Translation

Question 1

Triplet codon

Answer 1

1 triplet codon or 3 bases codes for 1 amino acid.

Note it is in RNA code so UGAC

Question 2

Translation involving mRNA structure

Answer 2

In 5' to 3' direction
Ribosomal binding site
Start codon
Coding sequence
Stop codon

Question 3

Ribosomal binding site

Answer 3

Site for ribosome binding

Question 4

Start codon

Answer 4

A codon that specifies the first amino acid in a polypeptide sequence to be translated

Question 5

Coding sequence

Answer 5

A series of codons from start codon to stop codon that determine amino acid sequence of a polypeptide.

Question 6

Stop codon

Answer 6

Specifies the end of translation

Question 7

List the 5 components for translation

Answer 7

Ribosome
mRNA
Charged tRNA
Initiation and elongation factors
Energy from hydrolysis of GTP

Question 8

Ribosomes

Answer 8

Site of protein synthesis
Consists of rRNA and proteins
Arranged as 2 subunits

Question 9

List the 2 subunits that make up the ribosomes

Answer 9

Small subunit - associates with mRNA

Large subunit - associates with charged tRNA

Question 10

List the 2 important tRNA binding sites in a large subunit

Answer 10

Contains 3 important tRNA binding sites

1) P site
2) A site
3) Exit site

Question 11

P site function

Answer 11

During protein translation, the P-site holds the tRNA which is linked to the growing polypeptide chain

Question 12

A site function

Answer 12

The A site accepts an incoming tRNA bound to an amino acid.

Question 13

Ribosome large subunit contains peptidyl transferase enzyme

Answer 13

it catalyzes the addition of an amino acid residue in order to grow the polypeptide chain in protein synthesis

Question 14

Ribosomal subunits and rRNA naming after their S value

Answer 14

Named using parameters called S value or swedburg value.

S value refers to sedimentation value

Question 15

Larger ribosomal subunits vs smaller ribosomal subunits

Answer 15

Larger ribosomal subunits sediment quicker than smaller ribosomal subunits.

Question 16

tRNA function

Answer 16

Adapts each mRNA triplet codon to tis correct amino acid

Question 17

2 characteristics of tRNA

Answer 17

• Short, composed of 75 to 90 nucleotides

- Single stranded RNA, folds on itself to form secondary structure

Question 18

List 2 structures and their functions of tRNA

Answer 18

1) Anti-codon loop
Each tRNA contains 3 unpaired bases (triplet anticodon) at the center of the middle loop which can base pair with the complementary mRNA triplet codon.

2) tRNA 3’ acceptor region
Covalently binds to a specific amino acid and brings it to mRNA at ribosome

Question 19

What is required by tRNA 3’ acceptor region to bind free amino acid

Answer 19

Aminoacyl tRNA synthetase and ATP are required to covalently bind free amino acid to the 3’ acceptor region of tRNA.

Question 20

List the 3 Protein factors of Initiation of translation

Answer 20

IF1, IF2, IF3

Question 21

IF1 function

Answer 21

Stabilize 30S subunit

Question 22

IF2 function

Answer 22

Binds tRNA fmet to 30S-mRNA: binds to GTP and stimulate hydrolysis

Question 23

IF3 function

Answer 23

Binds 30S subunit to mRNA, dissociate monomers to subunit at termination

Question 24

List the 3 Protein factors of elongation of polypeptides

Answer 24

EF-Tu, EF-Ts, EF-G

Question 25

EF-Tu

Answer 25

Binds GTP, brings aminoacyl-tRNA to the site of ribosome

Question 26

EF-Ts

Answer 26

Generates active EF-Tu

Question 27

EF-G

Answer 27

Stimulates translocation, GTP-dependent

Question 28

List the 3 protein factors to cause the termination of transcription and release of polypeptide

Answer 28

RF-1, RF-2, RF-3

Question 29

RF-1

Answer 29

Catalyzes release of polypeptide chain from tRNA and dissociation of translocation complex; specific for UAA & UAG termination codons

Question 30

RF-2

Answer 30

Behaves like RF-1; specific for UGA and UAA

Question 31

RF-3

Answer 31

F-3 Stimulates RF-1 & RF-2

Question 32

Initiation step

Answer 32

1. Small ribosomal subunit binds to a specific sequence on the mRNA 2. A specific tRNA with the complementary anticodon (UAC), binds to the start codon (AUG) on the mRNA 3. This tRNA which functions as the initiator tRNA, carries a modified form of methionine called N-formylmethionine (fMet) 4. Large ribosomal unit then binds to ribosome small unit + mRNA

Question 33

Shine dalgarno sequence

Answer 33

Shine-Dalgarno (SD) sequence (prokaryotes) * AGGAGG consensus sequence located before mRNA start codon (AUG) * Associate with 16S rRNA of small ribosome subunit

Question 34

List the 3 steps In prokaryotes regarding fMet

Answer 34

- > The first amino acid inserted into all proteins is a modified form of methionine called N-formylmethionine (fMet) using tRNAf Met - > When translation is completed, the formyl group or the entire fMet residue is removed - > Normal methionine (Met) is added when AUG appears internally (using tRNAm Met)

Question 35

fMet in bacteria

Answer 35

H Formyl group I C = O I NH O II II CH3 - S - CH2 - CH2 - C - C - O I H

Question 36

List the 6 steps in Elongation in prokaryotes

Answer 36

1. First charged tRNA is tRNAf Met which occupies the P site of ribosome and base-pairs with AUG (CODON 1) of mRNA. 2. Second charged tRNA is attracted to the second mRNA codon (CODON 2) by complementary base-pairing and occupies the A site of the ribosome. 3. Once both P site and A site are filled with charged tRNAs, peptidyl transferase catalyzes the formation of a peptide bond between the two amino acids. 4. Concurrently, the covalent (ester) bond between the amino acid and the tRNA occupying the P site is hydrolysed, and the uncharged tRNA is released from the P site. 5. Dipeptide is formed, which is attached to the tRNA at the A site. 6. Elongation proceeds as ribosomes moves down 1 codon (5’ to 3’ direction).

Question 37

List the 3 steps Termination in prokaryotes

Answer 37

1. Ribosomes translate mRNA until it reaches a stop codon (UAG, UAA, UGA). 2. When a stop codon occupies the A site of the ribosome, it will be recognized by the ribosome and the finished polypeptide (at P site) is then cleaved from the terminal tRNA. 3. Polypeptide is released from the translation complex and the ribosome dissociates into large and small subunits

Question 38

List 9 difference in translation between prokaryotes and eukaryotes

Answer 38

- > Ribosomes are larger and protein components are more complex. - > mRNAs are much longer lived – most exist for hours (rather than minutes as in prokaryotes). - > mRNA is processed to have a 5’ 7mG cap and 3’ poly-A tail and splicing of introns. - > The 7mG cap is important for translation, mRNAs without 5’ cap are translated poorly. - > Instead of the Shine-Delgarno sequence, there is a Kozak sequence GCCRCCAUGG (a consensus sequence, where R is a purine - A or G). - > The start codon AUG is located within the Kozak sequence. - > The Kozak sequence marks the initiation of translation, to facilitate the binding to the small subunit of ribosome to mRNA. - > There is no need for fMet at the start codon (AUG).