Question

1. A protein retained on an affinity chromatography column is usually eluted off the column by:

none of these

applying low pressure to the column

gradually increasing the salt concentration of the elution buffer.

adding excess of the protein's ligand.

changing the pH of the elution buffer.

2. In two-dimensional SDS-PAGE protein analysis, proteins in a mixture are separated by their:

affinity for polyacrylamide and overall hydrophobicity

PI and molecular weight

molecular weight and overall hydrophobicity

overall hydrophobicity and PI

affinity for polyacrylamide and molecular weight

3. Which of the following statements is true about active transport?

It is exergonic.

It must be regulated by phosphorylation

It is needed only for the transport of polar molecules.

The transported species can move against its concentration gradient.

4. In membrane proteins, fluidity is decreased by:

higher percentage of shorter chain fatty acids

Increase in cholesterol content

higher percentage of unsaturated fatty acids

decrease in cholesterol content

Answer 1

1. d. adding excess of the proteins ligand.

A particualr  protein will specifically binds with its ligand. Then the protein can be eluted by adding a solution containing the protein's free ligand. Affinity chromatography is used for separating similar type of molecule. So by adding a specific ligand for a specific protein we can separate them.

2. b. PI and molecular weight.

Two dimensional SDS-PAGE  is used to analyze mixtures of proteins by two properties. Proteins are first separated by their PI in isoelectric focusing and then further separated by molecular weight.

3.b and d. It must be regulated by phosphorylation and The transported species can move against its concentration gradient.

In active transport the substances move against the concentration gradient. They move from an area of low concentration to an area of high concentration. So ATP is required hence it is endergonic reaction. As the substance enters the membrane protein he ATP binds and the phosphorylation of protein takes place. This causes addition of phosphate group to the protein and the molecule is released on the other side of the membrane.

4.d. decrease in cholesterol content

Cholestrol acts as a regulator of membrane fluidity. At hugh temperature it stabilises the membrane and at low temperature it goes between the phospholipids and prevent it from clustering. So, if the content of cholestrol is decreased the fluidityof the plasma mambrane will be affected.