2. Amino acids - Introduction
Amino acids are organic compounds that contain amine
(–NH2) and carboxyl (–COOH) functional groups, along with
a side chain (R group) specific to each amino acid
Amino acids are the basic structural units of proteins.
All proteins in all species from bacteria to humans are
constructed from the same set of 20 amino acids.
Only L-amino acids are found in proteins except glycine.
3. Amino acid - Definition
“Amino acids are the building blocks of protein, which is
what our bodies use to build and maintain muscles,” says
Fleming.
“Amino acids also help synthesize hormones and
neurotransmitters, which keep our bodies functioning
properly.”
If your body doesn’t get enough of the right amino acids, you
may experience: Decreased immunity, Difficulty thinking
clearly, Digestive issues, Depression, Fertility problems,
4. Amino acids – Structure
Amino acids all share a common basic structure, with a central carbon atom
bound to:
An amine group (NH2)
A carboxylic acid group (COOH)
A hydrogen atom (H)
A variable side chain (R)
5. Amino acids – Classification
Amino acids may be classified according to the chemical
nature of their R groups as:
Aliphatic,
Aromatic,
Heterocyclic, and
Sulphur containing amino acids
6.
7. Amino acids – Classification
1. Amino acids with non-polar aliphatic R groups
This group of amino acids includes:
alanine,
valine,
leucine,
isoleucine and
Proline
glycine.
The hydrocarbon R groups are non-polar and hydrophobic.
8.
9. Amino acids – Classification
2. Amino acids with non-polar aromatic R groups
The amino acids phenylalanine, tyrosine and
tryptophan are included in this group.
All these amino acids are involved in hydrophobic
interactions, which is stronger than aliphatic R
groups.
10. Amino acids – Classification
3. Amino acids with polar, uncharged R groups
Polar uncharged amino acids are:
serine,
threonine,
cysteine,
methionine,
asparagine, and
glutamine.
The R groups of these amino acids are more
hydrophilic than the non-polar amino acids.
11. Amino acids – Classification
4. Amino acids with polar charged R groups
Acidic: The two amino acids with acidic R groups
are aspartic acid and glutamic acid.
Basic: This group includes lysine, arginine and
histidine.
12. Amino acids – Classification
Essential Aminoacids:
Plants and most microorganisms are capable of synthesizing
all the 20 amino acid present in proteins.
But higher animals including man are unable to synthesize
certain amino acids.
The amino acids, which are needed for normal functioning of
the body but cannot be synthesized from metabolic
intermediates, are called essential amino acids.
13.
14. Amino acids – Classification
These amino acids must be obtained from the diet.
Deficiency in any one of the essential amino acids
prevents growth and may even cause death.
The essential amino acids are methionine, arginine,
threonine, tryptophan, valine, isoleucine, leucine,
phenylalanine, and lysine (remember MATTVILPHLy).
15. Amino acids – Properties
Amphoteric properties:
Amino acids are amphoteric compounds as they contain
both acidic (COOH) and basic (NH2) groups.
In acidic solution, amino acids carry positive charges
and hence move towards cathode in an electric field.
In alkaline solution, amino acids carry negative
charges and hence move towards anode in an electric
field.
16. Amino acids – Properties
But, when an amino acid is dissolved in water, it exists
as zwitter ions.
Amino acids possessing both positive and negative
charges are called zwitter ions.
The pH at which the amino acid does not move in an
electric field is called isoelectric pH or isoelectric
point (pI).
At this pH, the amino acid bears a net charge of zero.
19. Amino acids – Properties
ISOMERISM:
All amino acids except glycine possess an asymmetric or
chiral alpha carbon atom.
Hence they exhibit stereoisomerism and optical
isomerism.
Some amino acids are dextrorotatory (+) and some are
leavorotatory (-).
Hence amino acids exist as D(+) and D(-) or L(+) and L(-)
21. Answer the following
1. The amino acid which gives yellow colour with ninhydrin
a) Glycine b) Alanine c) Leucine d) Proline
2. The amino acid with acidic side chain
a) Glycine b) Alanine c) Aspartic acid d) Proline
3. The amino acid with basic side chain
a) Glycine b) Histidine c) Leucine d) Proline
22. Answer the following
4.The amino acid with indole ring
a) Glycine b) phenyl alanine c) tyrosine d) tryptophan
5. An important tripeptide which functions as a
biological reducing agent
a) glutathione b) oxytocin c) vasopressin d) alanylglycine
23. Answer the following
6. ------------------ is non polar aliphatic amino
acids.
a)Glycine b)Phenylalanine c)Tyrosine d) Tryptophan
7.The bond between two amino acids is called -------
-------
A) Amide b)Ester c)Peptide d) Glycosidic
8.Except ------------ all other amino acids are
24. Answer the following
9.Isomerism is due to ----------- carbon atom
a)carboxyl b)free crbon
c)asymmetric d) symmetric
10.------------------- is an example for sulphur amino
acid.
a)Aspartate b) Phenyl alanine
c) Tryptophan d)Methionine
11.------------ is an example for acidic amino acid.
a)Phenyl alanine b) Methionine
25. Answer the following
12.The reagent that is used for quantitative
determination of amino acid is -------------
a)Sanger’s b) Molisch’s c)Benedict’s d) Ninhydrin
13. A hydroxyl amino acid is ----------.
a) Glycine b) Alanine c)Proline d) Serine
26. Answer the following
1. What are Zwitter ions
2. Name some Essential amino acids
3. Write about Amphoteric nature of amino acids.
4. Write about Amino acids with polar, uncharged R
groups
5. Classify Amino acids?
