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Mbg 2040 > Genetic Code and Translation > Flashcards

Genetic Code and Translation Flashcards

1
Q

What is the order of transcription, translation, and mRNA degradation in prokaryotes

A

they are simultaneous occurrences

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1
Q

In eukaryotes where do transcription and translation occur

A

transcription - nucleus
translation - cytoplasm

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2
Q

Why does mRNA last longer in eukaryotes

A

in prokaryotes all steps occur in the same location simultaneously, in eukaryotes transcription and translation occur in different parts of the cell so mRNA exists for longer in eukaryotes

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3
Q

What researchers led to the “one gene one collinear protein” conclusion

A

Beadle and Tatum

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4
Q

What bond holds amino acids together

A

peptide bond (carboxyl of one bonded to amino of the other)

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5
Q

What code does the genetic code follow

A

triplet code
4^3 = 64 possible codons

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6
Q

How were codons discovered

A

homopolymers and copolymers were tested and were found to produce polypeptides with different amino acids

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7
Q

How many codons are there

A

64

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8
Q

How many of the 64 codons are stop codons

A

3

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9
Q

What does it mean when saying the genetic code is degenerate

A

some amino acids are specified by more than one codon

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10
Q

What 2 amino acids are specified by only one codon

A

methionine (start) and tryptophan

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11
Q

Why does degeneracy occur in the genetic code

A

the binding at the third codon position is flexible
- known as the wobble position

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12
Q

How does wobble occur in translation (think tRNA modification)

A

since tRNA can be modified at the nucleotide level, nucleotides can be substituted for other nucleotides and create wobble

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13
Q

What is the basics of the wobble hypothesis

A

nonstandard pairings can occur at the third position of a codon

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14
Q

What is a nickname for the ribosome

A

RNA machine - plays a role in protein synthesis, including the formation of peptide bonds between amino acids

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15
Q

What are the 4 important macromolecules of translation

A
  1. ribosomes
  2. amino acid activating enzymes
  3. tRNA molecules
  4. soluble proteins involved in initiation, elongation and termination
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16
Q

What is the function of aminoacyl tRNA synthetase

A

charges the tRNA molecule with its specific amino acid

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17
Q

What is the 2 step reaction between the amino acid and tRNA via aminoacyl tRNA synthetase

A
  1. amino acid reacts with ATP to our aminoacyl AMP
  2. amino acid is transferred to tRNA and AMP is released
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18
Q

How to tRNAs work

A

hold the anticodon for the codon of mRNA

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19
Q

What is another term for translation

A

protein synthesis

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20
Q

What is required to initiate translation

A

mRNA, large and small ribosomal subunits, initiation factors, and GTP

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21
Q

What is the initiation complex of translation in prokaryotes

A

Shine Dalgarno sequence

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22
Q

Where is the complement to the Shine dalgarno sequence held

A

in the 16S component of the 30S small ribosomal subunit

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23
Q

What is the Shine Dalgarno sequence

A

UAAGGAGGU

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24
Q

How does the small subunit bind first to prokaryotic mRNA in translation, without the binding of the large subunit

A

IF-3 binds to the large unit, preventing it from binding, causing only the small subunit to bind (has complementary sequence to Shine Dalgarno)

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25
Q

What positions fMet-tRNA over the start codon

A

IF-1 and IF-2

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26
Q

What makes up the 30S initiation complex

A

fMet-tRNA + 30S small subunit + IF2-GTP + IF-1 + IF-3

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27
Q

How does the large subunit then attach to the mRNA in prokaryotic translation initiation

A

IF-3 dissociates

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28
Q

How are the IF-2 and IF-1 factors dissociated from the initiation complex in prokaryotic translation

A

GTP is hydrolized into GDP and dissociates the remaining IF factors

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29
Q

What is the final complex at the start of prokaryotic translation called

A

the 70S complex (think of the overall subunits and complex of prokaryotic ribosomes)

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30
Q

What is the E site

A

exit site

31
Q

What is the P site

A

peptidyl site

32
Q

What is the A site

A

aminoacyl site

33
Q

What is the difference in methionine between prokaryotes and eukaryotes

A

prokaryotes = fMet
eukaryotes = Met (not formylated)

34
Q

What is the difference about the initiation complex location in prokaryotes and eukaryotes

A

prokaryotes = Shine Dalgarno
eukaryotes = initiation complex binds at 5’ cap and scans inwards to find first AUG codon

35
Q

What is the sequence involved in eukaryotic translation

A

Kozak sequence

36
Q

What is the purpose of the Kozak sequence

A

influence the efficiency of which AUG in the vicinity is used to begin translation

