Protein folding Flashcards
1
Q
Phosphorylation as a post translational modification
A
- Usually occurs on Ser, Thr, Tyr and sometimes His/Asp
- drugs at on it for cancer
- adds negative charge which can form bonds with other positive structures
- can block access to active sites
2
Q
what are the two types of PTMs
A
Covalent addition to side chains
- phosphorylation
- methylation
- alkylation
- acylation
- glycosylation
- oxidation
Cleavage of protein backbone a specific site
3
Q
Acetylation
A
- acts on lysine on histones and p53
N-terminal acetylation
- acts during protein synthesis and is irreversible
- protect against degradation by blocking n terminus but can also do the opposite
- involved in protein protein interactions
- targeting proteins to membranes, prevents translocation through ER
4
Q
methylation
A
Usually on Lys/ Arg on histone proteins to control expression - uses SAM enzyme
5
Q
S-prenylation
A
C15 or C20 prenyl groups added to Cys and is very hydrophobic
6
Q
Glycosylation
A
- glycosylation adding sugar to protein
- GlcNac is commonly added
O-glycosylation
- adding glycans to protein oxygens
- usually Ser, Thr and Tyr
N-Glycosylation
- more common
- takes place in ER
- Sugars attached in Ser/Thr-X-Asn motif
- used for targeting to golgi and ER
- help chaerones in folding (GroEL recognises sugars)
- Can be found on cell surface
7
Q
Disulphide Bonds
A
- Stabilises proteins and is a redox reation and the further down the secretory pathway the more likely they form
- form by the addition of oxygen
- Bonds broken by use of NADPH and Glutathione reductase
- PDI is an enzyme in the ER which randomly bonds Cys residues but the correct ones are strongest and so stay formed. - chaperone enzyme
8
Q
Transamidations
A
- Method to crosslink side chains by joining Gln and Lys
9
Q
Hydroxylation
A
hydroxylated amino acids all use Fe monooxygenase enzyme to O.
5-OH-Lys usually then glycosylated
10
Q
Collagen
A
- Main protein in bones, skin cartilage and tendons and is most abundant
- tripple helix structure
- sequence of repeats of Gly - Pro and Y, y is usually 4-hydroxyproline
- conversion of Pro to 4-hydroxyproline stabilises structure and Vitamin C is required
- can cause scurvy
11
Q
3-hydroxyasparagine
A
- Asn is hydroxylated into transcription factor HIF initiated with O2 at low pressure
- Induces transcription of hundreds of genes including those that cause EPO to make more red blood cells (used by cheating athletes)
12
Q
Protein modification by bacterial toxin Diphtheria
A
- NAD is split to release nicotinamide and very reactive ribaoxacarbenium ion
- eEF2 elongation factor is involved in transcription and has its His residue modified to diphthamide and then ADP ribosylated by diphtheria toxin and protein synthesis stops
13
Q
Carboxylation of glutamate for calcium binding
A
- Carboxylated Glu binds 2+ metals strongly (Ca)
- common in enzymes invovled in blood clotting and requires vitamin K
- so vitamin K deficiency causes bleeding
14
Q
Ubiquitin and protein turnover cellular protein degradation
A
- proteins within cell constantly turn over
- some proteins are very unstable
- Damaged, mistranslated or oxidised proteins and degraded
- proteins are continuously made, degraded and remade
15
Q
Ubiquitin (Ub)
A
- used in degradation
- used as a tag to tell which protein to be destroyed
- well conserved
