7. Precursor Processing Flashcards

0
Q

5’ untranslated region (UTR)

A

area between the 5’ cap and the first coding exon

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1
Q

non-coding mRNA functions as?

A

regulators of protein translation

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2
Q

3’ UTR region

A

sequence between the last exon and the site of translation termination

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3
Q

translocation

A

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

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4
Q

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

A

membrane associated
have transmembrane domains
or are destined for secretion

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5
Q

what is the signal hypothesis?

A

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

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6
Q

what is translocation directed by?

A

SRP (signal related peptide)

signal sequence is on the N terminal of the protein

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7
Q

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

A

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

& tightly binds large ribosomal subunit to stop translation

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8
Q

hydropathy plot

A

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

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9
Q

hydrophobic residues

A

high free energy

unfavorable

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10
Q

hydrophilic residues

A

low free energy/neg free energy

favorable

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11
Q

components of a signal peptide/leader sequence

A

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

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12
Q

when can protein folding occur?

A

once the polypeptide enters the ER

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13
Q

constitutive secretory pathway

A

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

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14
Q

regulated secretory pathway

A

tightly coupled to signaling cascades to secretory vesicles

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15
Q

when proteins leave the ER, where do they go?

A

to Golgi, then in vesicles to plasma membrane

16
Q

C terminal modification

A

has amide group to protect against degradation by carboxypeptidases

17
Q

N terminal modification

A

acetylated, diacetylated, pyrogluatml addition

18
Q

glycine residue in peptides signals what?

19
Q

3 enzymes that carry out protein precursor processing?

A
  1. proprotein convertase
  2. carboxypeptidase
  3. peptidyl-glycine a-mono-oxygenase
20
Q

proprotein convertase (PC)

A

cuts on the C terminal end of basic AAs

21
Q

carboxypeptidase (E)

A

chews off C terminal amino acids until it reaches glycine

22
Q

peptidyl-glycine a-mono-oxygenase

A

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

23
Q

example of processing: POMC

A

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

24
what happens when the rate of protein synthesis is very fast?
ER can't keep up in folding proteins, unfolded proteins begin to build up in the ER
25
what is activated when unfolded proteins build up in the ER?
PERK (pancreatic endoplasmic reticulum-resident kinase)
26
what does PERK do?
dimerizes & phosphorylates eIF2, inhibiting protein synthesis & allowing for ER to catch up with protein folding
27
if level of unfolded protein persists?
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