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MCP Unit 2 > Lectures 19 & 19: Protein Synthesis > Flashcards

Lectures 19 & 19: Protein Synthesis Flashcards

1
Q

How many possible start codons are there?

A

1

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2
Q

How many possible stop codons are there?

A

3

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3
Q

What is the polarity of tln?

A

5’ –> 3’

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4
Q

What is a silent mutation?

A

Does not affect AA produced

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5
Q

What are the components of tRNA? What do they do?

A

3’ end - binds AA which will be added
anticodon loop - associates with mRNA
then also D loop, T loop, 5’ end

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6
Q

What is the wobble hypothesis?

A

first two bases of codon-anticodon interaction are constrained by normal Watson-Crick base-pairing
Requirements for H-bonding at third base are less stringent

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7
Q

What enzyme catalyzes the transfer of a specific AA to the 3’-OH of specific tRNAs (charges tRNA)?

A

aminoacyl-tRNA synthetases

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8
Q

What is the overall aminoacyl-tRNA synthetase rxn?

A

ATP + AA + tRNA –> aminoacyl tRNA* –> AMP + PPi

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9
Q

What are the two steps of the rxn which charges tRNA?

A
  1. activation of AA by rxn w/ ATP to form aminoacyl adenylate
  2. rxn of activated AA with 3’-OH of tRNA to form aminoacyl-tRNA
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10
Q

How is uncharged vs charged tRNA with Ser written?

A 
uncharged = tRNAser
cahrged = ser-tRNAser
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11
Q

What are the subunits of bacterial ribosomes?

A

50S + 30S

70S

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12
Q

What are the subunits of eukaryotic ribosomes?

A

60S + 40S

80S

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13
Q

How many tRNA molecules can one ribosome bind?

A

three

e, p, a

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14
Q

what are the three tRNA binding sites on ribosome called?

A 
E = exit
P = peptidyl
A = aminoacyl
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15
Q

What happens at the A (aminoacyl) tRNA binding site of a ribosome?

A

attachment of incoming aminoacyl-tRNA

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16
Q

What happens at the P (Peptidyl) tRNA binding site of a ribosome?

A

attachment of pepidyl tRNA

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17
Q

What happens at the E (exit) tRNA binding site of a ribosome?

A

harbors spent tRNA

releases it

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18
Q

What happens during tln initiation?

A
  • mRNA binds, aligned in correct reading frame
  • initiator aminoacyl tRNA binds
  • ribosome assembles from small and large subunits
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19
Q

What happens during tln elongation?

A
  • aminoacyl tRNA binds, checks codon-anticodon match
  • new peptide bond is formed
  • growing chain is translocated from A site to P site
  • mRNA is pulled along - next codon exposed to A site
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20
Q

What happens during tln termination?

A
  • release factors bind GTP - bind stop codon in A site
  • peptidyl tRNA in P site is hydrolyzed - release peptide chain, leave tRNA in P site
  • GTP hydrolysis –> release tRNA, release factors, mRNA; ribosome dissociates
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21
Q

How does ribosome know which Met codon is the start codon in prokaryotes?

A

Shine-Dalgarno sequence upstream

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22
Q

How does ribosome know which Met codon is the start codon in eukaryotes?

A

5’ cap (7-methyl guanosine residue)

23
Q

Is mRNA linear or circular during translation in euk and prok?

A

prok - linear

euk - circular (poly-A tail interacts with 5’ cap)

24
Q

which kingdom has polycistronic vs monocystronic tln?

A 
prok = poly
euk = mono
25
Q

What does Polycistronic mean?

A

once ribosome attaches to Shine-Dalgarno sequence, multiple proteins can be made from same mRNA strand

26
Q

What does monocistronic mean?

A

single protein is translated from single mRNA

27
Q

what are initiation factors?

A

proteins which help assemble and disassemble transient complexes during tln
-not permanent parts of ribosome

28
Q

What are the prok initiation factors?

A

IF1, IF2, IF3

29
Q

How many initiation factors do euk have? Which is similar to one of the prok IFs?

A

> 10

eIF-2 ~ IF2

30
Q

What is the role of GTP in tln?

A

catalyze

conf change in ribosomes to accelerate rxns

31
Q

What is the role of GTP hydrolysis in tln?

A

Makes rxns irreversible

32
Q

What do the prok elongation factors do?

A

EF-Tu brings each aatRNA in, checks match

EF-G helps shift mRNA and tRNA

33
Q

How many release factors do prok have?

Euk?

A

prok - 3 (RF 1,2,3)

euk - 1 (eRF)

34
Q

How many elongation factors do prok have? Euk?

A

prok - 3 (EF 1,2,3)

euk - 2 (eEf 1,2)

35
Q

Why doesn’t peptide elongation require nrg?

A

aa-tRNA is charged

36
Q

What do the two active sites of amino acyl sythetases do?

A

one recognizes correct tRNA and attaches AA

Other proofreads - recognizes and removes incorrectly attached AA

37
Q

Which steps of tln require energy?

A 
synthesis of aa-tRNA
initiation
elongation
release polypeptide
proofreading
38
Q

what does phosphorylation of eIF-2 do?

A

decreases rate of protein synthesis

39
Q

What does eIF-2 do?

A

Carries GTP and initiator tRNA to ribosome

40
Q

How does the regulation of globin synthesis in response to heme availability exemplify tln regulation?

A
  • heme is absent –> eIF2 is phosphorylated by HCI = inactive
  • heme is present –> phosphate is removed, tln occurs
41
Q

How is the 5’-cap involved in regulating euk tln?

A
  • protects from nucleases
  • distinguishes btw mRNA and types of tRNA
  • eIFs recognize cap
42
Q

How is the 5’-UTR involved in regulating euk tln?

A

sequences for translational efficiency

43
Q

How is the 3’-UTR involved in regulating euk tln?

A

signal sequences so mRNA is translated in specific places in cell

44
Q

How is the poly-A tail involved in regulating euk tln?

A
  • stabilizes - important for lifespan of mRNA

- may catalyze formation of large ribosomal subunit

45
Q

What feature of mRNA plays a huge role in tln regulation?

A

lifetime

46
Q

what is a key regulatory molecule in tln of the ferritin/transferrin receptor?

A

aconitase

47
Q

In what two ways does aconitase affect tln of the ferritin/transferrin receptor?

A

binds IRE 5’-UTR of ferritin mRNA –> blocks tln initiation

binds IRE 3’-UTR of ferritin mRNA –> stabilizes mRNA against degradation

48
Q

what is the function of ferritin? What happens to the tln of ferritin if [iron] increases?

A

intracellular iron storage protein

increase [iron] increase tln of ferritin

49
Q

what is the function of the transferrin receptor? What happens to the tln of transferrin receptor if [iron] increases?

A

imports iron

increase [iron] decrease tln of transferrin receptor

50
Q

What is endogenous regulation of proteins synthesis?

A

siRNA pr miRNA can down-regulate tln by inducing mRNA degradation

51
Q

What is exogenous regulation of protein synthesis?

A

dsRNA gets processed to siRNA –> degradation of mRNA

52
Q

In what two ways can interferons work?

A 
-inhibition of translation (makes protein kinase - phosphorylation of eEf-2)
mRNA degradation (produces endoribonuclease --> mRNA non-functional)
53
Q

How is an interferon produced?

A
  • virus produces dsRNA = signal to host that there is a viral infection
  • host cells secrete interferons (IFNs)
  • IFNs bind to other cells, induce expression of enzymes which will interfere with protein synthesis

MCP Unit 2 (17 decks)

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