Post-translational Modifications

Question 1

List 4 types of post-translational modifications

Answer 1

1. Phosphorylation
2. Glycosylation
3. Protein cleavage
4. Ubiquitination

Question 2

How does phosphorylation modify proteins ?

Answer 2

• reversible
• adds phosphorus on Serine, Threonine, and Tyrosine residues = adds negative charge

Question 3

How does protein cleavage modify proteins ?

Answer 3

• proteases cut proteins to create or remove functions
• irreversible; specifically recognizes polypeptide sequences to prevent unwanted cuts

Question 4

How does glycosylation modify proteins ?

Answer 4

Addition of N-acetyl glycosides to polypeptide in endoplasmic reticulum
- affects how protein folds into tertiary structure

Question 5

How does ubiquitination modify proteins ?

Answer 5

• tags proteins with Ubiquitin (also a protein) = degradation
• E1 (enzyme) binds Ubiquitin = subsequently transfers to E2, and then E3 (holding substrate) = attaches chain of Ubiquitin to substrate
• proteosome unravels ubiquitinated proteins (kind of like a paper shredder barrel)