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Medical Biochemistry > Protein Synthesis-- Translation from RNA to Protein > Flashcards

Protein Synthesis-- Translation from RNA to Protein Flashcards

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USMLE® Step 1 flashcards
1
Q

Why study protein synthesis?

A
  • last opportunity for regulating gene expression
  • rapid response to stimuli (transcription sometimes takes too long b/c in the nucleus)
  • many pharmaceutics impact translation (i.e. antibiotics)
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2
Q

STOP codons

A

UAA (U Are Annoying)
UGA (U Go Away)
UAG (U Are Gone)

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3
Q

START codon

A

AUG (Methionine)

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4
Q

Nonsense Mutiation

A

STOP speaking that nonsense

mutation creating stop codon

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5
Q

Key Players in Translation

A
  • mRNA: the code
  • tRNA: the adapter
  • the ribosome: the enzyme
  • *** Above ONLY NEEDED for protein synthesis **
  • factors: the multitude of proteins that make the system work (increase efficiency, but are not necessary for occurrence)
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6
Q

5’ cap

A
  • specialized nucleotide that is required for BINDING OF INITIATION FACTORS
  • stability
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7
Q

5’ UTR

A

sequence between 5’ cap and the initiation codon

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8
Q

Coding Region

A

sequence that gets translated into protein

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9
Q

3’ UTR

A
  • sequence between the stop codon and the poly(A) tail

- site of key regulatory sequences

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10
Q

poly(A) tail

A

untemplated polyadenylate sequence averaging ~200 nucleotides that protects mRNA from degradation and increases translational efficiency

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11
Q

5’ UTR

3’ UTR

A

5’ UTR: regulation; non-coding

3’ UTR: regulation; non-coding; stability

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12
Q

Aminoacylation

A

AA added to 3’

  • enzymes (aminoacyl tRNA synthetases) recognize tRNAs and add appropriate AA
  • requires ATP
  • ** ACTIVATION; HIGH ENERGY BOND FORMED via AMP; AA attached to 3’ end ***
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13
Q

Translational Fidelity

Synthesis site vs Editing site

A

identifies anticodon loop (only proper loop will fit in enzyme; SPECIFICITY OF SHAPE AND CHARGE)

  • synthesis site: v high affinity for proper AA; if incorrect cannot access site unless similar in size and structure
  • editing site: v high affinity for INCORRECT AA; if enters editing site it will be cleaved off
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14
Q

Anticodon Loop

A
  • recognizes codon
  • aminoacylation adds proper AA to 3’ end of tRNA
  • ATP driven
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15
Q

Ribosome = Ribozyme

A

rRNA is sufficient to carry out protein formation; it is an enzyme but poor efficiency w/o additional enzymes

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16
Q

Ribosome Binding Sites

A

A (aminoacyl): initial tRNA binding site for next codon
P (peptidyl): peptide bond formation
E (exit): tRNA release

Attach’ Put on bond; Exit

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17
Q

Translation Cycle

A

Initiation (Initiation Factor)
Elongation (Elongation Factor)
Termination (RELIEF Factor)

Initiation and Elongation occur at the same time with different ribosomes

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18
Q

Polyzome

A

mRNA + multiple ribosomes

mRNA ribosome complex

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19
Q

Initiation

A
  • assembly of ribosome and mRNA

- positioning of the ribosome on the start codon (AUG)

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20
Q

Where does initiator tRNA enter at?

A

tRNA-MET enters at P site; all others enter at A site

** INITIATION tRNA DIFF THAN NORMAL MET tRNA (different one used during elongation) **

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21
Q

eIF4E

A

Initiation

binds to the 5’ cap; recruits eIF4G

22
Q

eIF2

A

Initiation

binds and delivers initiator Met-tRNA (requires GTP)

23
Q

eIF4G

A

Initiation
scaffold protein that binds eIF4E; required for assembly of pre-initiation complex
- bound at 5’ end and interacts with 3’ end creating circular mRNA allowing subunit to attach

24
Q

Large subunit attachment

A

small subunit attaches post circularization of mRNA; once attached will scan for AUG codon; once reaches AUG large unit will come and attach

25
Q

eIF2 release

A

(eIF2 binds and delivers intiation Met-tRNA to P site)
GTP hydrolysis cause eIF2 release
- once released large subunit attaches

