Question 1

Which of the following best describes the difference between the leading and lagging strands during DNA replication?

Accepted Answer

The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized discontinuously as Okazaki fragments in the 5' to 3' direction.

Question 2

A mutation changes the codon GAG (which codes for glutamic acid) to GUG (which codes for valine). What type of mutation is this, and what is a possible consequence?

Accepted Answer

Missense mutation; it may alter the protein's function by substituting one amino acid for another.

Question 3

Which enzyme is responsible for joining Okazaki fragments during DNA replication?

Accepted Answer

DNA ligase

Question 4

During bacterial conjugation, which structure is essential for the transfer of genetic material between cells?

Accepted Answer

Pilus

Question 5

Which of the following best explains why retroviruses require the enzyme reverse transcriptase?

Accepted Answer

To synthesize DNA from their RNA genome, allowing integration into the host genome.

Question 6

A patient is infected with a Gram-negative bacterium that produces endotoxin. Which of the following statements about endotoxins is correct?

Accepted Answer

Endotoxins are lipopolysaccharides (LPS) found in the outer membrane of Gram-negative bacteria and are less potent than exotoxins.

Question 7

Which of the following is a correct sequence of events in the lytic replication cycle of a bacteriophage?

Accepted Answer

Attachment → Penetration → Biosynthesis → Maturation → Release

Question 8

If Pathogen A has an $$LD_{50} of 100 $$and Pathogen B has an $$LD_{50} of 10$$,000, which is more virulent and why?

Accepted Answer

Pathogen A is more virulent because a lower $$LD_{50}$$ means less pathogen is needed to cause death in 50% of hosts.

Question 9

Which of the following best describes the function of an operon in prokaryotic cells?

Accepted Answer

It coordinates the expression of multiple related genes under the control of a single promoter.

Question 10

A bacterial cell acquires antibiotic resistance through horizontal gene transfer via transduction. Which agent is responsible for this transfer?

Accepted Answer

Bacteriophage (virus)

Question 11

Which of the following is a key difference between the lysogenic and lytic cycles of bacteriophage replication?

Accepted Answer

The lysogenic cycle involves integration of phage DNA into the host genome as a prophage, while the lytic cycle results in immediate host cell lysis.

Question 12

Which of the following best explains how bacterial capsules contribute to pathogenicity?

Accepted Answer

Capsules inhibit phagocytosis by host immune cells, allowing bacteria to evade immune responses.

Question 13

During translation, which molecule brings the correct amino acid to the ribosome by matching its anticodon to the mRNA codon?

Accepted Answer

tRNA

Question 14

Which of the following is a characteristic of exotoxins?

Accepted Answer

They are proteins, often highly potent, and usually secreted by Gram-positive bacteria.

Question 15

A scientist is studying a virus with a single-stranded RNA genome that must be reverse transcribed into DNA before integration into the host genome. Which type of virus is this?

Accepted Answer

Retrovirus

Question 16

Which of the following best describes the role of fimbriae (adhesins) in bacterial pathogenesis?

Accepted Answer

They facilitate attachment of bacteria to host cell surfaces.

Question 17

Which of the following is a correct match between a mutation type and its effect?

Accepted Answer

Nonsense mutation: introduces a premature stop codon, truncating the protein.

Question 18

Which of the following best explains why RNA viruses generally have higher mutation rates than DNA viruses?

Accepted Answer

RNA-dependent RNA polymerases lack proofreading activity, leading to more errors during replication.

Question 19

Which of the following is a correct order of steps in the central dogma of molecular biology?

Accepted Answer

DNA $$\rightarrow$$ RNA $$\rightarrow$$ Protein

Question 20

A patient is infected with a virus that causes the formation of syncytia (multinucleated giant cells) in host tissues. What is the most likely effect of this cytopathic change?

Accepted Answer

It allows the virus to spread directly from cell to cell, evading immune detection.

Microbiology Study Guide: DNA Replication, Viruses, and Pathogenicity Mechanisms

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