Protein Structure

Question 1

Protein Structure

Answer 1

1)Primary Structure

2)Secondary Structure

3)Tertiary Structure

4)Quaternary Structure

Question 2

I)Primary structure

Answer 2

1)The primary structure of a protein refers to the amino acid sequence of the polypeptide

2)By convention, the sequence is written with the N-terminus on the left and the C-terminus is on the right

Question 3

II)Secondary Structure

Answer 3

-Primary structure polypeptides can fold to form secondary structures
1)alpha helix

2)Beta pleated sheets (or beta sheets)

3)Beta turns

4)Random coils

-These structures form because of hydrogen bonds. They give proteins strength and flexibility

Question 4

1)Alpha Helix’s structure

Answer 4

The alpha helix is a polypeptide strand folded into a spring-like coil

Question 5

2)Beta-pleated sheet

Answer 5

1)A beta-pleated sheet is a secondary structure consisting of beta strands connected laterally by at least two or three H-bonds, forming a generally twisted pleated sheets

Question 6

Types of Beta-pleated sheets

Answer 6

1)Parallel Beta-pleated sheets

2)Anti-parallel Beta-pleated

Question 7

Parallel Beta-pleated sheets

Answer 7

The adjacent strands are aligned in the same direction

Question 8

Anti-parallel Beta-pleated sheets

Answer 8

The adjacent Beta-strands are aligned in opposite directions

Question 9

III)Beta-turns

Answer 9

1)Hydrogen bonds may occur between peptide bonds that are between 3 to 5 amino acids apart

2)Hairpin turn is a beta-turn where the polypeptide reverse direction and is held by 1 or 2 hydrogen bonds

3)The hydrogen bonds occur in the peptide bonds just like those in beta-sheets

Question 10

IV)Random coils

Answer 10

Random coils are formed by hydrogen bonds of peptide bonds with the functional group on side chains or between side chains

Question 11

3)Tertiary Structure

Answer 11

1)Proteins tend to fold spontaneously into a distinct tertiary structure

2)The tertiary structure is the final 3-D structure of the polypeptide that is folded into a compact stable conformation

3)Folding occurs as a stepwise process. Only the final form is ‘biologically active’

Question 12

The structure for tertiary structure

Answer 12

-A combination of covalent and non-covalent interactions holding the structure together

-May consist of alpha helixes, Beta-sheets, Beta-turns and random coils

Question 13

Tertirary Structure: Protein Folding

Answer 13

1)The structure is stabilised by non-covalent interactions (hydrogen bonds, ionic interactions, hydrophobic interactions, disulfide bonds (only covalent bond))

2)Only the final form is ‘biologically active’

3)In aqueous environments, water-soluble proteins have an internal core that is hydrophobic and external surfaces that are mainly hydrophilic

4)Membrane proteins contain hydrophobic segments that help to embed them into the hydrophobic portions of the phospholipid bilayer

Question 14

4)Quarternary Structure

Answer 14

1)When 2 or more polypeptides (each with its own tertiary structure) combine together they form a quarternary structure

2)Each individual polypeptide in the quarternary structure is known as a subunit

3)The polypeptide subunits are held together by non-covalent interactions and/or disulfide bonds (covalent), similar to the interactions that stabilize the internal structure of a protein

Question 15

Example of a protein with a quarternary structure: Haemoglobin

Answer 15

Haemoglobin: Responsible for carrying oxygen around the body

-Haemoglobin is found in red blood cells

-The hemoglobin is made up of 4 subunits
(2 alpha subunits and 2 beta subunits: Heterotetramer)