Proteins

Question 1

What are some things that differ between the amino acids?

Answer 1

side chains, size/shape, electric charges, polarity

Question 2

Describe the primary structure of proteins

Answer 2

→ Order of amino acids (‘residues’) in the polypeptide
- Joined with covalent peptide bonds (condensation) between carboxyl groups
- N-terminus and C-terminus (chain has beginning and end)

Question 3

Why must proteins fold into a 3D structure?

Answer 3

To become thermodynamically stable

Question 4

Describe a proteins secondary structure

Answer 4

→ Regular repeating structure between aminos
- Stabilised by hydrogen bonds
- Alpha helix = H-bonds between NH (relatively +) and CO (relatively -) groups of amino acids 4 residues apart
- Beta sheet = H- bonds between NH and CO groups of amino acids further away from each other in the primary sequence - on diff strands

Question 5

Describe a proteins tertiary structure

Answer 5

→ Tightly packed thermodynamically stable 3D structure of the protein
- Determined by noncovalent interactions between the side chains (interactions of differing strengths)
- Some side chains are hydrophilic → can form H-bonds /ionic interactions, tend to fold on outside of tertiary structure
- Others are hydrophobic → nonpolar, no H-bonds/ionic interactions, tend to fold inside of tertiary structure
- Disulfide bridges between Cysteine residues (oxidation/crosslink between sulphur groups)

Question 6

What type of bond is present in the primary structure of protein?

Answer 6

Peptide

Question 7

What type of bond is present in the secondary structure of protein?

Answer 7

H bonds between partially -O2 and partially +NH

Question 8

What type of bond is present in the tertiary structure of protein?

Answer 8

• H bonds
• Ionic
• Disulfide bridges between Cysteine residues

Question 9

Describe the quaternary structure of a protein

Answer 9

• involves subunits (identical/different)
• Dimer, trimer, tetramer = quaternary structures made of 2,3,4 subunits
  E.g Haemoglobin (2 alpha and 2 beta subunits)

Question 10

Describe methylation

Answer 10

addition of -CH3 group(s) e.g methylation of histones controlling genome expression

Question 11

Describe glycosylation

Answer 11

addition of various sugars. Especially present on cell surface and secreted proteins

Question 12

Describe Ubiquitination

Answer 12

addition of a 76-aa polypeptide. Ubiquitin polymers mark protein for degradation

Question 13

Describe phosphorylation

Answer 13

→ reversible addition of phosphate (PO3) groups
- By a class of enzymes kinases
- Important in regulating enzyme function
- Phosphorylation of amino acids in/around active site can change its properties