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UNION > BIO 205 TRANSLATION > Flashcards

BIO 205 TRANSLATION Flashcards

1
Q

differences between prokaryotic and eukaryotic mRNA

A

PROK: multiple translation start sites – many proteins
EUK: single start site – one protein

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2
Q

Translation machinery is __% of dry weight of cell

A

35

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3
Q

where does protein synthesis occur

A

on ribosome

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4
Q

mRNA code is read:

A

from 5’ to 3’

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5
Q

protein is synthesized: what terminus’

A

N-terminus to C-terminus

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6
Q

how many amino acids to code for

A

20

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7
Q

There are _ possibilities at each nucleotide “position” of the codon

A

4

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8
Q

minimum # of nucleotides in a codon

A

3 letters

64 words

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9
Q

codon is how many nucleotides

A

3

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10
Q

Nirenberg wanted to discover

A

how proteins could be synthesized from DNA

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11
Q

Nirenberg experiment

A 
bacterial extract 
\+ 
single-nucleotide synthetic mRNA
[UUU][UUU][UUU]
=
synthesized polypeptide
[Phe][Phe][Phe]
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12
Q

The genetic code is a __ triplet code

A

non-overlapping

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13
Q

Non-overlapping
versus.
overlapping

A

non: 1 amino acid changed (observed)

over lapping: 3 changed (not observed)

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14
Q

genetic code is degenerate because

A

an amino acid can be encoded by several codons

- 18 amino acids coded by more than 1 codon

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15
Q

three possible reading frames …..

A
  • one 1 “true” open reading frame (ORF)

* 3 neg reading frames

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16
Q

ORF

A

open reading frame

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17
Q

How does the cell know which reading frame is correct?

A

presence of the first AUG (encodes Met: methionine)

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18
Q

what does ribosome do when it binds to 5’ cap

A

looks for amino acid AUG

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19
Q

missense mutation

A

• replacement/
substitution
• nucleotide change – new amino acid

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20
Q

if incorrect nucleotide, why is it okay

A

many code for same amino acid

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21
Q

nonsense mutation

A

incorrect sequences cause all code to stop

- protein shortens

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22
Q

frameshift mutation

A
  • insert/deletion
  • changes entire sequence
  • not drastic if 3 nucleotides removed
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23
Q

Ingredients in

translation:

A 
1- mRNA
2-Transfer RNA + amino acids (aminoacyl-tRNAs)
3- Ribosomes
4- Initiation, elongation 
and release factors + energy (GTP)
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24
Q

translation aka:

A

protein synthesis

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25
Q

aminoacyl-tRNAs

A

Transfer RNA + amino acids

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26
Q

tRNA is…

A

transfer RNA

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27
Q

f’n of tRNA

A
  • adaptor molecules between transcription and translation

* recognizes the triplet code on the mRNA (codon)

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28
Q

codon

A

triplet code on the mRNA

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29
Q 
AUG = codon
??? = anticodon
A

UAC

30
Q

anticodon binds —

A

5’ —> 3’

opposite of mRNA

31
Q

secondary structure of tRNA

A
  • 4 double-strand regions
  • cloverleaf
  • L-shaped
32
Q

clover leaf shape

A 
(AMINO ACID)
                     | |
                     | |
                     | |
(D-arm)                 (TYC-arm)
                     | |
                     | |
             (Anticodon)
33
Q

tRNA location

A 
polypeptide
-
tRNA (adaptor)
- 
nucleic acid
34
Q

charging of tRNA

A
  • amino acid first must attach to tRNA
  • (enzyme) aminoacyl-tRNA-synthetase recognizes and attaches correct AMINO ACID to tRNA molecule
  • then dissociates
  • requires ATP
  • charged tRNA will then carry activated amino acid to ribosome
35
Q

tRNA wobbling

A

ability of tRNA to recognize two or three different mRNA codons
• some tRNAs can tolerate a mismatch at @ 3rd position of codon
• explains why there’s so many codon variations for amino acids

