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UNION > BIO 205 TRANSLATION > Flashcards

BIO 205 TRANSLATION Flashcards

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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
aminoacyl-tRNAs
Transfer RNA + amino acids
26
tRNA is...
transfer RNA
27
f'n of tRNA
* adaptor molecules between transcription and translation | * recognizes the triplet code on the mRNA (codon)
28
codon
triplet code on the mRNA
29
``` AUG = codon ??? = anticodon ```
UAC
30
anticodon binds ---
5' ---> 3' | opposite of mRNA
31
secondary structure of tRNA
* 4 double-strand regions * cloverleaf * L-shaped
32
clover leaf shape
``` (AMINO ACID) | | | | | | (D-arm) (TYC-arm) | | | | (Anticodon) ```
33
tRNA location
``` polypeptide - tRNA (adaptor) - nucleic acid ```
34
charging of tRNA
* 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
tRNA wobbling
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
wobble proposed by
crick
37
where does wobble occur
@ 5' nucleotide of the tRNA anticodon ORRR • 3' nucleotide of the mRNA codon
38
most common wobble
U-G
39
how many stop codons
3
40
Characteristics of the genetic code
* triplet * comma free * non-overlapping * has start and stop signals * almost universal (not mitochondria euk) * degenerate * wobble
41
what 2 amino acids only code for one axon
Methionine (Met) | Tryptophan (Trp)
42
what are the stop codons
UAA UAG UGA
43
Eukaryotic Ribosomes made up of + prok ribosome
``` Large subunit (60s) + Small subunit (40s) ``` prok: large: 80s small: 70s
44
Eukaryotic Ribosomes are made up of:
1/3 proteins + 2/3 rRNAs
45
what do Large subunits in ribosomes do
catalyzes the formation of peptide bonds
46
what do small subunits in ribosomes do
matches the correct tRNA to codon on mRNA
47
binding sites on ribosomes
* mRNA binding site: small subunit * E-site * P-site * A-site
48
• E-site
exit-site
49
• P-site
peptide-site
50
• A-site
aminoacyl-site
51
what site "reads" new codon in mRNA
A-site
52
peptidyl transferase makes...
peptide bonds - Ribozyme
53
translation mechanism
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
3 overview steps in translation:
Initiation, elongation | and termination
55
How the translational machinery know which AUG to pay attention to?
PROKARYOTES: Shine-Delgarno sequence EUKARYOTES: Kozak consensus sequence
56
Shine-Delgarno sequence in...
prokaryotes
57
Kozak consensus sequence in...
eukaryotes
58
polycistronic mRNAs
in prokaryotes, multiple (Shine-Delgarno sequences) -- resulting in synthesis of a different protein
59
initiator tRNA in prokaryotes
modified fMet-tRNA
60
initiator tRNA in eukaryotes
tRNA^(fMet)
61
synthetase
responsible for attaching initator Met to tRNA molecules
62
INITIATION of protein synthesis STEPS:
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
ELONGATION
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
TERMINATION
* termination codon at A-site is recognized by release factors * release of polypeptide chain, dissociation of tRNA and mRNA
65
Polyribosomes (Polysomes)
euk: nucleus ---> cytoplasm prok: happens at same time
66
Antibiotics that block
Tetracycline, Steptomycin, Chloramphenicol, Cycloheximide, Rifamycin
67
Tetracycline
blocks binding of aminoacyl-tRNA to A-site of ribosome
68
Steptomycin
prevents transition from initiation complex to chain-elongating ribosome
69
Chloramphenicol
blocks peptidyl transferase reaction on ribosomes
70
Cycloheximide
blocks translocation reaction on ribosomes (large subunit)
71
Rifamycin
blocks initiation of RNA chain by binding to RNA polymerase
72
what is N-terminus & C-terminus
amino-terminus ; | carboxyl terminus

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