1

### AIPMT 2004

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.
2

### AIPMT 2004

The hormone that helps in the conversion of glucose to glycogen is
A
cortisone
B
bile acids
C
D
insulin

## Explanation

Insulin is a hormone secreted by the pancreas that lowers blood glucose level by promoting the uptake of glucose by cells and the conversion of glucose to glycogen by the liver and skeletal muscle.
3

### AIPMT 2004

The correct statement in respect of protein haemoglobin is that it
A
functions as a catalyst for biological reactions
B
maintains blood sugar level
C
acts as an oxygen carrier in the blood
D
forms antibodies and offers resistance to diseases.

## Explanation

Haemoglobin acts as an oxygen carrier in the blood since it reacts with oxygen to form unstable oxyhaemoglobin which easily breaks to give back haemoglobin and oxygen.
4

### AIPMT 2004

Number of chiral carbons in $\beta$-$D$-(+) glucose is
A
five
B
six
C
three
D
four