Proteins are the most abundant macromolecules in living systems, and they play a crucial role in many biological processes. Similarly, amino acids are the building blocks of proteins, and their properties and interactions determine the structure and function of proteins. Therefore, understanding the structure and function of proteins and amino acids is essential for understanding many aspects of biochemistry.
Moreover, Amino acids and proteins are fundamental concepts in biochemistry, and they are likely to be tested in the NEET PG exam.
Formed by removal of H2O when two amino acid joined together
During this, carboxy gp of one amino acid and amine group of another amino acid reacts to form amide bond (-CONH-).
If this is present in a protein it is called peptide bond.
It is a strong covalent bond.
It has partial double bond character which is in trans-configuration
Note: In fats, double bond is present but in cis-configuration
Structures of Proteins
Name
Definition
1ᵒ Structure
Sequence of amino acids
2ᵒ structure
Obtained from folding of 1ᵒ structureα Helix (Symmetrical / helical structure)β Sheetsβ Turns
3ᵒ structure
Further folding of 2o structure to form a fully folded 3ᵒ structure
4ᵒ structure
> 1 polypeptide chain e.g. Hb (four polypeptide chains)
Monomeric protein: Those proteins which have only one monomer. They do not have Quaternary structure e.g. myoglobin
Important Information
AA not found in α-helix
Proline and glycine create ‘bend’ in α helix
Tryptophan due to bulky side chain
Aspartate, Glutamate and Valine
Features
1°
2°
3°
4°
Bond
Covalent/ Peptide/ Amide
Hydrogen bond
S~S
Hydrophobic
Hydrogen
Ionic
Hydrophobic
H-bond
Ionic
(Mnemonic- HHI)
Functional activity
Absent
Absent
Present
Present
Denaturation
Retained because peptide bond is very strong
Lost
Lost
Lost
Detection
Mass spectrometry,
Edman’s Technique
X-ray crystallography: Best for crystallizable proteins
NMR spectrometry: Best for non-crystallizable proteins
Important Information
Bonds in Enzyme-Substrate interactions (Mnemonic: HHI)
H - Hydrophobic
H -Hydrogen
I -Ionic
Sometimes covalent but Never Vander Waals Forces
Bonds in Protein-DNA interactions (Mnemonic: HIV)
H -Hydrophobic
I - Ionic
V - Vander Waals Forces
Never Covalent bond
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