26
Q

Elongation

A

movement of the ribosome down the mRNA coordinated with aminoacyl tRNA delivery

27
Q

rRNA site Occupation

A

at any given time only TWO SITES OCCUPIED

28
Q

Initiation Steps Overview

A

1) formation of pre-initiation complex

2) Scanning to AUG codon

29
Q

Elongation Steps Overview

A

1) delivery of aa-tRNA to A site and E site release
2) GTP hydrolysis and eEF1A release
3) eEF2 binding to catalyze translocation
4) GTP hydrolysis and eEF2 release; completion of cycle

30
Q

eEF1A

A

Elongation

binds all cononical tRNAs (all except initiator and selenocysteine tRNA)

31
Q

GTP hydrolysis is required

A

for release and promoting next step

32
Q

eEF2

A

Elongation

  • drags along large subunit; small unit follows; movement allows for elongation
  • G-protein required for ribosome translocation
  • if eEF2 is affected TRANSLOCATION CANNOT OCCUR, thus A site will never be empty and translation cannot proceed
33
Q

“Proofreading” during Elongation

A

occurs in the ribosomal A-site where codon/anticodon pairs are “checked” by ribosome conformation
- incorrectly base-paired tRNAs preferentially dissociate

34
Q

Termination

A

eRF2 binding and peptide hydrolysis

35
Q

eRF1

A
  • attaches and terminates protein synthesis
  • recruited when STOP codon is recognized
  • ** NO tRNA for STOP codons *** (tRAN mimetic and catalyzes release of completed peptide)
36
Q

terminator tRNA

A

DOES NOT EXIST

37
Q

Shine-Delgarno sequence

A
  • initiation in prokaryotes
  • upstream of start codon
  • directly pairs to rRNA
38
Q

Bacterial ribosomes allow for SELECTIVE inhibition by the ribosome inhibitor class of antibiotics

A

True

39
Q

Mitochondrial Ribosomes

A

similar to bacterial ribosomes

- ribosome inhibitors have residual toxicity due to this similarity

40
Q 
Eukaryote vs Prokaryote
Eukaryote
- monocistronic mRNA
- 40, 60, 80S ribosome
- eIF4E
- eIF2
- eIF4G
- eEF1A
- eEF2
A

Prokaryote

  • polycistronic
  • 30, 50, 70S ribosome
  • eIF4E = no counterpart
  • eIF2 = IF2
  • eIF4G = no counterpart
  • eEF1A = EFTu
  • eEF2 = EFG
41
Q

Hypoxia Regulation

A
  • mTOR signaling pathway represses translation in response to hypoxia by regulating the function of eIF4E
  • the mTOR pathway up-regulates during growth and down-regulates during stress
42
Q

4EBPs

A
  • increased affinity for eIF4E; binds and inhibits translation
  • when phosphorylated they are released from eIF4E and translation inhibition is relieved
43
Q

4EBP phosphorylation regulator

A

mTOR pathway; activation causes 4EBP phosphorylation and increases translation

44
Q

mTOR repression
mTOR “normal”
mTOR high

A

repression: hypoxia; dephosphorylated, decreased translation
normal: normal phosphorylation, normal translation
high mTOR: response to growth stimulus or uncontrolled growth (cancer)

45
Q

21st AA

A

Selenocysteine

  • AUG codon (NOT stop); codon “re-coded” by SBP2
  • cysteine with selenol instead of thiol
46
Q

Hyperthyroidism

A

caused by selenocysteine deficiency

47
Q

Diptheria toxin

A

shuts down translation by modifying the elongation factor responsible for translocation (eEF2)

48
Q

Deiodinases

A

selenoproteins required for thyroid hormone maturation

DIO1-2-3

49
Q

SBP2

A

protein required for recoding UGA to selenocyteine codon

50
Q

EF1A and selenocysteine

A

EF1A delivers all tRNA to A site EXCEPT selenocysteine

-eEFSec only protein which can deliver selenocysteine to A site

51
Q

SECIS

A

HOW mRNA KNOWS IF UGA IS STOP OR SELENOCYSTEINE

  • when present UGA=> selenocysteine
  • SBP2 binds exclusively to selenocysteine

Medical Biochemistry (7 decks)

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