Proteins

Question 1

Proteins in native state are

Answer 1

Three dimensional structure

Question 2

Proteins formed of one polypeptide chain have

Answer 2

Primary
Secondary
Tertiary structure

Question 3

Proteins formed of two or more polypeptide chains

Answer 3

Quaternary structure

Question 4

The polypeptide chain starts on the:
Which contains a:
Termed:

Answer 4

Left side
Free terminal amino group group
N-terminus

Question 5

Polypeptide chain ends on:
Contain an amino acid with a:
Termed:

Answer 5

Right side
Free terminal carboxylic group
C-terminus amino acid

Question 6

Primary structure refers to

Answer 6

Amino acid sequence of the polypeptide chain

Question 7

Alpha-helix (4)

Answer 7

Folding of polypeptide chain
Along its long axis
Into specific coiled structure
Held by hydrogen bond

Question 8

Explain maximal stability of a-helix (3)

Answer 8

Intra-chain hydrogen bond
Between NH group and C=O
Each peptide bond participates in the hydrogen bonding

Question 9

R-group of some amino acids disturb the helical structure(3)

Answer 9

Formation of other types of bonds as ionic acids
Ring strict disturb the helical structure
Lysine
Histidine
Proline

Question 10

B-pleated sheet (4)

Answer 10

Polypeptide chain fully extended
Chains line up side by side
To form sheet
2 to 5 adjacent strands

Question 11

B-pleated sheet is stabilized by

Answer 11

Inter-chain hydrogen bond

Question 12

B-pleated between different regions of the same polypeptide chain stabilized by

Answer 12

Intra-chain hydrogen bond

Question 13

Tertiary structure (3)

Answer 13

Folding of polypeptide chain
Into specific higher 3 dimensional structure
Different types of bonds

Question 14

Internal hydrogen bond

Answer 14

Hydroxyl group
Carboxylic group
Ring nitrogen of histidine

Question 15

Quaternary structure

Answer 15

Two or more polypeptide chains

Question 16

Define denaturation (2)

Answer 16

Rupture of chemical bonds that stabilize the secondary, tertiary and quaternary structure of the protein

May be reversible or irreversible

Question 17

Irreversible (3)

Answer 17

May result in protein coagulation
Ex: albumin coagulation by heat
Due to formation of disulfide cross linkage

Question 18

Effects of denaturation on proteins (6)

Answer 18

1. decrease in solubility due to exposure of nonpolar hydrophic bond
2. increased viscosity
3. increase digestibility by proteolytic enzyme due to exposure of peptide bond
4. loss of secondary, tertiary, and quaternary structure
5. loss of biological activity (inactivation of enzymes)
6. loss of antigenic property

Question 19

Fibrous proteins(4)

Answer 19

Polypeptide chains parallel form
Along single axis
To yield long fibers
Ex:collagen/ elastin/keratin

Question 20

Globular proteins (3)

Answer 20

Polypeptide bonds tightly folded

Into compact spherical or globular shapes

Enzymes 
Hemoglobins 
Myoglobin 
Hormones 
Plasma proteins