36
Q

wobble proposed by

A

crick

37
Q

where does wobble occur

A

@ 5’ nucleotide of the tRNA anticodon
ORRR
• 3’ nucleotide of the mRNA codon

38
Q

most common wobble

A

U-G

39
Q

how many stop codons

A

3

40
Q

Characteristics of the genetic code

A
  • triplet
  • comma free
  • non-overlapping
  • has start and stop signals
  • almost universal (not mitochondria euk)
  • degenerate
  • wobble
41
Q

what 2 amino acids only code for one axon

A

Methionine (Met)

Tryptophan (Trp)

42
Q

what are the stop codons

A

UAA
UAG
UGA

43
Q

Eukaryotic Ribosomes made up of

+ prok ribosome

A 
Large subunit (60s)
\+ 
Small subunit (40s)

prok: large: 80s
small: 70s

44
Q

Eukaryotic Ribosomes are made up of:

A

1/3 proteins + 2/3 rRNAs

45
Q

what do Large subunits in ribosomes do

A

catalyzes the formation of peptide bonds

46
Q

what do small subunits in ribosomes do

A

matches the correct tRNA to codon on mRNA

47
Q

binding sites on ribosomes

A
  • mRNA binding site: small subunit
  • E-site
  • P-site
  • A-site
48
Q

• E-site

A

exit-site

49
Q

• P-site

A

peptide-site

50
Q

• A-site

A

aminoacyl-site

51
Q

what site “reads” new codon in mRNA

A

A-site

52
Q

peptidyl transferase makes…

A

peptide bonds - Ribozyme

53
Q

translation mechanism

A

1- ribosome binds mRNA at start codon
2- polypeptide chain elongates by successively adding amino acids
3- @ stop codon, polypeptide is released and ribosome dissociates

54
Q

3 overview steps in translation:

A

Initiation, elongation

and termination

55
Q

How the translational machinery know which AUG to pay attention to?

A

PROKARYOTES: Shine-Delgarno sequence
EUKARYOTES: Kozak consensus sequence

56
Q

Shine-Delgarno sequence in…

A

prokaryotes

57
Q

Kozak consensus sequence in…

A

eukaryotes

58
Q

polycistronic mRNAs

A

in prokaryotes, multiple (Shine-Delgarno sequences) – resulting in synthesis of a different protein

59
Q

initiator tRNA in prokaryotes

A

modified fMet-tRNA

60
Q

initiator tRNA in eukaryotes

A

tRNA^(fMet)

61
Q

synthetase

A

responsible for attaching initator Met to tRNA molecules

62
Q

INITIATION of protein synthesis STEPS:

A

1- initiator tRNA on small subunit (with initiation factors bound)
2- binds to mRNA @5’ end
3- initiator tRNA moves along RNA to find 1st AUG
4- initiation factors dissociate
5- large ribosomal subunit binds to small
• forms RIBOSOME
6- aminoacyl-tRNA binds to A-site
7- peptide bond forms

63
Q

ELONGATION

A

1- newly bound charged tRNA binds to A-site
2- peptide transferase connectes amino acids on polypeptide bond
3- large subunit translocates –>
4- small subunit moves –>
• A-site tRNA now moved to P, P moved to E
5- uncharged tRNA (left over) now at A, is ejected from E-site
6- new bound charged tRNA binds to A-site

64
Q

TERMINATION

A
  • termination codon at A-site is recognized by release factors
  • release of polypeptide chain, dissociation of tRNA and mRNA
65
Q

Polyribosomes (Polysomes)

A

euk: nucleus —> cytoplasm
prok: happens at same time

66
Q

Antibiotics that block

A

Tetracycline, Steptomycin, Chloramphenicol, Cycloheximide, Rifamycin

67
Q

Tetracycline

A

blocks binding of aminoacyl-tRNA to A-site of ribosome

68
Q

Steptomycin

A

prevents transition from initiation complex to chain-elongating ribosome

69
Q

Chloramphenicol

A

blocks peptidyl transferase reaction on ribosomes

70
Q

Cycloheximide

A

blocks translocation reaction on ribosomes (large subunit)

71
Q

Rifamycin

A

blocks initiation of RNA chain by binding to RNA polymerase

72
Q

what is N-terminus & C-terminus

A

amino-terminus ;

carboxyl terminus

UNION (10 decks)

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