Proteins are composed of amino acids linked together in chains. There are 20 common amino acids that make up proteins and each contains different functional groups. A protein's function depends on both its amino acid composition and sequence. Proteins fold into complex 3D shapes like spheres, strands, and sheets. All the information to determine a protein's 3D structure is contained in its linear amino acid sequence. There are essential and non-essential amino acids for human nutrition. Peptides are short chains of amino acids while proteins are longer chains that can assemble into complex structures like alpha helices and beta sheets at the primary, secondary, tertiary, and quaternary levels.

1. Proteins
Submitted by:
sriniketan
REG no. 17BCB0136
SUBMISSION DATE: 11/03/2018

2. INTRODUCTION:-
• Proteins are linear copolymers built from monomeric units called amino acids.
• Amino acids are the building block of protein
• Twenty amino acids are commonly found in proteins.
• These amino acids contain a variety of different functional groups:
Alcohols (R-OH)
Phenols (Ph-OH)
Carboxylic acids (R-COOH)
Thiols (R-SH)
Amines (R-NH2)
• Protein function depends on both
• amino acid content, and
• amino acid sequence.
• Protein fold into diverse shapes such as
• spherical
• elipsoidal
• long strands, etc.

3. • All information for 3-D structure is contained in the linear sequence of amino acids.
• To understand protein function, we must first understand the nature of amino acids.
• Amino acids are essentially α-amino acids:
alpha carbon (IUPAC #2 position)
H2N – C – COOH
|
R
• When R is not H, the alpha carbon is asymetric, giving rise to isomers.

4. – Only L-amino acids are constituents of protiens
Essential Amino Acids:
Need to supplied in daily diet
1. Lysine
2. Leucine
3. Isoleucine
4. Metionine
5. Tryptophan
6. Phenylalanine
7. Threonine
8. Valine

5. Nonessential Amino Acids:
Need not be supplied in daily diet
• Alanine
• Asparagine
• Glycine
• Tyrosine
• Serine
• Proline
• Cysteine
• Cystine
• Histidine(essential for children)
• Glutamine(conditionally essential)
• Arginine(conditionally essential)
• Glutamate

6. – Other few essential amino acids
are

7. Peptide:-
•Copolymer of amino acids:
– a “polypeptide”
Definition:
Amino acid polymers of ≤50 amino acids are called
“polypeptides, peptides, oligopeptides, etc.”
Amino acids polymer of >50 amino acids are called “proteins.”

8. • An example of a “dipeptide” is the sweetener Aspartame.
• Other names include:
– NutraSweet
– Equal
– Tri-Sweet
– Sanecta
IUPAC Name:
“N-L- α – Aspartyl-L-phenylalanine 1-methyl ester”
Abbreviated Structure: Asp – Phe – OCH3
Abbreviated Structure:
• Peptide bonds have partial double bond character due to resonance that limits
rotation about this bond:

9. STRUCTURES OF PROTEINS:--
• Primary (1°) Protein Structure
– linear sequence of amino acids.
• Secondary (2°) Protein Structure
– localized regional structures
• Teritary (3°) Protein Structure
– overal shape of proteins
• Quaternary (4°) Protein Structure
– interactions between proteins

10. Primary (1°) Protein Structure:--
Twisting about various bonds in the polypeptide backbone gives proteins a variety of shapes.
Bond angles give rise to secondary structures. Then, localized secondary structures help drive the peptide folding
that gives rise to tertiary structure.

11. Secondary (2°) Protein Structure:--
• Pauling and Corey proposed two secondary structures in proteins many years before they
were actually proven:
alpha – helix beta - sheet
Both of these secondary protein structures are stabilized by hydrogen bonding between the
carbonyl oxygen atoms and the nitrogen atoms of amino acids in the protein chain.
alpha – helix

12. beta – sheet:--

13. Teritary (3°) Protein Structure
The overall three-dimensional shape of an entire protein molecule is the tertiary
structure.
The protein molecule will bend and twist in such a way as to achieve maximum stability
or lowest energy state. Although the three-dimensional shape of a protein may seem
irregular and random, it is fashioned by many stabilizing forces due to bonding
interactions between the side-chain groups of the amino acids.

14. Quaternary Structure
Many proteins are made up of multiple polypeptide chains, often referred to as protein subunits. These
subunits may be the same (as in a homodimer) or different (as in a heterodimer).
The quaternary structure refers to how these protein subunits interact with each other and arrange
themselves to form a larger aggregate protein complex.
The final shape of the protein complex is once again stabilized by various interactions, including hydrogen-
bonding, disulfide-bridges and salt bridges.

15. • Amino acid sequence of ribonuclease: