Question 1

Which experiment provided the first direct evidence that DNA is the genetic material, and what was the key finding?

Accepted Answer

Avery, MacLeod, and McCarty's experiment; they showed that only DNA from S strain could transform R strain into S strain.

Question 2

In the Hershey-Chase experiment, what was the significance of using $$^{32}P$$ and $$^{35}S$$ isotopes?

Accepted Answer

$$^{32}P$$ labeled DNA and $$^{35}S$$ labeled protein, allowing them to track which molecule entered the bacterial cell.

Question 3

Which of the following best describes bacterial transformation?

Accepted Answer

Uptake of naked DNA from the environment by a competent cell and its incorporation into the genome.

Question 4

In the classic Griffith experiment, what was the outcome when mice were injected with a mixture of heat-killed S strain and live R strain of Streptococcus pneumoniae?

Accepted Answer

The mice died, and live S strain was recovered from their blood.

Question 5

Which enzyme treatment destroyed the transforming activity in the Avery, MacLeod, and McCarty experiment, proving the identity of the transforming principle?

Accepted Answer

DNase

Question 6

What is the role of RecA protein in bacterial transformation?

Accepted Answer

It mediates homologous recombination between incoming DNA and the host genome.

Question 7

Which of the following is a key feature of a plasmid used as a cloning vector?

Accepted Answer

It must contain an origin of replication and selectable marker genes.

Question 8

What is the main difference between generalized and specialized transduction?

Accepted Answer

Generalized transduction can transfer any part of the bacterial genome, while specialized transduction transfers only genes adjacent to the prophage integration site.

Question 9

In the context of horizontal gene transfer, what is a merozygote?

Accepted Answer

A bacterial cell that is partially diploid due to the presence of exogenote DNA.

Question 10

Which of the following best explains why the addition of excess non-transforming DNA can inhibit transformation efficiency?

Accepted Answer

The excess DNA saturates the DNA-binding receptors on the cell surface, preventing uptake of transforming DNA.

Question 11

Which of the following is NOT a step in the process of bacterial transformation with a plasmid?

Accepted Answer

Integration of the plasmid into the host chromosome is required for expression.

Question 12

What is the function of restriction endonucleases in molecular cloning?

Accepted Answer

They cleave DNA at specific recognition sequences, generating fragments for cloning.

Question 13

Which of the following statements about the pUC19 plasmid is correct?

Accepted Answer

It contains a multiple cloning site (MCS) for insertion of foreign DNA.

Question 14

In the interrupted mating experiment with Hfr and F- E. coli strains, what does the time of entry of a gene into the recipient cell indicate?

Accepted Answer

The genetic distance from the origin of transfer on the chromosome.

Question 15

Which of the following is a direct result of F' (F-prime) conjugation?

Accepted Answer

The recipient cell becomes partially diploid for certain genes.

Question 16

Which of the following best describes the role of DNA ligase in recombinant DNA technology?

Accepted Answer

It covalently joins DNA fragments with compatible ends.

Question 17

Why did the Hershey-Chase experiment use a blender in their protocol?

Accepted Answer

To separate phage protein coats from bacterial cells after infection.

Question 18

Which of the following is a common misconception about the Avery, MacLeod, and McCarty experiment?

Accepted Answer

That trace amounts of protein co-purifying with DNA were responsible for transformation.

Question 19

What is the main advantage of using multiple auxotrophic markers in bacterial genetic crosses?

Accepted Answer

It reduces the likelihood that observed prototrophy is due to reversion rather than recombination.

Horizontal Gene Transfer: Transformation, Conjugation, and the Discovery of DNA as Genetic Material

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