Amino acidsconsist of four components
around a central carbon atom:
–a hydrogen atom
–a carboxyl group
–an amino group
–a variable R group
(or side chain).
Differences in R groups
produce the 20 different
amino acids.
A polypeptide is a polymer of amino acids connected in a specific
sequence
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7. Amino acids –the monomers
There are 20
different amino
acids found in
proteins.
Each has a
different “R”
group (side chain).

8. The twenty amino
acids found in
living organisms,
organized
according to
characteristics of
R-groups. Such
properties
contribute to
proteins folding
into various
shapes

9. Amino acids (monomers) are linked to form
polypeptide chains (polymers) by
dehydration synthesis (condensation reax)
Additional amino acids can be added by condensation reaction.
The covalent bond that forms between amino acids is called a
peptide bond.
Polypeptide chains have an Nterminus and a Cterminus, where
peptide bond forms between amino acids.

10. •A functional proteins consists of one or more
polypeptides that have been precisely twisted,
folded, and coiled into a unique shape.
•It is the order of amino acids that determines
what the three-dimensional conformation will be.
A protein’s function depends on its
specific conformation
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Fig. 5.17

11. •The primary
structureof a
protein is its
unique sequence
of amino acids.
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Fig. 5.18

12. Fig. 5.19
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Even a slight change in primary structure can
affect a protein’s conformation and ability to
function.

13. •The secondary structureof a protein results
from hydrogen bonds at regular intervals along
the polypeptide backbone.
–Typical shapes
–coils (an alpha helix)
–folds (beta pleated sheets)
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Fig. 5.20

14. •The structural properties of silk are due to beta
pleated sheets.
–The presence of so many hydrogen bonds makes
each silk fiber stronger than steel.
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Fig. 5.21

15. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
•Tertiary structureis determined by bonds
among R groups and between R groups and the
polypeptide backbone.
–hydrogen
bonds
–ionic bonds
between charged
R groups
–van der Waals
interactionsamong
hydrophobic R
groups
–disulfide bridges,
strong covalent bonds
Fig. 5.22

16. •Quarternary structureresults from the
aggregation of two or more polypeptide
subunits.
–Collagen is a fibrous protein of three polypeptides
that are supercoiled like a rope.
•This provides the structural strength for their role in
connective tissue.
–Hemoglobin is a
globular protein
with two copies
of two kinds
of polypeptides.
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Fig. 5.23

17. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 5.24

18. Fibrous Proteins
•Include those which
function as structural
proteinsand which play a
role in motility and
contraction
•typically water-insoluble
•built up from single
repeating elements of
secondary structure
•rope-like proteins that
provide strength and
framework to tissues

19. Fibrous Protein Example 1: Collagen
•most abundantprotein in
vertebrates (~ 20 % of all
proteins in human body)
•found in cartilage, tendons,
bones, teeth, skin, and blood
vessels
•extremely strong

20. Fibrous Protein Example 2: α-Keratin
•soft or hard fibrous
protein
•highly insoluble in
water
•composed of
multiple α-helices
twisted into thicker
filaments

21. Globular Proteins
•Include most transport proteins, enzymes, and
hormones
•typicallywater-soluble, roughly spherical and
tightly folded
•hydrophilic nature
–polar residues = on the surface
–hydrophobic residues = on the interior
•many diverse structures are possible

22. Globular Protein Example 1:
Hemoglobin
•each subunit of hemoglobin is
a globular protein with an
embedded heme group. In
adult humans, the most
common hemoglobin protein is
a tetramer consisting of four
polypeptide chains
•The heme group consists of an
iron atom held in a ring, This
iron atom is the site of oxygen
binding.

23. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 5.25
Alterations in pH, salt concentration,
temperature, or other factors can unravel or
denaturea protein.