Amino Acids: Structures, Physical and Chemical properties, Groups, Functions

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Amino acids are organic molecules
that, when linked together with other
amino acids, form a protein.
Amino acids are essential to life
because the proteins they form are
involved in virtually all cell functions.
(make up 75% of the body)
Although there are hundreds of amino
acids found in nature, proteins are
constructed from a set of 20 amino
acids.
Amino acids
Introduction

3. Amino acids general structure
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A general representation of a non-ionized amino acid showing
•the carboxylic acid group,
•the α-amino group,
•the hydrogen bonded to the α-carbon, and
•the R group (side chain)
that gives the amino acid its unique properties.

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Obtained
from various
sources & is
considered to
be the building
blocks of life
Involved in
body functions
like growth,
development
healing and
other metabolic
activities
These are
essential for
our daily well-
being as it has
high nutritive
value
Amino acids in our daily life

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Essential
(must be in the diet because
cells can’t synthesize them)
Histidine,
Isoleucine,
Leucin,
Lysine,
Methionine,
Phenylalanine,
Threonine,
Tryptophan,
Valine.
Non-Essential
(can be made by cells)
Alanine,
Arginine,
Asparagine,
Aspartic acid,
Cysteine,
Glutamic acid,
Glutamine,
Glycine,
Proline,
Selenocysteine,
Serine,
Tyrosine.

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Amino acid groups

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Non Polar side chains
Structures
Amino acids with Nonpolar Aliphatic Side Chains
Amino acids with Nonpolar Aromatic Side Chains Other Nonpolar Amino acids

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Polar Side chains

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Electrically charged chains
Acidic

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Electrically charged chains
Basic

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•Amino acids constitute a group of neutral products clearly distinguished
from other natural compounds chemically, mainly because of their
properties and biochemically; mainly because of their role as protein
constituents.

•An amino acid is a carboxylic acid-containing an aliphatic primary amino
group in the α position to the carboxyl group and with a characteristic
stereochemistry.

•Proteins are biosynthesized from 20 amino acids in a system involving
strict genetic control. Thus, amino acids are the basic unit of proteins.
Properties

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Physical Properties

1.Amino acids are colourless, crystalline solid.

2.All have a high melting point greater than 200
o
C

3.Solubility: They are soluble in water, slightly soluble in alcohol and dissolve with
difficulty in methanol, ethanol, and propanol.

R-group of amino acids and pH of the solvent play important role in solubility.

4.On heating to high temperatures, they decompose.

5.All amino acids (except glycine) are optically active.

6.Peptide bond formation: Amino acids can connect with a peptide bond involving
their amino and carboxylate groups. A covalent bond formed between the alpha-
amino group of one amino acid and an alpha-carboxyl group of other forming -
CO-NH-linkage. Peptide bonds are planar and partially ionic.

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A zwitterion is a molecule with functional groups, of which at least
one has a positive and one has a negative electrical charge. Net
charge of the molecule is zero. Amino acids are the best-known
examples of zwitterions.
They contain an amine group (basic) and a carboxylic group (acidic).
The (neutral) zwitterion is the usual form amino acids exist in
solution.
Chemical Properties
Zwitter-ionic property

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As they act as both acids and base since due to the presence two
amine and carboxylic group.
Amphoteric property

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When 1 ml of Ninhydrin solution is added to a 1 ml protein solution
and heated, the formation of a violet color indicates the presence of
α-amino acids.
Ninhydrin test

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The xanthoproteic test is performed for the detection of aromatic amino
acids (tyrosine, tryptophan, and phenylalanine) in a protein solution.
The nitration of benzoid radicals present in the amino acid chain occurs
due to reaction with nitric acid, giving the solution yellow coloration.
Xanthoproteic test

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Reaction with Sanger’s
reagent
(1-fluoro-2, 4-dinitrobenzene)
It reacts with a free amino group in the peptide chain in a mild
alkaline medium under cold conditions.

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Reaction with nitrous acid
Nitrous acid reacts with the amino group to liberate nitrogen
and form the corresponding hydroxyl.

