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1

AIPMT 2005

MCQ (Single Correct Answer)
Which functional group participates in disulphide bond formation in proteins?
A
Thioester
B
Thioether
C
Thiol
D
Thiolactone

Explanation

Disulphide bond may be reduced to thiol by means of reagents i.e., NaBH4 , which shows the presence of thiol group in disulphide bond formation.
2

AIPMT 2005

MCQ (Single Correct Answer)
The cell membranes are mainly composed of
A
fats
B
proteins
C
phospholipids
D
carbohydrates

Explanation

Cell membranes (Plasma membranes) constitutes bilayer of phospholipid with embedded proteins. In humans, lipids accounts for upto 79% of cell membrance.
3

AIPMT 2004

MCQ (Single Correct Answer)
Which of the following structures represents the peptide chain?
A
B
C
D

Explanation

In peptide linkage i.e., (– CONH) group, the carboxyl group of one amino acid molecule forms an amide by combination with the amino group of the next amino acid molecule with the liberation of water molecule.
4

AIPMT 2004

MCQ (Single Correct Answer)
The helical structure of protein is stablised by
A
dipeptide bonds
B
hydrogen bonds
C
ether bonds
D
peptide bonds

Explanation

The $$\alpha $$-helix structure is formed when the chain of $$\alpha $$-amino acids coils as a right handed screw (called $$\alpha $$-helix) because of the formation of hydrogen bonds between amide groups of the same peptide chain, i.e., NH group in one unit is linked to carbonyl oxygen of the third unit by hydrogen bonding. This hydrogen bonding between different units is responsible for holding helix in a position.

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