Proteins are composed of amino acids linked together by peptide bonds to form polypeptide chains that fold into complex 3D shapes. There are four levels of protein structure - primary, secondary, tertiary, and sometimes quaternary. The primary structure is the specific sequence of amino acids in the chain. Secondary structures include alpha helices and beta pleated sheets formed by hydrogen bonding. Tertiary structure describes the overall 3D shape formed by interactions between R groups of the amino acids. Quaternary structure refers to interactions between multiple polypeptide chains in a single protein.

1. MACROMOLECULE:
PROTEIN
AMINO ACID: STRUCTURE AND
FUNCTION

2. Proteins are biological polymers composed
of amino acids. Amino acids, linked together by
peptide bonds, form a polypeptide chain. One or
more polypeptide chains twisted into a 3-D shape
form a protein. Proteins have complex shapes
that include various folds, loops, and curves.
Folding in proteins happens spontaneously.
Chemical bonding between portions of the
polypeptide chain aid in holding the protein
together and giving it its shape.

3. • There are two general classes of protein
molecules: globular proteins and fibrous
proteins. Globular proteins are generally
compact, soluble, and spherical in shape.
Fibrous proteins are typically elongated and
insoluble. Globular and fibrous proteins may
exhibit one or more of four types of protein
structure. These structure types are called
primary, secondary, tertiary, and quaternary
structure.

4. Protein Structure Levels
The four levels of protein structure are distinguished
from one another by the degree of complexity in the
polypeptide chain. A single protein molecule may
contain one or more of the protein structure types.

5. 1. Primary Structure - describes the unique order in which
amino acids are linked together to form a protein.
Proteins are constructed from a set of 20 amino acids.
Generally, amino acids have the following structural
properties:
• A carbon (the alpha carbon) bonded to the four
groups below:
• A hydrogen atom (H)
• A Carboxyl group (-COOH)
• An Amino group (-NH2)
• A "variable" group or "R" group

7. 2. Secondary Structure - refers to the coiling or folding
of a polypeptide chain that gives the protein its 3-D
shape. There are two types of secondary structures
observed in proteins. One type is the alpha (α)
helix structure. This structure resembles a coiled spring
and is secured by hydrogen bonding in the polypeptide
chain. The second type of secondary structure in proteins
is the beta (β) pleated sheet. This structure appears to
be folded or pleated and is held together by hydrogen
bonding between polypeptide units of the folded chain
that lie adjacent to one another.

9. 3. Tertiary Structure - refers to the comprehensive 3-D
structure of the polypeptide chain of a protein. There are
several types of bonds and forces that hold a protein in its
tertiary structure. Hydrophobic interactions greatly
contribute to the folding and shaping of a protein. The "R"
group of the amino acid is either hydrophobic or
hydrophilic. The amino acids with hydrophilic "R" groups
will seek contact with their aqueous environment, while
amino acids with hydrophobic "R" groups will seek to
avoid water and position themselves towards the center
of the protein.

11. 4. Quaternary Structure - refers to the structure of a
protein macromolecule formed by interactions between
multiple polypeptide chains. Each polypeptide chain is
referred to as a subunit. Proteins with quaternary
structure may consist of more than one of the same type
of protein subunit. They may also be composed of
different subunits. Hemoglobin is an example of a protein
with quaternary structure. Hemoglobin, found in
the blood, is an iron containing protein that binds oxygen
molecules. It contains four subunits: two alpha subunits
and two beta subunits.

13. Amino acids
Amino acids are the building blocks of proteins.
These are necessary ingredients for the growth
of human beings. Amino acids contain both
basic amino groups and acidic carboxyl groups.
The ingredients present in protein are of amino
acids. Both peptides and proteins are the long
chains of amino acids.

14. General properties of Amino Acids
• Amino acids are soluble in water and insoluble in
hydrocarbon solutions.
• They are crystalline solid substances.
• They have very high melting point compared to
their boiling point.

15. List of Amino Acids
• There are around twenty amino acids, which are
involved in the construction of proteins. The lists of
twenty amino acids are:
• Alanine, aspartic acid, asparagines, arginine, cytosine,
cysteine, glycine, glutamine, glutamic acid, histidine,
isoleucine, leucine, lysine, methionine, Proline,
phenylalanine, serine, tyrosine, threonine, tryptophan
and Valine.

16. Essential Amino Acids
There are few amino acids which are essential for
human beings such as: phenylalanine, Valine,
threonine, tryptophan, isoleucine, methionine,
leucine, lysine, and histidine. They are very much
essential, as they cannot be bio synthesized by our
body.

17. Functions of Essential Amino Acids:
• Phenylalanine: Helps in boosting memory power
and also helps to maintain a healthy nervous
system.
• Valine: Helps in growth of muscles.
• Threonine: It promotes the functioning of immune
system.
• Tryptophan: Plays a vital role in maintaining our
appetite.

