Protein conformation

Question 1

What are the structural levels of proteins structure ?

Answer 1

1. Primary structure
2. Secondary structure
3. Tertiary structure
4. Quaternary structure

Question 2

What is meant by primary structure of protein ?

Answer 2

It is type , number and sequence of AA in the polypeptide chain and it is genetically determined through the nucleotide sequence of the protein coding region of DNA , it determines secondary , tertiary and quaternary structures.

Question 3

What stabilizes the primary structure of protein ?

Answer 3

It is stabilized by peptide bonds

Question 4

What are the shapes of the secondary structure ?

Answer 4

1. Alpha helix
2. Beta pleated sheets
3. Beta turns

Question 5

What are the characteristics of Alpha helix ?

Answer 5

1. It is a rod ( spiral ) structure .
2. Side chains of amino acids extend outwards from the axis of the helix.
3. A complete turn of the helix contain an average 3.6 aminoacyl residues.
4. Twisting of alpha helix is right handed ( clockwise )

Question 6

What stabilizes the alpha helix ?

Answer 6

Hydrogen bonds

Question 7

What destabilizes the alpha helix ?

Answer 7

1. Two adjacent R groups of the same charge ( Lys and Arg )
2. Two adjacent bulky side chains ( Leucine and Isoleucine )
3. Pro and Gly ( helix breakers )

Question 8

What are the examples of the alpha helix ?

Answer 8

1. Hemoglobin
2. Myoglobin
3. Alpha keratin

Question 9

Describe the structure of the beta pleated sheets .

Answer 9

The polypeptide chains (5-10AA) are arranged in lines side by side forming beta pleated sheets.

Question 10

Why are Beta pleated sheet called pleated ?

Answer 10

Pleated because the radical groups are arranged alternatively slightly above and below the plane of the main chain of polypeptide to form a zigzag like structure.

Question 11

How are the beta pleated sheets stabilized ?

Answer 11

They are stabilized by the hydrogen bonds :

1. Interchain hydrogen bonds : between separate polypeptide chains.
2. Intrachain hydrogen bonds : between segements of the same polypeptide chain.

Question 12

What is the role of Beta turns ?

Answer 12

Enable the polypeptide chain to reverse its direction and fold back on themselves.

Question 13

What are the number of amino acids participating in the beta turns ?

Answer 13

4 amino acids , the first amino acid being hydrogen bonded to the fourth and it contains ( glycine , proline and hydrophilic AAs)

Question 14

What stabilizes Beta turns ?

Answer 14

Hydrogen bonds and ionic bonds

Question 15

What is meant by tertiary structure of proteins ?

Answer 15

Three-dimensional structure of protein. Every protein has a unique tertiary of folded secondary structure (helices , beta pleated sheets and non-regular regions ) in a specific way.

Question 16

Why does every protein have unique tertiary structure ?

Answer 16

As the AAs of the primary structure are brought near the AAs of the secondary structure which results in interactions at different points in the secondary coiled structure forming a 3 dimensional structure that suits the function of the protein.

Question 17

What stabilizes the tertiary structure of proteins ?

Answer 17

1. Covalent bonds : Disulphide bonds

2. Non covalent bonds : Hydrogen , Electrostatic bonds , Hydrophobic interactions.

Question 18

What is the Quaternary structure of proteins ?

Answer 18

It is the arrangement of subunits of proteins consisting of 2 or more polypeptide chains .

Question 19

What are the type of Quaternary structure ?

Answer 19

1. Homogenous proteins : similar subunits

2. Hetrogenous proteins : different subunits

Question 20

What stabilizes Quaternary structure ?

Answer 20

Non covalent interactions

Question 21

What are the examples of Quaternary structures ?

Answer 21

1. Creatine phosphokinase ( dimmer )

2. Hemoglobin : 4 polypeptide chains ( alpha 2 beta 2 )