Chapter 7.3

Question 1

What are the three sites of the ribosome for tRNA

Answer 1

-the A site(aminoacyl), the P site(peptidyl) and the E site(exit

Question 2

Compare prokaryote ribosome size to that of eukaryote ribosome size

Answer 2

Prokaryotes
->have a 50S subunit and a 30S subunit to make a 70S ribosome

Eukaryotes
->have a 60S subunit and a 40S subunit to make a 80 S subunit

Question 3

What is the difference in translation between prokaryotes and eukaryotes

Answer 3

Prokaryotes
->translation begins before transcription even ends

Eukaryotes
->translation and transcription occur at separate times

Question 4

Describe the differences in initiation between prkaryotes and eukaryotes

Answer 4

Prokaryotes

• > small subunit binds to Shine-Dalgarno sequence in the 5’ untranslated region of the mRNA
• > charged initiator tRNA binds to the AUG start codon within the P site
• > the initial amino acid is fMet
• > then the large subunit binds to the small subunit and forms the initiation complex

Eukraryotes

• > small subunit binds to the 5’ cap structure
• > charged initiator tRNA binds to the AUG start codon within the P site
• > the initial amino acid is Met
• > then the large subunit binds to the small subunit and forms the initiation complex

Question 5

What are the roles of the initiation factors

Answer 5

• they help the large ribosomal subunit bind to the small one
• > they are not permanently associated with the ribosome

Question 6

Describe the general movement of mRNA during elongation

Answer 6

• it moves from the 5’ to the 3’ direction
• > along the mRNA
• > synthesizes from the N(amino) terminus to the C(carboxyl) terminus

Question 7

What are the functions of the A site, P site and the E site

Answer 7

A site

• > holds the incoming aminoacyl-tRNA complex
• > this is the next amino acid chain that is being added to the growing chain

P site

• > holds the tRNA that carries the growing polypeptide chain
• > peptide bond is formed as the polypeptide is passed from the tRNA in the P site to the tRNA in the A site
• > peptide bond formation is done by PEPTIDYL TRANSFERASE

E site

• > where the inactivated and uncharged tRNA pauses
• > uncharged tRNA releases the mRNA from the ribosome

Question 8

What is the role of peptidyl transferase? How does it achieve this role?

Answer 8

• its role is to form peptide bonds

- >it achieves this role by using GTP to form these bonds

Question 9

What is the function of elongation factors?

Answer 9

• they help to locate
• > and recruit aminoacyl-tRNA along with GTP
• > they also remove GDP once the energy has been used

Question 10

Describe the process of termination

Answer 10

• a stop codon moves into the A site
• a protein called the release factor binds to the termination codon
• > causing a water molecule to be added to the polypeptide chain
• addition of water to the chain= hydrolyzation of the completed polypeptide chain from the final tRNA
• > polypeptide chain dissociates from the P site
• > two ribosomal units then dissociate