23: W2 An RNA machine for protein synthesis: the ribosome

Question 1

Describe the large subunit of the bacterial (prokaryotic ) ribosome

Answer 1

(50s)

Question 2

Describe the small subunit of the bacterial (prokaryotic ) ribosome

Answer 2

(30S)

Question 3

Describe the large subunit of the human (eukaryotic) ribosome

Answer 3

(60S)

Question 4

Describe the small subunit of the human (eukaryotic) ribosome

Answer 4

(40S)

Question 5

What is the interface that the small and large ribosome subunit interact with each other?

Answer 5

The catalytic site

Question 6

What is the small subunit interface important for?

Answer 6

Decoding the mRNA being translated

Question 7

What is the large subunit interface important for?

Answer 7

Important for the peptidyl transferase activity (catalysis of protein synthesis)

Question 8

Describe the role of the tRNA

Answer 8

The molecular adaptor

-In order for high fidelity, the right tRNA must enter the ribosome, the pairing between the codon and the tRNA anti-codon must be accurate and the correct amino acid must be attached to the tRNA

Question 9

Describe the structure of the tRNA

Answer 9

• Much of the tRNA structure is dispensable (the nucleotides can be variable),
• the majority of conserved nucleotides are found in the loop regions. Many of the nucleotides are modified in order to give them structural specificity so that they can be recognised by the ribosome

Question 10

Describe aminoacyl tRNA synthetase

Answer 10

They are enzymes that attach the amino acids to the tRNAs

-Have specific structures that recognise the modified bases and the anticodon of the tRNA and can specifically recognise which amino acid to attach.

These enzymes can even remove the amino acid if the wrong one gets attached

Question 11

Describe cognate recognition

Answer 11

• First two base pairs are standard (A/U and G/C)
• Third position (wobble position) there is some leniency e.g. G/U pairing is accepted
• This is acceptable for recognition and the amino acid attached will be added to the growing polypeptide chain

Question 12

Describe near-cognate recognition

Answer 12

If positions 1 or 2 have G/U base pairing this will be rejected, as there is more importance put on the pairing at these positions on the codon

Question 13

Describe non-cognate recognition

Answer 13

When none of the positions can easily base pair

Question 14

What are the three fundamental activities of the ribosome

Answer 14

1. Decode the mRNA
2. Maintain fidelity of information transfer and read
   code successively in three letter groupings
3. Peptide bond formation

Question 15

Which part of the ribosome does antibiotics in this area target/?

Answer 15

Most antibiotics are effective because they bind to either the coding centre or the catalytic centre of the bacterial ribosome

Question 16

What occurs during Acute Aminoglycoside induced deafness (AAID)

Answer 16

• In the case of AAID (acute aminoglycoside induced deafness) there is a previously silent mutation in the gene for the mitochondrial ribosomal RNA (A to a G in the rRNA), which makes the patient’s ribosomes more sensitive to aminoglycosides and thereby inhibited just like the bacterial ribosomes. For many reasons not totally clear the hair cells in the ear are particularly sensitive (and as well, cells in the kidney).

• In the mitochondrial RNA this is an “A” -when it changes to a “G” (the mutation in AAID) then in makes humans susceptible to the horrendous side effects of the antibiotic.