Protein Structure

Question 1

Fibrous proteins

Answer 1

They are insoluble in water
They play a structural role
Examples include alpha keratin and collagen

Question 2

Globular proteins

Answer 2

They are soluble in water
They play functional role
All enzymes are globular proteins

Question 3

Importance of protein

Answer 3

Protein may be broken down to provide energy or provide raw materials for the synthesis of other macromolecules

Question 4

What are the levels of protein structure

Answer 4

Primary structure
Secondary structure
Tertiary structure
Quanternary structure

Question 5

Primary structure

Answer 5

Is the sequence of amino acid in a protein in which a peptide bond connects the alpha carboxyl group of each amino acid to the alpha amino group of the next chain

Question 6

Secondary structure

Answer 6

It refers to the repeating patterns formed by the backbone of at least part of a polypeptide chain which is stabilized by hydrogen bonding

Question 7

Tertiary structure

Answer 7

These are structure with single three dimensional structure and stabilized by bonding between amino acids

Question 8

Quaternanry structure

Answer 8

It is the complete three dimensional structure including the interaction between the component polypeptide chains

Question 9

Bonds involved in the maintenance of protein structure

Answer 9

Hydrogen bond
Disulphide bridges
Van DER Waals bonds
Co ordinate bonds

Question 10

How to determine a primary structure

Answer 10

By the isolation of polypeptide chain i.e to determine the number of different N terminal amino acid and the number of different C terminal amino acids in a polypeptide chain

Question 11

What reagent is used to identify N terminal amino acids

Answer 11

Dansyl chloride
Sanger’s reagent (1-fluoro-2,4-dinitrobenzene)
Edman’s reagent

Question 12

What added advantage does dansyl cloride has when it reacts with alpha amino groups

Answer 12

Dansyl amino acids are highly fluorescent and can be identified in very small quantities by HPLC

Question 13

How is the c terminal amino acid identified

Answer 13

1.It is identified by treating the protein with a reagent that attacks the free carboxyl group e.g sodium borohydride

2.it can also be treated with anhydrous hydrazine at high temperature for several hours in the presence of a catalyst.

Question 14

What happens when the protein is treated with anhydrous hydrazine

Answer 14

Each free carboxyl group react to form a hydrazide

Question 15

What happens when protein is treated with sodium borohydride

Answer 15

The side chain carboxyl group will be reduced with the subsequent production of amino alcohols

Question 16

Ways by which the linkages between various polypeptide chain may be broken

Answer 16

Disulphide bridges maybe broken by treatment with performic acid
Non covalent bond is broken by extremes of pH at high salt concentration or in presence of reagents

Question 17

Determination of the amino acid composition of each polypeptide chain

Answer 17

1. By determining the molecular weight of the polypeptide by the use of size exclusion chromatography then the polypeptide is then completely hydrolysed to it’s component amino acid and the concentration of each determined
2. By ion exchange chromatography in which the eluate is mixed with a reagent such as ninhydrin which reacts with the most amino acid to give blue purple colour.

Question 18

Enzymes used to split long polypeptide chain

Answer 18

Cyanogen bromide which breaks the bond of methionine
Trypsin which breaks the bond on lysine or arginine side chain
Chymotrypsin which breaks the bond on phenylalanine, tryptophan and tyrosine side chain

Question 19

What are the effects of the enzymes on polypeptide chain

Answer 19

It produces a number of peptide fragments which are separated from each other by chromatography or electrophoresis

Question 20

Peptides consisting up to 25 amino acid residues maybe separated directly by means of

Answer 20

Tandem mass spectrometry