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Protein Synthesis Flashcards

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1
Q

Structure of tRNA

A

75 bases
50% bases base paired
10% modified bases

Acceptor stem, T loop, anticodon loop, D loop, variable loop

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2
Q

D Loop

A

Interacts with the synthetase enzymes

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3
Q

Acceptor Stem

A

Site of amino acid charging by the synthetase enzymes

Always has conserved sequence: CCA

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4
Q

T Loop

A

Interacts with 5S rRNA, helps position tRNA in the ribosome

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5
Q

How are bacterial tRNAs synthesized?

A
  • Multimeric: 2 or more tRNAs in a transcript, which are processed to monomeric precursors; may also be embedded in rRNA transcripts
  • cleaved by RNases at 5’ and 3’ ends
  • bases modified
  • CCA added to 3’ end by tRNA nucleotidyl transferase (if not present already)
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6
Q

Processing of prokaryotic tRNA transcripts (multimers)

A
  1. 5’ end cleavage by RNase
  2. 3’ end cleavage by RNase
  3. Bases modified
  4. CCA added
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7
Q

Eukaryotic

A

Made as monomeric precursors
Leader sequence on 5’ end is cleaved off
There is an intron by the anticodon which masks it –> tRNA cannot be used until fully processed/modified

Removal of tRNA intron involves endonuclease cleavage and ATP-dependent ligation

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8
Q

Prokaryotic Ribosome

A

50S- 23S + 5S rRNA
30S- 16S rRNA

70S

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9
Q

Eukaryotic Ribosome

A

60S- 28S + 5.8S rRNA
40S- 18S rRNA

80S

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10
Q

Processing rRNA

A

Transcribed by Pol I- moderately repetitive sequences
Self splicing ribozymes (no need for snRNPs)
Pol II brings in 5S rRNA

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11
Q

Where in the cell do ribosomal subunits self assemble from rRNAs and ribosomal proteins?

A

Nucleolus

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12
Q

Wobble sequence

A

Base pairing between codon/anticodon in 5’ and middle codon bases must be perfect

Some flexibility in 3’ base of codon (5’ anticodon)

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13
Q

What does bacterial protein synthesis require?

A

mRNA (read 5’ –> 3’)

Ribosomes (subunits assemble on the mRNA)

Protein factors for initiation elongation, and termination

Activated tRNAs: one or more for each amino acid

Unique tRNA for initiation (f-met-tRNA)

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14
Q

Which translational protein factors require GTP energy?

A

IF2-GTP: to bind Met-tRNA

EF-Tu-GTP: Delivery of aminoacyl tRNA to ribosomes
EF-G-GTP: Translocation factors
RF-3-GTP: Release of complete polypeptide chain

eiF2-GTP (eukaryotes): Helps bind Met-tRNA

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15
Q

What does it mean that tRNA are adaptor molecules?

A

Bind both amino acids and mRNA codons

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16
Q

Function of aminoacyl tRNA synthetases

A

Activation of amino acids prior to tRNA attachment

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17
Q

2 steps in Amino Acid activation

A

Amino acid + ATP —-> aminoacyl adenylate: synthetase + PPi

Aminoacyl adenylate: synthetase + tRNA —> aminoacyl-tRNA: synthetase + AMP

SUM: AA + ATP + tRNA —> AA-tRNA + AMP + PPi

1) both carried out by aminoacyl tRNA synthetase
2) Synthetase specific for a given amino acid (ie: alanine tRNA synthetase)

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18
Q

How does synthetase control accuracy?

A

1) Each synthetase must recognize R group on amino acid AND some part of the nucelotide sequence of the corresponding tRNA (either anticodon, specific sequence on acceptor stem, sequences somewhere else on the molecule)
2) Each synthetase has an activation site (for activation and attachment) and a hydrolytic site to correct errors
3) The aa-tRNA complex that leaves the synthetase will be used in protein synthesis with no further means of correcting errors

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19
Q

How many energy bonds cleaves during aa activation?

