Chapter 25 Self-test questions

. What would be the effect on the primary structure of the coded protein if a single base was deleted from a messenger RNA transcript?

No effect.

A single amino acid residue is changed.

A complete change in amino acid sequence from the point of the deletion.

A premature termination of the chain at the point of mutation.

. How many different transfer RNA molecules are present in a cell (not including those present in the mitochondria)?

64.

61.

20.

More than 20, less than 61.

. What is the correct constitution of a eukaryotic ribosome?

70S overall with a 50S and a 20S subunit.

70S overall with a 50S and a 30S subunit.

80S overall with a 60S and a 20S subunit.

80S overall with a 60S and a 40S subunit.

. Which of the following proteins involved in peptide initiation and chain elongation is a GTPase switch?

Only EF-Tu.

Only EF-G.

Both EF-Tu and EF-G.

Initiation factor 2.

. Which of the following enzymes involved in ribosomal protein synthesis is a ribozyme i.e. a catalytic RNA molecule?

Amino acyl t-RNA synthetase.

Peptidyl transferase.

Release factors 1 and 2.

Ribosome recycling factor.

. The major differences between the prokaryotic and eukaryotic protein synthesis mechanisms are in which part of the process?

The initiation of synthesis.

The chain elongation process.

The chain termination process.

None–there are no major differences.

. What is the role of chaperone proteins in protein synthesis?

Assisting correct folding of the newly formed polypeptide chain.

Correct formation of disulphide bridges in protein folding.

Release of completed proteins from the ribosome.

Switching peptide bonds that involve proline residues between the cis and the trans configurations.

. Which statement regarding ubiquitin is correct?

Ubiquitin is a carbohydrate group that marks proteins for destruction in proteasomes.

Ubiquitin is a short peptide sequence that marks proteins for destruction in proteasomes.

Ubiquitin is attached to proteins by the enzyme peptidyl transferase.

Ubiquitin is found in both prokaryotes and eukaryotes.

. The assignment of codons to amino acids in the genetic code is totally random and accidental. True or false?

True.

False.

. The three base anticodon of some transfer RNAs can contain a base other than the A, U, C, and G bases normally found in RNA. True or false?

True.

False.

. Which of the following mechanisms accounts for the addition of a new amino acid residue into a partially completed peptide chain on the ribosome?

The amino acid is transferred to link via its –NH₂ group to the C-terminal end of the peptide.

The peptide is transferred to link via its C-terminal end to the –NH₂ of the amino acid.

The amino acid is transferred to link via its –COOH group to the N-terminal end of the peptide

The peptide is transferred to link via its N-terminal end to the –COOH of the amino acid.

. Which of the following is required to ensure incorporation of the correct amino acid residue into a protein?

Very high specificity of amino acyl t-RNA synthetase for t-RNA and amino acid.

A proofreading mechanism within all amino acyl t-RNA synthetases to remove any incorrectly attached amino acids.

A mechanism to hydrolyse any amino acyl t-RNAs with the incorrect amino acid attached.

Absolute specificity between the m-RNA codon and the t-RNA anticodon.

. How is the prokaryotic ribosome positioned on the messenger RNA strand in the correct place to initiate translation?

It binds to free 5' end of the m-RNA.

It recognises and binds the start message codon AUG.

Ribosomal proteins recognise and bind a base sequence just upstream from the message start point.

Ribosomal RNA base pairs with a base sequence just upstream from the message start point.

. During prokaryotic protein synthesis amino acyl t-RNAs are all delivered to the ribosome by the cytoplasmic protein EF-Tu.

True.

False.

. How many ribosomes would you expect to be attached to a length of messenger RNA coding for a protein 180 amino acid residues long? Select the most likely answer.

1.

2.

10.

5.

. What is the role of Hsp60 (GroEL/GroES) in protein folding?

To direct the three-dimensional folding of a protein.

To hold a peptide in extended form until its synthesis is complete and correct folding can occur.

To provide a sequestered chamber where protein folding can occur without interference from surrounding molecules.

To 'rescue' denatured or incorrectly folded protein giving it a chance to refold.

. Proteasomes destroy proteins by unfolding them and chopping them into small fragments. What kinds of proteins are recognised by proteasomes?

Proteasomes recognise ubiquitinylated proteins.

Proteasomes recognise denatured proteins.

Proteasomes recognise proteins with basic or aromatic amino acids at the N-terminus.

Proteasomes recognise viral proteins.

Chapter 25 Self-test questions

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