Protein Structure

Question 1

What is definition of proteins?

Answer 1

Fundamental functional molecules of cell

Question 2

What do proteins provide?

Answer 2

Carrier functions
Metabolic functions 
Form parts of cellular machinery 
Make up structural scaffold 
Sensing molecules

Question 3

Describe the structure of amino acid?

Answer 3

Tetrahedral arrangement of atoms with alpha carbon at its centre
Carboxyl + amine group attached to central carbon
Variable side chain= R group
Hydrogen

Question 4

What happens to amino acid at low pH?

Answer 4

NH2 group accepts H+ to become NH3+

H+ AA acts as base

Question 5

What happens to amino acid at high pH?

Answer 5

The COOH group loses a proton to form COO-

OH- behaves as acid with loss of H+

Question 6

What are 2 isomers of amino acid called?

How are they different?

Answer 6

L amino acid => found in naturally occurring proteins of living organism
D amino acid => found in cell walls of some bacteria

When viewed along axis of hydrogen C-alpha bond, L would read CORN clockwise, D would read CORN in anti-clockwise direction

Question 7

What is a residue?

Answer 7

Each repeating unit of a polypeptide chain

Question 8

Describe the structure of beta sheets ( secondary structure)?

Answer 8

H bonds are formed between beta sheets to stabilise sheet
2 different arrangements where sheet is parallel or antiparallel=> they are formed H bonding between adjacent beta strands connected by loops either in antiparallel or parallel arrangement

Question 9

Describe the structure of alpha helix?

Answer 9

Right handed helix

Stabilised by H bonds between 2 amino acids, 4 residues apart

Question 10

Describe the tertiary structure?

Answer 10

Formed from folding of secondary structure into more densely packed generally globular structure

Question 11

Give an example of proteins that require cofactors?

Answer 11

Haem of haemoglobin
NAD
FAD
Zn2+ , Mg2+ or Other ions

Note that organic cofactors= coenzymes