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Glycine, Alanine, Valine, Leucine and Isoleucine have Aliphatic side chains

Amino acids with Nonpolar Aliphatic Side Chains
Non polar side chains
As we move from left to right, the R group becomes more extended and more
hydrophobic.

Example: Isoleucine has a much greater tendency to transfer from water to a
hydrocarbon solvent than Alanline.

Glasses and Vases leave Impression

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Amino acids with Nonpolar Aromatic Side Chains
Phenylalanine, Tyrosine and Trptophan have Aromatic side chains


Phenylalanine together with the aliphatic amino acids Valine, Leucine and
Isoleucine is one of the most hydrophobic amino acids.

Tryptophan and Tyrosine have hydrophobic character as well, but it is tempered by
the polar groups in their side chains.

Tyrosine can ionize at high pH.

Phill trys Ty
(Ty is a brand of plushies)
These compounds are highly conjugated
compounds, absorbs light in the near UV
region of electromagnetic spectrum;
used for the detection and quantification of
proteins by measuring their absorption at
280nm.

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Other Nonpolar Amino acids
Proline and Methionine, These are
secondary α-amino groups that are neither
Aliphatic nor Aromatic.
Proline, in which the side chain forms a covalent bond with the α-amino group.
The proline side chain has a primarily aliphatic character, but like glycine, it is
frequently found on the surfaces of proteins because the rigid ring of its is well
suited in turns.

Methionine, because sulphur has the same electronegativity as carbon, the
thio-ether side chain is quite hydrophobic; thus, methionine displays many of the
same properties as other non polar amino acids.

Prime Minister

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Polar Side chains
Serine, cysteine, threonine, asparagine and glutamine have polar chains, so they
can form multiple H bonds with water molecules and other good H bond donors
and acceptors.

Due to which the five amino acids are most often found on the surfaces of proteins,
where they can contact the aqueous environment in cells or in circulation.

Cystine is formed by the oxidation of two cysteine side chains and it is not coded
for by DNA.

Summers; They Come And Go.

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Electrically
charged chains
Acidic
Aspartic acid and glutamic acid typically carry
negative charges at pH7.

The side chain pKa values of these two
acidic amino acids are so low that the
negatively charged form of the side
chain typically predominates under
physiological conditions, even when
they are incorporated into proteins.
Hence aspartate and glutamate,
respectively
(i.e., as the conjugate bases rather than
as the acids).
AGain

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Electrically charged chains
Basic
Lysine, Arginine and Histidine are
positively charged , basic amino acids.

The pKa value for an ionizable side
chain depends on its electrostatic
environment.

Lysine and Arginine are more basic
than histidine, and their pKa values
indicate that their side chains are
almost always positively charged
under physiological conditions.
.
The basic amino acids are strongly polar, so they are usually found on the exterior
surfaces of proteins, where they can be hydrated by the surrounding aqueous
environment, or in substrate binding clefts of enzymes, where they can interact
with polar groups on the substrate that binds to the enzyme.
Low And High

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1.In particular, 20 very important amino acids are crucial for life as they
contain peptides and proteins and are known to be the building blocks for
all living things.

2.The linear sequence of amino acid residues in a polypeptide chain
determines the three-dimensional configuration of a protein, and the
structure of a protein determines its function.

3.Amino acids are imperative for sustaining the health of the human body.


They largely promote the:
• Production of hormones
• Structure of muscles
• Human nervous system’s healthy functioning
• The health of vital organs
• Normal cellular structure

Functions of Amino acids

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4.The amino acids are used by various tissues to synthesize proteins and to
produce nitrogen-containing compounds

e.g., purines, heme, creatine, epinephrine), or they are oxidized to produce energy.

5.The breakdown of both dietary and tissue proteins yields
nitrogen-containing substrates and carbon skeletons.

6.The nitrogen-containing substrates are used in the biosynthesis of purines,
pyrimidines, neurotransmitters, hormones, porphyrins, and nonessential
amino acids.

7. The carbon skeletons are used as a fuel source in the citric acid cycle, used for
gluconeogenesis, or used in fatty acid synthesis.

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