37
Q

What happens between the poly A tail and the 5’ cap structure in eukaryotic mRNA translation

A

the mRNA strand curls and proteins attached to the poly A tail interact with the proteins bound to the 5’ cap to create a cap binding protein complex

38
Q

What is the cap binding protein complex

A

when binding proteins on the poly A tail and binding proteins on the 5’ cap of eukaryotic mRNA interact during initiation of translation

39
Q

What is the Kozak sequence

A

5’ - C[A/G]NCAUG - 3’

40
Q

Where does fMet - tRNA first attach in translation elongation

A

the P site (skips A site)

41
Q

What two things come together to form a complex as the second tRNA molecule comes into translation elongation

A

Ef-Tu and GTP bind to charged tRNA to form a complex
- enters the A site of the ribosome (the second tRNA)

42
Q

What happens when the SECOND charged tRNA in elongation binds to the A site in translation

A

GTP is cleaved to GDP and the Ef-Tu complex is released

43
Q

Explain the basics of elongation in translation

A
  • first tRNA binds to the P site
  • second tRNA binds to Ef-Tu and GTP to form a complex, binds to the A site, and released the complex
  • peptide bond forms between the amino acids in the P and A sites
  • the ribosome moves down the mRNA strand to synthesize the amino acid chain

*tRNA moves from the A site to P site to E site (with the first tRNA starting at the P site)

44
Q

Where does tRNA go after being used in translation

A

released into cytoplasm

45
Q

What specifically in the large subunit catalyzes the formation of peptide bonds

A

rRNAs

45
Q

Which subunit catalyzes the peptide bond formation between amino acids

A

large subunit

46
Q

What is needed in order for translocation (movement of tRNA from one site to the next) to occur

A

the Ef-Tu GTP complex

47
Q

What does it mean for tRNA to be “charged”

A

has a bound amino acid

48
Q

What direction does the ribosome move along mRNA in translation

A

5’ - 3’

49
Q

In what direction does growth of the polypeptide occur

A

N-teminal to C-terminal

50
Q

Which site on the ribosome contains the growing peptide chain

A

the P site

51
Q

Are there notable differences in translation elongation between prokaryotes and eukaryotes

A

no - they are very similar

52
Q

When does termination occur in translation

A

when a stop codon is encountered at the A site of the ribosome

53
Q

Why does translation stop when a stop codon is encountered at the A site

A

because there are no corresponding tRNAs that match stop codons

54
Q

What happens when a stop codon is encountered instead of tRNA binding

A

a release factor binds (RF)

55
Q

What does RF-1 recognize

A

UAG and UAA

56
Q

What does RF-2 recognize

A

UAA and UGA

57
Q

What does the binding of RF-1 and RF-2 do to the translation process

A

alters the activity of peptidyl transferase and the amino acid chain is released, termination translation

58
Q

What factors assist in dismantling the ribosomal complex in translation post termination

A

RF-3 and GTP

59
Q

What is the difference between prokaryotic and eukaryotic termination of translation

A

they are very similar
- release factors are symbolized as eRF-1 and eRF-2 in eukaryotes

60
Q

What enzyme attaches amino acids to tRNAs in tRNA charging of translation

A

aminoacyl-tRNA synthetases

61
Q

What is the energy source used to bind amino acids to tRNAs

A

ATP

62
Q

What is the function of elongation factor Tu

A

binds GTP and charged tRNA - brings charged tRNA to A site on ribosome

63
Q

What is the function of elongation factor Ts

A

regenerates active elongation factor Tu

64
Q

What is the function of elongation factor G

A

stimulates translocation of ribosome to next codon

65
Q

What is the function of GTP

A

provides energy

66
Q

What is the function of the 23S rRNA in the large ribosomal subunit

A

form peptide bonds between amino acids in the P and A sites

67
Q

What step of translation does chloromycetin inhibit

A

formation of peptide bonds

68
Q

What step of translation does erythromycin inhibit

A

translocation of mRNA along ribosome

69
Q

What step of translation does neomycin inhibit

A

interactions between tRNA and mRNA

70
Q

What step of translation does streptomycin inhibit

A

initiation of translation

71
Q

What step of translation does tetracycline inhibit

A

binding of tRNA to ribosome

72
Q

What step of translation does paromomycin inhibit

A

validation of mRNA-tRNA match

73
Q

What are some neurological diseases associated with translation

A

amyotrophic lateral sclerosis
frontotemproal dementia
spinal musclar atrophy
alzheimers
parkinsons
huntingtons
autism
down syndrome

Mbg 2040 (13 decks)

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