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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
What does Polycistronic mean?
once ribosome attaches to Shine-Dalgarno sequence, multiple proteins can be made from same mRNA strand
26
What does monocistronic mean?
single protein is translated from single mRNA
27
what are initiation factors?
proteins which help assemble and disassemble transient complexes during tln -not permanent parts of ribosome
28
What are the prok initiation factors?
IF1, IF2, IF3
29
How many initiation factors do euk have? Which is similar to one of the prok IFs?
>10 | eIF-2 ~ IF2
30
What is the role of GTP in tln?
catalyze | conf change in ribosomes to accelerate rxns
31
What is the role of GTP hydrolysis in tln?
Makes rxns irreversible
32
What do the prok elongation factors do?
EF-Tu brings each aatRNA in, checks match | EF-G helps shift mRNA and tRNA
33
How many release factors do prok have? | Euk?
prok - 3 (RF 1,2,3) | euk - 1 (eRF)
34
How many elongation factors do prok have? Euk?
prok - 3 (EF 1,2,3) | euk - 2 (eEf 1,2)
35
Why doesn't peptide elongation require nrg?
aa-tRNA is charged
36
What do the two active sites of amino acyl sythetases do?
one recognizes correct tRNA and attaches AA | Other proofreads - recognizes and removes incorrectly attached AA
37
Which steps of tln require energy?
``` synthesis of aa-tRNA initiation elongation release polypeptide proofreading ```
38
what does phosphorylation of eIF-2 do?
decreases rate of protein synthesis
39
What does eIF-2 do?
Carries GTP and initiator tRNA to ribosome
40
How does the regulation of globin synthesis in response to heme availability exemplify tln regulation?
- heme is absent --> eIF2 is phosphorylated by HCI = inactive - heme is present --> phosphate is removed, tln occurs
41
How is the 5'-cap involved in regulating euk tln?
- protects from nucleases - distinguishes btw mRNA and types of tRNA - eIFs recognize cap
42
How is the 5'-UTR involved in regulating euk tln?
sequences for translational efficiency
43
How is the 3'-UTR involved in regulating euk tln?
signal sequences so mRNA is translated in specific places in cell
44
How is the poly-A tail involved in regulating euk tln?
- stabilizes - important for lifespan of mRNA | - may catalyze formation of large ribosomal subunit
45
What feature of mRNA plays a huge role in tln regulation?
lifetime
46
what is a key regulatory molecule in tln of the ferritin/transferrin receptor?
aconitase
47
In what two ways does aconitase affect tln of the ferritin/transferrin receptor?
binds IRE 5'-UTR of ferritin mRNA --> blocks tln initiation | binds IRE 3'-UTR of ferritin mRNA --> stabilizes mRNA against degradation
48
what is the function of ferritin? What happens to the tln of ferritin if [iron] increases?
intracellular iron storage protein | increase [iron] increase tln of ferritin
49
what is the function of the transferrin receptor? What happens to the tln of transferrin receptor if [iron] increases?
imports iron | increase [iron] decrease tln of transferrin receptor
50
What is endogenous regulation of proteins synthesis?
siRNA pr miRNA can down-regulate tln by inducing mRNA degradation
51
What is exogenous regulation of protein synthesis?
dsRNA gets processed to siRNA --> degradation of mRNA
52
In what two ways can interferons work?
``` -inhibition of translation (makes protein kinase - phosphorylation of eEf-2) mRNA degradation (produces endoribonuclease --> mRNA non-functional) ```
53
How is an interferon produced?
- 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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