Q: During the log (exponential) phase of bacterial growth, the number of cells at time $$t$$ can be calculated using which of the following equations?

$$N_t = N_0$ \times 2$$^{n}$$, where n$ is the number of generations$

Question 1

A researcher wants to estimate the number of viable bacteria in a water sample. Which method would be most appropriate for specifically counting only living cells, and why?

Accepted Answer

Spread-plate method, because only viable cells will form colonies on the agar.

Question 2

During the log (exponential) phase of bacterial growth, the number of cells at time $$t$$ can be calculated using which of the following equations?

Accepted Answer

$$N_t = N_0$ 	imes 2$$^{n}$$, where n$ is the number of generations$

Question 3

Which adaptation would you expect to find in the membrane lipids of a thermophilic bacterium?

Accepted Answer

Increased proportion of saturated fatty acids to enhance membrane stability at high temperatures.

Question 4

A bacterium is found to grow optimally at pH 3. Which of the following adaptations is most likely present in its proteins?

Accepted Answer

Altered amino acid composition to prevent denaturation in acidic environments.

Question 5

Which enzyme is responsible for removing supercoils ahead of the replication fork during DNA replication in bacteria?

Accepted Answer

DNA gyrase

Question 6

In the lac operon, what is the effect of high glucose and low lactose on transcription of the lac genes?

Accepted Answer

Transcription is repressed due to active repressor and low cAMP levels.

Question 7

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

Accepted Answer

Nonsense mutation

Question 8

Which of the following best describes the function of RecA protein in bacterial cells?

Accepted Answer

It facilitates homologous recombination and DNA repair.

Question 9

A bacterial cell is exposed to UV light, resulting in thymine dimers. Which DNA repair mechanism is most likely to be activated?

Accepted Answer

Excision repair

Question 10

Which of the following statements about generalized transduction is correct?

Accepted Answer

Any bacterial gene can be transferred by a lytic phage during assembly.

Question 11

A patient is infected with a strain of Staphylococcus aureus that expresses virulence factors only at high cell density. Which regulatory mechanism is most likely responsible?

Accepted Answer

Quorum sensing

Question 12

Which of the following best explains why influenza viruses can cause pandemics through antigenic shift?

Accepted Answer

Reassortment of genome segments from different viral strains infecting the same cell.

Question 13

Which of the following is a key feature of the lytic cycle of bacteriophage T4?

Accepted Answer

Modification of host RNA polymerase to preferentially transcribe phage genes.

Question 14

A bacterial strain is found to be resistant to high salt concentrations. Which adaptation is most likely responsible for this halophilic trait?

Accepted Answer

Accumulation of compatible solutes such as proline or glycine betaine.

Question 15

Which of the following statements about the F-plasmid in E. coli is correct?

Accepted Answer

Integration of the F-plasmid into the chromosome creates an Hfr strain capable of genome mapping.

Question 16

Which of the following best describes the function of alternate sigma factors in bacteria?

Accepted Answer

They allow RNA polymerase to recognize different sets of promoters under specific conditions.

Question 17

A compound transposon differs from a simple transposon in that it:

Accepted Answer

Is flanked by two insertion sequences and can carry additional genes such as antibiotic resistance.

Question 18

Which of the following is a unique feature of retroviruses such as HIV?

Accepted Answer

They use reverse transcriptase to synthesize DNA from an RNA template.

Question 19

In the context of gene evolution, which statement is correct regarding orthologous and paralogous genes?

Accepted Answer

Orthologous genes are homologous genes in different species that evolved from a common ancestral gene.

Question 20

A scientist is studying a virus with a +RNA genome that, upon infection, is directly translated by host ribosomes. Which virus is most likely being studied?

Accepted Answer

Poliovirus

Microbial Growth, Molecular Biology, Gene Regulation, Mutation, and Viral Diversity: Study Guide for Biology 331 Exam 2

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