Question 1

Which of the following best describes the role of EF-Tu during bacterial translation elongation?

Accepted Answer

It delivers aminoacyl-tRNA to the A site of the ribosome in a GTP-dependent manner.

Question 2

A mutation changes a codon from UAU (tyrosine) to UAA (stop codon). What type of mutation is this, and what is a likely consequence?

Accepted Answer

Nonsense mutation; translation will terminate prematurely, producing a truncated protein.

Question 3

Which of the following statements about the resting membrane potential in neurons is correct?

Accepted Answer

It is approximately $$-60\ \mathrm{mV} in $$the squid giant axon and is maintained by the Na$$^+/K$^+$$ pump and potassium leak channels.

Question 4

Which of the following best explains why the myelin sheath increases the speed of nerve impulse conduction?

Accepted Answer

It insulates the axon, forcing action potentials to jump between nodes of Ranvier (saltatory conduction).

Question 5

A patient is diagnosed with sickle-cell anemia, which is caused by a single base-pair substitution in the hemoglobin gene. What is the molecular consequence of this mutation?

Accepted Answer

A missense mutation that replaces glutamic acid with valine in the protein.

Question 6

Which of the following is true regarding the catalytic activity responsible for peptide bond formation during bacterial translation?

Accepted Answer

It is catalyzed by the 23S rRNA, making the ribosome a ribozyme.

Question 7

Which of the following best describes a frameshift mutation?

Accepted Answer

A mutation caused by insertions or deletions (indels) that alter the reading frame of the gene.

Question 8

During translation termination in bacteria, what is the role of release factors?

Accepted Answer

They recognize stop codons at the A site and trigger release of the polypeptide from the tRNA.

Question 9

Which of the following is a real-life example of a silent (synonymous) mutation?

Accepted Answer

A mutation that changes the codon GAA to GAG, both of which code for glutamic acid.

Question 10

Which of the following best describes the fate of an mRNA in eukaryotic cells that contains a premature stop codon upstream of the final exon junction complex (EJC)?

Accepted Answer

It is targeted for degradation by nonsense-mediated decay.

Question 11

Which of the following is a function of glial cells in the nervous system?

Accepted Answer

They form the myelin sheath around axons and help maintain the blood-brain barrier.

Question 12

Which of the following best explains why the Na$$^+/K$^+$$ pump is essential for maintaining the resting membrane potential?

Accepted Answer

It actively transports three sodium ions out and two potassium ions into the cell, maintaining ionic gradients.

Question 13

A bacterial mRNA lacks a stop codon due to a mutation. What is the most likely cellular response?

Accepted Answer

A transfer messenger RNA (tmRNA) will bind the A site, allowing translation to terminate and tagging the defective protein for degradation.

Question 14

Which of the following is true about the specificity of voltage-gated ion channels in neurons?

Accepted Answer

It is determined by the size and charge of the central pore and the arrangement of oxygen atoms in the channel.

Question 15

Which of the following best describes the process of channel inactivation in voltage-gated ion channels?

Accepted Answer

A part of the channel called the inactivating particle blocks the pore, preventing ion flow even if the membrane is depolarized.

Question 16

Which of the following posttranslational modifications occurs in both bacteria and eukaryotes?

Accepted Answer

Removal of the methionine at the N-terminus.

Question 17

Which of the following scenarios would most likely result in a nonstop mutation?

Accepted Answer

A base-pair substitution changes a stop codon to a sense codon, allowing translation to continue beyond the normal stop site.

Question 18

Which of the following best describes the function of synaptic boutons in motor neurons?

Accepted Answer

They transmit signals to the next cell, such as a neuron, muscle, or gland, via neurotransmitter release.

Question 19

Which of the following is a direct consequence of opening voltage-gated sodium channels during an action potential?

Accepted Answer

Sodium ions enter the neuron, causing depolarization of the membrane.

Translation Mechanisms, Mutations, and Neuronal Signaling: Structured Study Notes for Cell Biology

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