Question

1. Enzymes catalyze reactions by diverse mechanisms, frequently involving multiple steps. Consider the well-studied enzyme called chymotrypsin, which has three amino acids in its active site: Asp102, His 57, and Ser 195. What is the catalytic role of His 57?

A. covalent catalysis

B. general acid-base

C. catalysis catalysis by approximation

D. metal ion catalysis

2. Which of the following functional groups are not found in carbohydrates?

A. aldehydes

B. hydroxyls

C. ketones

D. thiols

3. What are the components in glycogen?

A. sugars and amino acids

B. sugars and fatty acids

C. sugars and nucleic acids

D. sugars, glycerol and fatty acids

Answer 1

1. Option B is the correct answer.

The catalytic role of His-57 is general acid-base catalysis.

General acid-base catalysis involves those molecules other than water which during an enzymatic reaction acts as a proton acceptor or proton donor. In the catalytic mechanism of chymotrypsin the catalytic role of His-57 is to actually polarize the hydroxyl group so that it can be deprotonated into alkoxide ion which is useful in positioning the seine residue. So, in this enzymatic reaction the proton donor is hydroxyl group and not water so this reaction can be considered to be general acid-base catalysis.

2. Option D is the correct answer.

Thiols are the functional groups which are not found in the carbohydrates. Thiols are generally the sulfur analogue of alcohols. This means that the sulfur group takes the place of oxygen in the alcohol. Thiols are sulfur analogues of alcohols and alcohols come under the fatty acids that is lipids. So, thiols do not come under carbohydrates they come under the lipids.

3. Option D is the correct answer.

The components in glycogen are sugars, glycerol and fatty acids.

So, basically glycogen is made up of glucose molecules which are sugars, major carbohydrates such as sugars, cellulose, starch and glycogen consists of glycerol and fatty acids too along with the sugars. So, option a is the correct answer and other options are incorrect.