7. Precursor Processing

Question 0

5’ untranslated region (UTR)

Answer 0

area between the 5’ cap and the first coding exon

Question 1

non-coding mRNA functions as?

Answer 1

regulators of protein translation

Question 2

3’ UTR region

Answer 2

sequence between the last exon and the site of translation termination

Question 3

translocation

Answer 3

proteins made in the cytoplasm, where they can remain or become targeted for movement to other organelles

Question 4

the ribosomes targeted to the ER form proteins that will be?

Answer 4

membrane associated
have transmembrane domains
or are destined for secretion

Question 5

what is the signal hypothesis?

Answer 5

states that certain sequences direct the ribosome to a translocator in the membrane of the ER, which forms a pore for translocation

the protein is processed by signal peptidases to cleave off the signal sequence, and the primary sequence dictates if the protein is a soluble or membrane protein

Question 6

what is translocation directed by?

Answer 6

SRP (signal related peptide)

signal sequence is on the N terminal of the protein

Question 7

when a polypeptide emerges from a ribosome, what does SRP do?

Answer 7

targets the ribosome to the translocator & binds to the SRP receptor & signal sequence

& tightly binds large ribosomal subunit to stop translation

Question 8

hydropathy plot

Answer 8

used to determine the free energy of a reaction where a section of the protein leaves the membrane to enter an aqueous membrane

Question 9

hydrophobic residues

Answer 9

high free energy

unfavorable

Question 10

hydrophilic residues

Answer 10

low free energy/neg free energy

favorable

Question 11

components of a signal peptide/leader sequence

Answer 11

12-36 AAs
significant sequence of basic amino acids
includes initiator methionine & at least 1 positively charged AA
cleavage site for signal peptidases preceded by residues with small R groups

Question 12

when can protein folding occur?

Answer 12

once the polypeptide enters the ER

Question 13

constitutive secretory pathway

Answer 13

unregulated; how many secretory & membrane proteins access the plasma membrane

Question 14

regulated secretory pathway

Answer 14

tightly coupled to signaling cascades to secretory vesicles

Question 15

when proteins leave the ER, where do they go?

Answer 15

to Golgi, then in vesicles to plasma membrane

Question 16

C terminal modification

Answer 16

has amide group to protect against degradation by carboxypeptidases

Question 17

N terminal modification

Answer 17

acetylated, diacetylated, pyrogluatml addition

Question 18

glycine residue in peptides signals what?

Answer 18

amidation

Question 19

3 enzymes that carry out protein precursor processing?

Answer 19

1. proprotein convertase
2. carboxypeptidase
3. peptidyl-glycine a-mono-oxygenase

Question 20

proprotein convertase (PC)

Answer 20

cuts on the C terminal end of basic AAs

Question 21

carboxypeptidase (E)

Answer 21

chews off C terminal amino acids until it reaches glycine

Question 22

peptidyl-glycine a-mono-oxygenase

Answer 22

cuts glycine in half, which leaves amide from the peptide bond

Question 23

example of processing: POMC

Answer 23

processing of the same precursor in different tissues cn make various copies of different, biologically active proteins

Question 24

what happens when the rate of protein synthesis is very fast?

Answer 24

ER can’t keep up in folding proteins, unfolded proteins begin to build up in the ER

Question 25

what is activated when unfolded proteins build up in the ER?

Answer 25

PERK (pancreatic endoplasmic reticulum-resident kinase)

Question 26

what does PERK do?

Answer 26

dimerizes & phosphorylates eIF2, inhibiting protein synthesis & allowing for ER to catch up with protein folding

Question 27

if level of unfolded protein persists?

Answer 27

apoptosis

i. e. family who developed central D.I.
pt. mutation in vasopressin gene did not allow for proper precursor processing, which activated the unfolded protein response & induced apoptosis in the magnocellular neurons