18. • Isoleucine: Plays a vital role in synthesis of hemoglobin
and it is a major component of RBC (red blood cells).
• Methionine: Helps in maintaining a good and healthy
skin.
• Leucine: It promotes the synthesis of growth hormones.
• Lysine: They are involved in the synthesis of enzymes
and other hormones.
• Histidine: Helps in the production and synthesis of both
RBC (red blood cells) and WBC (white blood cells).

19. Nonessential Amino Acids
There are few amino acids, which are non
essential for human beings as they can be easily
bio synthesized by our body. The non essential
amino acids are: Alanine, cysteine, cystine,
glutamine, glycine, glutamate, arginine, tyrosine,
serine, asparagines, aspartic acid,
selenocysteine and Proline.

20. Functions Non Essential Amino Acids:
• Alanine: Helps in removal of toxic from our body.
• Cysteine: It provides resistance to our body and
inhibits the growth of hairs, nails and etc.
• Cystine: It functions as an antioxidant and protects
our body against radiation and pollutions.
• Glutamine: It is necessary for the synthesis of RNA
and DNA.

21. • Glycine: It acts as a neurotransmitter and plays a vital role in
healing wounds.
• Glutamate: Helps in removal of toxic from our body.
• Arginine: It promotes the biosynthesis of proteins.
• Tyrosine: It plays a vital role in the production of T3 and T4
thyroid hormones.
• Serine: Helps in growth of muscles.
• Asparagines: Helps in the formations of purines and pyrimidines
for the DNA synthesis.
• Aspartic acid: It is similar to asparagines amino acids. It
promotes the synthesis of other amino acids.
• Proline: Helps in regeneration of new skin.

22. Classification of Amino Acids
Amino acids are placed into seven groups based on their
substituent.
• Aliphatic amino acids: Alanine, glycine, isoleucine, leucine, Proline
and Valine.
• Aromatic amino acids: phenylalanine, tryptophan and tyrosine.
• Acidic amino acids: aspartic acid and glutamic acid.
• Basic amino acids: arginine, histidine and lysine.
• Hydroxylic amino acids: serine and threonine.
• Sulphur containing amino acids: cytosine and methionine.
• Amidic amino acids: asparagines and glutamine.

23. Amino acid Abbreviations
Molecular
formula
Linear formula Structural formula
Alanine Ala A C3H7NO2 CH3-CH(NH2)-COOH
Arginine Arg R C6H14N4O2
HN=C(NH2)-NH-(CH2)3-
CH(NH2)-COOH
Asparagine Asn N C4H8N2O3
H2N-CO-CH2-CH(NH2)-
COOH

24. Aspartic
acid
Asp D C4H7NO4
HOOC-CH2-CH(NH2)-
COOH
Cysteine Cys C C3H7NO2S
HS-CH2-CH(NH2)-
COOH
Glutamine Gln Q C5H10N2O3
H2N-CO-(CH2)2-
CH(NH2)-COOH

25. Glutamic acid Glu E C5H9NO4
HOOC-(CH2)2-CH(NH2)-
COOH
Glycine Gly G C2H5NO2 NH2-CH2-COOH
Histidine His H C6H9N3O2
NH-CH=N-CH=C-CH2-
CH(NH2)-COOH

26. Isoleucine Ile I C6H13NO2
CH3-CH2-CH(CH3)-
CH(NH2)-COOH
Leucine Leu L C6H13NO2
(CH3)2-CH-CH2-
CH(NH2)-COOH
Lysine Lys K C6H14N2O2
H2N-(CH2)4-
CH(NH2)-COOH

27. Methionine Met M C5H11NO2S
CH3-S-(CH2)2-
CH(NH2)-COOH
Phenylalanine Phe F C9H11NO2
Ph-CH2-CH(NH2)-
COOH
Proline Pro P C5H9NO2 NH-(CH2)3-CH-COOH

28. Serine Ser S C3H7NO3 HO-CH2-CH(NH2)-COOH
Threonine Thr T C4H9NO3
CH3-CH(OH)-CH(NH2)-
COOH
Tryptophan Trp W C11H12N2O2
Ph-NH-CH=C-CH2-
CH(NH2)-COOH

29. Tyrosine Tyr Y C9H11NO3
HO-Ph-CH2-CH(NH2)-
COOH
Valine Val V C5H11NO2
(CH3)2-CH-CH(NH2)-
COOH

30. Prepared by: Nj Sabile - BSED
Referrences:
http://biology.about.com/od/molecularbiology/ss/proteins.htm
http://biology.tutorvista.com/biomolecules/amino-acids.html