Mechanisms Of Prtein Synthesis

Question 1

What ribosomes are present in prokaryotic and eukaryotic cells

Answer 1

Prokaryotic- 70S (small, 30S subunits and large,50S subunits)
Eukaryotic- 80S (40S and 60S Subunits)

Question 2

What sites to ribosomes have

Answer 2

3 tRNA binding sites
1. E SITE- exit site
2. P site- peptidyl sites
3. A site- acceptor site

Question 3

What is the role of tRNA

Answer 3

tRNA forms a complex with a specific AA - ‘aminoacyl -tRNA’

Anticodon is the template recognition site

AminoacylTion of tRNA = AA attachment to corresponding tRNA molecules “loading”

AA is esterified to the 3’ hydroxyl group of the final adenosine of tRNA

Question 4

What are aminoacyl- tRNA syntehtase

Answer 4

• enzymes that attach AA to tRNA molecules
  -Highly specific for each AA
• can differentiate between AA with similar structure
• have proofreading function to hydrolyse wrongly charged tRNAs

Question 5

Name some elongation factors

Answer 5

EF-Ty are proteins that deliver aminoacyl-tRNA to the ribosome in the cytosol

Question 6

What is the wobble hypothesis

Answer 6

TRNA molecules can recognise more than one codon - enables redundancy in the genetic code as one tRNA recognises serval codons

Can also be several tRNA with same AA for different anticodons

Question 7

What is the inaition code for protein synthesis

Answer 7

AUG- methionine

Reading Frames are determined by the respective start codon and strength of ribosome binding site

Question 8

How are proteins synthesised

Answer 8

By successive addition of AA to the carboxyl terminus of the pp and peptide bond formation

Growing pp chain is extruded through a tunnel in the large subunit of the ribosome

Question 9

What is a polysone

Answer 9

“ cluster of ribosomes held together by a strand of mRNA which each is trnaslating”

Question 10

What are the triplet codons characteristics

Answer 10

1. Redundancy- 20 AA but 64 possible triplet codons that code for them
2. Unambiguity - each codon can only encode 1 specific AA or START/STOP
3. Universality- all living organism have same genetic code based on chemistry

Question 11

What is polycistronic and monicistrony

Answer 11

Prokaryotic mRNA is polycistronic and can only encode for more than one protein simultaneously
Has multiple bribing sites

Eukaryotic mRNA is monocistronic and binds to one ribosome and encodes one protein