Question 1

Which of the following best describes the structure of DNA as depicted in the first image?

Accepted Answer

A double helix with antiparallel strands held together by hydrogen bonds between complementary bases

Question 2

In the semi-conservative replication model (second image), what is the composition of each daughter DNA molecule after one round of replication?

Accepted Answer

Each contains one parental and one newly synthesized strand

Question 3

A bacterial cell is exposed to a chemical agent, as shown in the third image (Ames test plate). What does the high number of colonies around the disk indicate?

Accepted Answer

The agent induces mutations, increasing the reversion rate

Question 4

The fourth image shows two bacterial cells connected by a pilus. What process is being illustrated?

Accepted Answer

Conjugation

Question 5

Which enzyme is responsible for unwinding the DNA double helix during replication?

Accepted Answer

Helicase

Question 6

What is the main difference between the leading and lagging strands during DNA replication?

Accepted Answer

The leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized discontinuously away from the fork in Okazaki fragments

Question 7

Which of the following best describes a plasmid?

Accepted Answer

A circular, self-replicating, extrachromosomal DNA molecule found in prokaryotes

Question 8

Which type of mutation is most likely to result in a nonfunctional protein due to a shift in the reading frame?

Accepted Answer

Frameshift mutation

Question 9

What is the function of DNA ligase during DNA replication?

Accepted Answer

It joins Okazaki fragments by sealing nicks in the sugar-phosphate backbone

Question 10

Which of the following statements about the lac operon is correct?

Accepted Answer

It is an inducible operon that is turned on only when lactose is present and glucose is low

Question 11

Which of the following best describes the role of an R plasmid?

Accepted Answer

It confers resistance to antibiotics or heavy metals

Question 12

Which of the following is a property of RNA polymerase that distinguishes it from DNA polymerase?

Accepted Answer

It can start RNA synthesis de novo without a primer

Question 13

Which of the following is true regarding generalized transduction?

Accepted Answer

Random fragments of bacterial DNA are packaged into phage particles and transferred to a new host

Question 14

Which of the following best describes an auxotroph?

Accepted Answer

A mutant organism that cannot synthesize a specific nutrient and must obtain it from the environment

Question 15

Which of the following is a function of DNA methylation in bacteria?

Accepted Answer

It can regulate gene expression and control initiation of DNA replication

Question 16

Which of the following is a key difference between prokaryotic and eukaryotic protein synthesis?

Accepted Answer

Prokaryotes couple transcription and translation in the cytosol, while eukaryotes separate these processes

Question 17

Which of the following best describes the effect of ionizing radiation on DNA?

Accepted Answer

It causes breaks in the sugar-phosphate backbone, leading to large deletions

Question 18

Which of the following is an example of a base analog mutagen and its effect?

Accepted Answer

5-bromouracil; can replace thymine and pair with guanine, causing base-pair substitutions

Question 19

Which of the following statements about the Ames test is correct?

Accepted Answer

It screens chemicals for mutagenic potential using Salmonella that cannot synthesize histidine

Question 20

Which of the following is true about conjugation in bacteria?

Accepted Answer

It involves direct cell-to-cell contact and transfer of plasmid DNA via a pilus

Microbial Genetics: Structure, Replication, Mutation, and Horizontal Gene Transfer

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