Question 1

Which of the following statements best describes the difference between genotype and phenotype in a bacterial cell?

Accepted Answer

Genotype is the entire genetic material of an organism, while phenotype is the expressed properties resulting from gene expression.

Question 2

During DNA replication in E. coli, which enzyme is responsible for joining Okazaki fragments on the lagging strand?

Accepted Answer

DNA ligase

Question 3

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

Accepted Answer

Nonsense mutation; introduces a stop codon and likely truncates the protein

Question 4

Which of the following best explains why the genetic code is described as 'degenerate'?

Accepted Answer

Multiple codons can code for the same amino acid.

Question 5

In the lac operon, what is the role of allolactose?

Accepted Answer

It acts as an inducer by inactivating the repressor, allowing transcription.

Question 6

Which of the following is a correct sequence of events in the central dogma of molecular biology?

Accepted Answer

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

Question 7

A bacterium is exposed to ultraviolet light, resulting in the formation of thymine dimers. Which repair mechanism uses visible light to directly reverse this damage?

Accepted Answer

Photoreactivation (light repair) using photolyase

Question 8

Which of the following best describes a frameshift mutation?

Accepted Answer

One or more nucleotides are inserted or deleted, altering the reading frame.

Question 9

In the trp operon, what happens when tryptophan is abundant in the environment?

Accepted Answer

Tryptophan acts as a co-repressor, activating the repressor to turn the operon off.

Question 10

Which of the following is true about plasmids?

Accepted Answer

They are self-replicating, extrachromosomal DNA molecules that may carry antibiotic resistance genes.

Question 11

A scientist wants to select for E. coli mutants that are resistant to ampicillin. Which method should she use?

Accepted Answer

Positive selection by growing cells on ampicillin-containing medium

Question 12

Which of the following statements about bacterial conjugation is correct?

Accepted Answer

It involves direct cell-to-cell contact and transfer of plasmid DNA.

Question 13

Which enzyme is responsible for relaxing supercoils ahead of the replication fork during DNA replication?

Accepted Answer

DNA gyrase

Question 14

A bacterial cell is able to take up naked DNA from its environment and incorporate it into its genome. This process is called:

Accepted Answer

Transformation

Question 15

Which of the following best describes the function of transposons?

Accepted Answer

They are segments of DNA that can move from one location to another within a genome.

Question 16

In a scenario where both glucose and lactose are present in the growth medium, which sugar will E. coli preferentially use and why?

Accepted Answer

Glucose, because catabolite repression ensures glucose is used first.

Question 17

Which of the following is a real-world example of horizontal gene transfer in bacteria?

Accepted Answer

A bacterium acquiring antibiotic resistance genes from another bacterium via conjugation.

Question 18

Which of the following best explains why silent mutations often do not affect the phenotype of an organism?

Accepted Answer

They result in a codon that codes for the same amino acid due to the degeneracy of the genetic code.

Question 19

Which of the following is NOT a function of tRNA during translation?

Accepted Answer

Forming peptide bonds between amino acids

Question 20

A bacteriophage accidentally packages host bacterial DNA and transfers it to another bacterium. This process is known as:

Accepted Answer

Transduction

Microbial Genetics: Structure and Function of Genetic Material

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