A

Two high energy bonds cleaved/ aa activated- protein synthesis requires energy

1) cleavage of ATP
2) subsequent hydrolysis of pyrophosphate

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20
Q

Initiation of protein synthesis in prokaryotes

A

1) Formyl group added to met. Complex of initiator tRNA bound to fmet and IF2-GTP

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21
Q

First Codon in Prokaryotes

A

AUG

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22
Q

How to locate first codon (P)

Study These Flashcards
A

Shine Dalgarno sequence

23
Q

First amino acid (P)

24
Q

Initiation factor (P)

25
Small subunit binding codon (P)
AUG
26
Ribosome assembly codon (P)
AUG
27
Elongation (P)
EF-Tu-GTP, peptidyl transferase, EF-G-GTP cycle
28
Termination (P)
Stop codon/RF-GTP protein
29
Shine Dalgarno Sequence
purine rich sequence: base pairs with 3' end of 16S rRNA. Usually 7-10 bases upstream of AUG start codon AUG start codon is not necessarily the 1st AUG, but the AUG closest to the Shine Dalgarno Sequence
30
Elongation: Repeat of 3 Steps (P)
1) Codon-specific binding of the aminoacyl-tRNA to the A site of the ribosome mediated by EF-Tu-GTP
31
Polyribosome
Complex of mRNA with multiple ribosomes called a polyribosome or polysome Once the start codon is free, another round of initiation can begin --> many ribosomes can read mRNA at the same time
32
Translation + Transcription
mRNA is read in translation from 5' --> 3' and is synthesized from 5' --> 3' Therefore can be translated while being synthesized
33
Termination of Protein synthesis in prokaryotes
1) Stop codons: UAA, UAG, UGA appears in the A site 2) Stop codon recognized by RF1 and RF2 and they bind near the site so nothing else can come in 3) RF3-GTP binds ribosome 4) Hydrolysis of GTP 5) Cleavage of Ester bond (peptidyl transferase) 6) Release of protein, tRNA, mRNA, ribosomal subunits
34
Tetracycline
Inhibitor of Protein Synthesis | Blocks binding of aminoacyl-tRNA to A-site of ribosome (prokaryotes only)
35
Chloramphenicol
Inhibitor of Protein Synthesis | Resembles peptide bond; inhibits pepitdyl transferase activity (prokaryotes only)
36
Initiation of Translation differences between Eukaryotes and Prokaryotes
- capped mRNA - initiation factors: eIF for eukaryotic - met-tRNA is not formylated - Ribosomal subunit/met-initiator tRNA/factors scan along mRNA to find AUG start codon- no Shine Dalgarno
37
First Codon (E)
AUG
38
How is first codon located (E)
Kozak Sequence
39
First amino acid (E)
Met
40
Where does the small subunit bind to? (E)
At the cap
41
Where does the ribosome assemble? (E)
AUG codon
42
Where is termination? (E)
Stop Codon/ RF protein
43
eIF4F
eIF4A-helicase eIF4B- ATPase eIF4E- binds eIF3 (on 40S ribosomal subunit) *cap binding proteins*
44
eIF4G
scaffold protein on the cap
45
Kozak Sequence
Contains the first AUG after the AUG at the cap
46
Eukaryotic Translation
1) 5' cap interacts with the cap binding complex (A,B,E) 2) Presence of the eIF4F facilitates binding of the small-subunit tRNA 3) eIF4E facilitates binding of small subunit eIF3 initiator tRNA-eIF2-GTP (binds eIF3) 4) eIF4A (helicase), eIF4B (ATPase) move ahead to unwind secondary structure 5) small subunit eIF3-initiator tRNA eIF2 GTP scans the mRNA w/ the 40S subunit to find the AUG initiation codon (in Kozak consensus) 6) eIF5 then causes release of these accessory factors, GTP mediated re-organization and joining of the large subunit
47
Loop structure on Eukaroytic mRNA
Facilitates ribosome recycling Cap binding proteins interact with Poly A binding proteins
48
HCV vs HIV
HCV - RNA virus- flavivirus - Infects liver cells - uses host ribosomes to synthesize viral proteins but not into host DNA HIV - RNA virus- retrovirus - infects human immune cells - uses host DNA and genetic material to replicate
49
Lifecycle of HCV
(+) RNA virus infects cells and conducts translation with RNA-dependent RNA polymerase 5A is a replication protein on cell ER and 5B is a RNA-dependent RNA polymerase on cell ER Using those proteins, create (-) RNA Change back to (+) RNA Now can infect other cells
50
Ledipasvir
inhibits NS5A- replication complex protein
51
Sofosbuvir
inhibits NS5B- RNA dependent RNA polymerase (
52
If HCV RNA (+) is not capped, how can it be translated by the host ribosomes?
HCV IRES Internal ribosome entry sequence IRES is recognized by 40S subunit and eIF3 complex some how
53
Ataluren-Facilitated Translation
Ataluren is a drug to help with CF mutation class 1 with shortened protein Drug helps shift ribosome, tRNA-trp binds to stop codon --> still can get same length protein as opposed to before when the trp could not bind to stop codon

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