MCBG 9 - protein sorting

Question 1

Protein sorting. How do proteins go to ER? SIGNAL AND RECEPTOR
Energy
Where is the protein made?
Specific proteins
Fully folded on entering

Answer 1

KDEL
KDELR -> COPI coat
No
RER
No
YES

Question 2

Protein sorting. How do proteins go to lysosomes? SIGNAL AND RECEPTOR
Energy
Where is the protein made?
Specific proteins
Fully folded on entering

Answer 2

MP6 -Mannose-6-Phosphate
and peptide signal patch
MP6R
ATP proton pump
ER
No
YES

Question 3

Protein sorting. How do proteins go to Nucleus? SIGNAL AND RECEPTOR
Energy
Where is the protein made?
Specific proteins
Fully folded on entering

Answer 3

NLS - Nuclear localisation signal
Binds to Importin (a&B)
Yes - GTP-GDP for Ran
Cytoplasm
Yes RAN
Yes

Question 4

Protein sorting. How do proteins go to Mitochondria? SIGNAL AND RECEPTOR
Energy
Where is the protein made?
Specific proteins
Fully folded on entering

Answer 4

Mitochondrial transport signal
TOMS/TIMs
ATP
cytosplasm
MSF (chapperone proteins prevent it from folding)
No

Question 5

Which codon specifies the first amino acid in any protein?

Answer 5

AUG

Question 6

How might antibiotics work to inhibit translation?

Answer 6

Block binding of tRNA (tetracyclin), prevent peptide bond formation (chloramphenicol) , stop translocation (erythromycin

Question 7

What two processes may be need to occur to a protein after translation?

Answer 7

Proteolytic cleavage and chemical modification

Question 8

Where are proteins destined for the membrane or secretory pathway synthesised?

Answer 8

Ribosomes on RER

Question 9

Where are Protein destined or cytosol, or postranslational import into organelles synthesised?

Answer 9

Free ribosomes (cytosol)

Question 10

What are the four things that are needed for protein sorting?

Answer 10

Signal intrinsic to the protein, receptor to recognise it, translocation machinery, energy

Question 11

What are the two types of exocytosis out of the cell from the golgi

Answer 11

Constitutive

Regulatory

Question 12

What modification occurs in the ER? 3.

Answer 12

Signal cleavage (proteolytic cleavage), 
Disulphide bond formation, 
N-linked Glycosylation
Folding
Assembly of subunits

Question 13

What modification occurs in the Golgi body? 3.

Answer 13

O-linked glycosylation (sugar [glycosyl transferase]-> SER/THR),
Trimming/Modification of N-linked sugar,
Proteolytic processing

Question 14

Why would a protein be made in a non-active form.

Answer 14

Proteins like lysosomes need to be exocytosised

Some may be too large

Question 15

How does a protein know its destined for the peroxisome? Which terminus?

Answer 15

Initial targeting sequence (Peroxisome targeting sequence)

C

Question 16

What is the name of the peroxisome receptor

Answer 16

PTS receptor Pex5

This binds to cargo protein in cytoplasm

Question 17

Protein sorting. How do proteins go to Peroxisome? SIGNAL AND RECEPTOR
Energy
Where is the protein made?
Specific proteins
Fully folded on entering

Answer 17

Peroxisome targeting sequence PTS
Pex5 - binds ot cargo protein in cytoplasm, Binds to Pex5 on outside of peroxisome
Yes - to recycle the PTS receptor

Question 18

Name a peroxisome transport disorder

Answer 18

Zellweger syndrome

Question 19

Give an example of Regulated secretion

Answer 19

Endocrine cells – secreting hormones
Exocrine cells – secreting digestive juices
Neurocrine cells – secreting neurotransmitters

Question 20

What is the enzyme that produces disulphide bonds?

Answer 20

disulphide isomerase

Question 21

What happens if mis-folding can not be corrected? 2

Answer 21

Protein may be returned to cytosol for degradation

Protein may accumulate to toxic levels in the ER resulting in disease

Question 22

What happens if there are folding problems? 1

Answer 22

ER chaperone proteins attempt to correct problem

Question 23

Whats the process of Insulin formation?

Answer 23

RIBOSOME - Pre-proinsulin is translated
ER - Initial sequence cleaved. Di-sulphide bonds, Proteolytic cleavage = Proinsulin
GOLGI - Takes proinsulin and cleaves the pro part. Leaves you with two polypeptide chains parallel with three disulphide bonds