Chapter 6: Translation

Question 1

How many codons go for the each base triplets?

Answer 1

• 3 letter codons

Question 2

The large ribosomal subunit ensures what?

Answer 2

• that the reading frame is correct

Question 3

AUG codon is what in eukaryotes?Prokaryotes?

Answer 3

• STARTING CODON …MET in eukaryotes

- FMET in bacteria

Question 4

UAG codon is the ___ codon??? How many?

Answer 4

• stop codon
  -3
  L> UAA, UAG , UGA …they al code for a release factor

Question 5

tRNA specifics:

- Amnioacyl tRNA synthetase??

Answer 5

• attaches the correct aa to tRNA

Question 6

tRNA specifics:

- Aminoacylation?

Answer 6

• process of attaching the correct aa to tRNA

20 enzymes?

Question 7

Ribosomal Details:

- three sites what are they?

Answer 7

• A site
• P site
• E site

Question 8

Ribosomal Details:

1. A site??
2. P site???
3. E site??

Answer 8

1. Amnioacyl-tRNA binds here, where tRNA brings in the aa …fresh one
2. Peptidyl-tRNA location …where the growing polypeptide chain is! peptide bonds form
3. Empty tRNA ..uncharged tRNA. … where tRNA binds on its path from the p site leaving the ribosome.

Question 9

Ribosomal Details:

- aa’s are let go from the p site and they attach to what site?

Answer 9

• A site….where there originally was only one amino acid….and stays there for a short time
  L> translocation occurs and the ribosomal subunit moves…it now has a new A site and a fresh charge tRNA comes in

Question 10

Initiation of Translation (Prokaryotes):

- AUG of mRNA binds to the _____???

Answer 10

• small ribosomal sub unit

Question 11

Initiation of Translation (Prokaryotes):
- AUG of mRNA binds to the small ribosomal subunit…..
L> Initiation factors??

Answer 11

• IF1, IF2 and IF3 ( prokaryote IF’s)

Question 12

Initiation of Translation (Prokaryotes):

• AUG of mRNA binds to the small ribosomal subunit…..
• Shine Delgarno sequence??

Answer 12

• upstream from the start codon close to the 5’ cap…it helps the small Ribosomal subunit bind

Question 13

Initiation of Translation (Prokaryotes):
- AUG of mRNA binds to the small ribosomal subunit…..
L> Does anything occur to the codons that are upstream from the start codon?

Answer 13

NO

Question 14

Initiation of Translation (Prokaryotes):

• AUG of mRNA binds to the small ribosomal subunit…..
• The initiator ___ binds to the AUG now??

Answer 14

• tRNA….fMET in bacteria

anticodon ( 5’ CAU 3’

Question 15

Initiation of Translation (Prokaryotes):
- AUG of mRNA binds to the small ribosomal subunit…..
L> the next step after the initiator tRNA binds is??

Answer 15

• the large ribosomal subunit binds!

Question 16

Initiation of Translation (Prokaryotes):
Initiation Factors....GO
IF-1
IF-2 
IF-3

Answer 16

1. prevents initiator tRNA from binding to the wrong site on the small RSU
2. helps the initiator tRNA bind properly
3. Prevents the large subunit from binding
   L> normally a tRNA with a fresh aa goes to site a but fMET (in bacteria this is where AU is located..) it goes to the P site.
   L> this only happens once…every tRNA comes in and goes to A site with a fresh aa this point onward…only fMet foes to Psite.

Question 17

Elongation of Polypeptide:
- Requires
L> ____ to bind to ribosome
L> ____ formation via peptidyl transferase
L> ____ exactly one codon toward the 3’ end of mRNA.

Answer 17

• Amnioacyl tRNA
• Peptide bond
• Ribosome translocates

Question 18

Nontranslated region is what?

Answer 18

everything to the left of the start codon!

L> aka upstream

Question 19

Polyribosome:

- After ribosome translocation occurs what happens?

Answer 19

• a second initiation of translation occurs…
  L> 8-1- ribosomes may synthesize proteins from a single mRNA molecule.
  L> if there is enough room on the mature RNA
  L> this happens in both eukaryotes and pros

Question 20

What is unique about translation in prokaryotes?

Answer 20

sometimes the 3’ end is still being transcribed while it is being translated….since mRNA is not processed beforehand like it is in eukaryotes.

Question 21

Termination of Translation?

- A chain terminating ____

Answer 21

• codon

Question 22

Termination of Translation?

- The cain terminating codon is recognized by ?

Answer 22

• release factors
  L> release of polypeptide in P site from tRNA
  L> release empty tRNA from ribosome
  L> release ribosomal subunits from mRNA
  L> once the tRNA is empty it will go to get charged again to be used.