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Molecular 3rd pt. 2 > Lecture 3 > Flashcards

Lecture 3 Flashcards

1
Q

protein synthesis goes in what direction

A

N terminal to C terminal

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2
Q

what is the start codon

A

AUG (makes met)

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3
Q

AUG/ met turns into what terminal of a protein

A

N terminal

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4
Q

where will the peptide bond form between two AA

A

will lose H2O

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5
Q

how long are tRNAs

A

70-90 nucleotides long

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6
Q

what structure does tRNA have

A

2D structure resembling a cloverleaf

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7
Q

what is the role of tRNA

A
  • to act as an adaptor
  • to bring the correct AA specified by the codon on the mRNA
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8
Q

what does the trident mean here

A
  • the location is “psi”
  • this is the most common modification
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9
Q

true/false the anticodon is complementary to the codon

A

true

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10
Q

true/false the anticodon is the same sequence as the codon

A

false

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11
Q

what loops are present on the cloverleaf structure of the tRNA

A
  • T loop
  • anticodon loop
  • D loop
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12
Q

true/false the accuracy of attaching AA to tRNA is very accurate

A

true

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13
Q

what end is this

A

3’ end of tRNA

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14
Q

the process of linking an activated AA to a tRNA is also referred to as what

A

tRNA charging

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15
Q

the energy in this bond is used for what

A
  • to incorporate the NEXT AA to the polypeptide chain
  • not the current one
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16
Q

how many aminoacyl-tRNA synthetases are there

A
  • 20
  • one for each AA
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17
Q

how many subunits in ribosomes

A

2 (large and small)

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18
Q

what does the small subunit of a ribosome do

A

binds the tRNAs and mRNA

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19
Q

what does the large subunit of a ribosome do

A
  • binds the tRNAs
  • catalyzes peptide bond formation
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20
Q

rRNAs are ______ (more/less) highly conserved than the ribosomal proteins

A

more

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21
Q

what does SSu rRNAs stand for

A

small subunit rRNAs

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22
Q

sequence comparison of SSu rRNAs from diff organisms are commonly used for what

A

construction of phylogenic trees

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23
Q

how many binding sites are in the ribosome for mRNA

A

1

24
Q

how many binding sites are in the ribosome for tRNA

A

3

25
Q

how many tRNAs can be bound on the ribosome at the same time

A

2

26
Q

the tRNA that is connected to the polypeptide chain is at which site

A

P site

27
Q

what are the diff binding sites of the ribosome

A

EPA

28
Q

what are the steps included in translation of mRNA

A
  • incoming Aminoacyl-tRNA binds to A-site
  • peptide bond forms with the AA in the P site (which is attached to the pre-existing polypeptide chain)
  • the large subunit moved over one codon. so now tRNA 3 is at hybrid site EP and tRNA 4 is at hybrid site PA
  • basically the tRNAs stay in place, just the EPA binding sites move over one so they aren’t in the spot they were before
  • the large and small subunits are aligned anymore so the small shifts over to align with large
  • this means the ribosome is “reset”
  • now A site is free for a new tRNA
29
Q

when do tRNAs dissociate from the E-site

A
  • once the small subunit shifts over, resetting the ribosome
  • when the tRNA goes from E/P hybrid site to just E
30
Q

true/false the ribosome picks which AUG is the right to follow the same way in prokaryotes and eukaryotes

A
  • false
  • they’re diff mechanisms
31
Q

how does the ribosome picks which AUG is the right to follow in prokaryotes

A
  • usine shine-dalgarno sequence
  • should be about 10 nucleotides upstread of AUG
  • the other (wrong) AUGs won’t have them, so the ribosome knows they’re wrong
32
Q

how does the shine-dalgarno sequene work

A

its complementary to the 3’ end of the 16s rRNA within the small subunit of the ribosome

33
Q

what are polycistronic mRNA

A

contains coding regions for diff proteins

34
Q

what is an example of polycistronic mRNA

A

the lac operon

35
Q

prokaryotic ribosomes assembling directly on AUG codon within interior of mRNA allows for translation of what

A

polycistronic mRNA

36
Q

what are added to eukaryotic mRNA post transcription

A
  • 5’ cap
  • 3’ polyA tail
37
Q

how to ribosomes bind to eukaryotic mRNA

A
  • small subunit binds to 5’ cap
  • start scanning 5’ to 3’ until they reach the first AUG
  • 90% of the time, they start translation at this first AUG
38
Q

what is the preferred translation start in eukaryotic mRNA

A

ideally there will be a Kozak sequence surrounding the 1st AUG

39
Q

what happens in eukaryotic mRNA is a kozak sequence is missing

A
  • “leaking scanning”
  • an AUG codon further downstream would be chosen for translation start
40
Q

where does “ribosome scanning” mechanisms occur

A

translation initiation in eukaryotes

41
Q

10% of the nucleotides within tRNA molecules are modified how

A

by covalent modifications

42
Q

how does covalent modifications done to nucleotides within tRNA affect it

A
  • promotes intramolecular basepairings
  • this stabilizes tRNA structure
  • helps tRNAs recognize correct AA and mRNA codon
43
Q

what is important in wobble basepairing

A

isonine

44
Q

what is the difference between uridine and pseudouridine

A

modified nucleotide (Ψ) found in cellular tRNA (and rRNA, snRNA, snoRNA)

45
Q

what is the difference between pseudouridine and N1-Methylpesuedouridine

A

chemically modified pseudouridine in mRNA made for COVID vaccine

46
Q

what did the 2023 nobel prize in physiology or medicine do

A
  • the use of pseudouridine to stabilize and reduce cellular toxicity of in vitro transcribed mRNA
  • tRNA will survive by mRNA won’t, so they found the major difference was in the modification of uridine
47
Q

why do stop codons stop

A
  • cause it doesn’t have a complementary tRNA or antidocon
  • once it reaches there, they bring in water instead of tRNA cause there is no tRNA for it
48
Q

true/false the genetic code is redundant

A

true

49
Q

how many diff tRNAs are needed to recognize the 4 glycine codons

A

3

50
Q

how can a tRNA recognize more than one codon

A

through wobble base pairing

51
Q

how does wobble base pairing occur

A
  • according to a list, for each nucleotide in the third position of the codon, there are possible different nucleotides that can be there that can still code for the same tRNA
  • this happens often with isonine
  • the bonds will be weaker than typical base pairs
52
Q

when does isonine form

A

the deamination of adenosine

53
Q

what is needed for the reaction in which two AA are attached to each other (ie, if they’re not there, AA cannot be added and proteins cant be formed)

A
  • 2 AA
  • ATP
54
Q

how are AA attached to tRNA

A
  • ATP hydrolysis happens, producing energy
  • AA will be “activated” by attaching its carboxyl group to AMP
  • this makes an adenylated AA
  • the AMP then switches places kinda with the 3’ end of the tRNA molecule
  • the AMP goes away
55
Q
A

Molecular 3rd pt. 2 (12 decks)

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