Protein Synthesis

Question 1

What is the central dogma?

Answer 1

Generalised flow of information

Question 2

How many possible codons are there and how many stop codons?

Answer 2

64 codons and 3 stop codons

Question 3

What does synonymous mutations (silent variations) mean?

Answer 3

The variation within codons

Question 4

Where are the two populations of ribosome found?

Answer 4

Bound to the ER and free within the cytoplasm

Question 5

How fast is protein synthesis (how many aa’s per second)?

Answer 5

20 aa’s per second

Question 6

What is mammalian ribosomes made of and how many rRNA and protein molecules are there?

Answer 6

2 units:
40s- 18s rRNA and 33 proteins
60s- 3 rRNA and 49 proteins

Question 7

How many binding sites are there inside the ribosome and what are they called?

Answer 7

3:
Aminoacyl tRNA binding site (the A site)
Peptidyl binding site (the P site)
Exit ( the E site)

Question 8

What are the 3 stages in protein synthesis and a brief overview of each stage?

Answer 8

Initiation: ribosome assembles with the first initiator tRNA
Elongation: charged tRNAs delivered to the ribosome and aa’s are added one at a time
Termination: reach the stop codon and ends protein synthesis with the release of the polypeptide

Question 9

How are initiation factors named?

Answer 9

Eif and a number

Question 10

How are elongation factors named?

Answer 10

Ef and a number

Question 11

How are proteins that aren’t initiation or elongation factors named?

Answer 11

L or S for large or small subunits and a number

Question 12

Give the steps in the initiation stage of protein synthesis

Answer 12

• eif4 and 5 bind to the cap and poly A binding protein binds to the poly A tail
• eif2 and GTP binds to met-tRNA which attaches to the P binding site forms the 48s pro-initiation factor
• scanning process starts (to find the start codon)
• when the start codon is found the 80s ribosome is formed and eif2 and other factors are released
• 2nd aminoacyl tRNA enters the A site with the elongation factor 1

Question 13

How much energy is used in the translation of a single triplet codon

Answer 13

One molecule of ATP

Question 14

Give the steps of the elongation stage of protein synthesis

Answer 14

• aa + ATP+ tRNA-> aminoacyl tRNA + AMP+2Pi
• aminoacyl tRNA binds to the A site and GTP is hydrolysed
• peptidyl transferase then attaches the chain to the new aa
• EF2 then allows for the translocation fo the ribosome along the chain
• tRNA then recharges using GTP

Question 15

What is a polysome?

Answer 15

When one message makes many proteins

Question 16

Describe the steps in the termination stage of protein synthesis

Answer 16

• when the ribosome gets to a stop codon, it brings a release factor
• then the terminal peptidyl-tRNA is hydrolysed and the chain is released
• the ribosome then dissociates and its recycled into the cell

Question 17

How much energy does charging tRNAs with amino acids use?

Answer 17

1ATP/aa

Question 18

What energy does the initiation of polypeptide synthesis use?

Answer 18

GTP +nATP

Question 19

How much energy does elongation use?

Answer 19

2GTP/AA

Question 20

How much energy does the termination of polypeptide synthesis use?

Answer 20

GTP

Question 21

Which part of the ribosome does streptomycin target?

Answer 21

Small ribosomal subunit

Question 22

Which part of the ribosome do tetracyclines target?

Answer 22

Small ribosomal subunit