Functions and Dysfunctions of Protein Processing

Question 1

Sickle Cell Anemia mutation

Answer 1

• 6th codon missense
• Changes Val (hydrophobic) to Glu ( - charged and hydrophilic)
• aggregate and form rigid, rod structure and deform RBC
• poor oxygen capacity and tend to clog capillaries

Question 2

Duchenne Muscular Dystrophy

Answer 2

• IF and OOF deletion in dystrophin gene
• OOF= worst= muscle wasting = death within 10 years
• IF= mild becker syndrome
• • trunacted form of dystrophin
• • treatment: muscle replaced with fat and fibroid

Question 3

Component of mRNA

Answer 3

5’ cap ( 7-methylguanosine)
3” poly A tail
codons

Question 4

component of tRNA

Answer 4

Cloverleaf secondary structure

1) anticodon loop- complimentary codon in mRNA
2) 3’ CCA terminal region
- binds AA that matches corresponding codon

Question 5

enzyme to activate tRNA to aatRNA

Answer 5

aminoacyl tRNA synthetases

1) AAtRNA synthetase catalyzes addition of AMP to COOH to end of AA

Question 6

Translation Inititation

Answer 6

Beginning site on mRNA

• Prokaryotes- Shine Dalgarno sequence (AGGAGG)
• Eukaryotes: 5’cap, 3’ polya tail, kozak sequence, and ATP dependent mRNA scan

initiator tRNA (has GTP) bind to P site of small su (methionylyl tRNA in )

initiation factors added (IFs or eIFs)

large su added

Translation begins with AUG

• one GTP needed

Question 7

Translation Elongation

Answer 7

AAtRNA with gtp

load AAtRNA to A site

peptide bond to met or trna on P site ( peptidyl transferase)

GTP moves aatRNA from A to P site

*2 GTP per AA

Question 8

Translation Termination

Answer 8

Stop codon on A

Release Factors come and bind to A site

Cleave ester bond between C terminus of polypeptide and tRNA

GTP hydrolysis

• 1 GTP per AA

Question 9

Prokaryotic Elongation Inhibitors

Answer 9

Tetracycline- blocks 30s

Chloramphenicol- inhibit peptidyl transferase

Clindamycin/Erthyromycin: block 50s ( translocation)

Streptomycin- block 30s with met-trna

Question 10

Eukaryotic Elongation Inhibitors

Answer 10

Diphtheria toxin- block eEF2 (elongation, translocation)

Cycloheximide- inhibit peptidyl transferase

Shinga/ Ricin- block 60s

Question 11

Elongation inhibitor (both euk and pro)

Answer 11

Puromycin- premature chain termination

-analog to 3’ of aatRNA

Question 12

Protein Sorting Signal Sequence in Cytoplasmic Pathway

Answer 12

Cytoplasm- no signal

Peroxisomes- C terminus SLK signal

Mitochondria- N terminus hydrophobic alpha helix
( need chaperone to protect linear structure - HSP70 for TIM and TOM)

Nucleus- KRKK signal

• begins and ends with free ribosome in cytoplasm

Question 13

Protein Sorting Signal Sequence in Secretory Pathway

Answer 13

ER Lumen- KDEL

Lysosome- Mannose 6 Phosphate

Plasma Membrane- N terminus apolar region

Secretory Protein- tryptophan derivative

• Begins with free ribosomes but ends in ER LUMEN
• > SRP protein brings polypeptide to ER lumen with N terminus + charged/ C terminus hydrophobic alpha helix ( 15-60 AA, 1-2 basic near N terminus, 10-15 hydrophobic on C terminus)
• > SRP halt translation temporarily to bring to ER

Question 14

I- cell disease

Answer 14

defect in TAGGING lysosome proteins with Mannose 6 Phosphate

- increase lysosome enzyme in plasma

Question 15

Chaperones Vs Chaperonins

Answer 15

Chaperone- auxiliary protein that protect protein and help fold them properly into tertiary structure

Chaperonins- have barreled shaped compartments that admit unfolded proteins and catalyze their folding using ATP.

Question 16

Precursor sugar of N-linked glycosylation

Answer 16

phospho dolichol

Question 17

Phosphorylation definition

Answer 17

Formation of ester bond between phosphate and OH
- by Ser/Thr activity adn tyrosine kinase

phosphate removed by phosphatase

Question 18

Di-sulfide bond and location of formation

Answer 18

inter and intra molculular bond

between thiol groups of 2 cysteine

in ER LUMEN

Facilitated by PROTEIN DISULFIDE ISOMERASES

Question 19

PTMS of Collagen

Answer 19

PTM very important

**Ascorbic acid essential for lysyl and prolyl hydroxylases

**Defects in lysyl hydroxylases have skin, bone, joint disorder (Ehlers- Danlos syndrome)