Question 1

Which of the following best describes the main function of restriction enzymes in bacteria?

Accepted Answer

They recognize and cut specific DNA sequences as a defense mechanism against foreign DNA, such as that from bacteriophages.

Question 2

Why do bacterial restriction enzymes not cut the bacterium's own DNA?

Accepted Answer

The bacterial DNA is protected by the addition of methyl groups to specific bases within the recognition sites.

Question 3

During the process of RNA extraction using a spin column, what is the primary role of the chaotropic salts in the lysis buffer?

Accepted Answer

They disrupt proteins and inactivate RNases, aiding in the release and protection of RNA.

Question 4

In gene cloning, why is it important that the overhangs generated by restriction enzymes are complementary?

Accepted Answer

Complementary overhangs ensure that the DNA fragments can be ligated together efficiently by DNA ligase.

Question 5

A scientist is cloning a gene using restriction enzymes and a plasmid vector. Which of the following steps must occur immediately after the DNA fragments are cut with restriction enzymes?

Accepted Answer

The DNA fragments are ligated together using DNA ligase.

Question 6

Which of the following best explains why RNA binding to the silica membrane in a spin column typically occurs at acidic pH?

Accepted Answer

At acidic pH, the negative charges on the RNA backbone are neutralized, promoting binding to the silica.

Question 7

In the Meselson-Stahl experiment, which provided evidence for the semi-conservative model of DNA replication, what was the key observation after one round of replication in $$^{14}N$$ medium?

Accepted Answer

All DNA was of intermediate density between $$^{15}N$$ and $$^{14}N.$$

Question 8

A double-stranded DNA molecule consists of 30% cytosine (C). What is the percentage of adenine (A) in this molecule?

Accepted Answer

20%

Question 9

Two DNA molecules of equal length have different GC content: Molecule 1 has 40% GC, Molecule 2 has 60% GC. Which molecule will have a higher melting temperature ($$T_m) $$and why?

Accepted Answer

Molecule 2, because GC pairs form three hydrogen bonds, increasing thermal stability.

Question 10

Which of the following best describes the composition of eukaryotic ribosomes?

Accepted Answer

They are composed mostly of ribosomal RNA (rRNA) and ribosomal proteins, with rRNA forming the catalytic core.

Question 11

Where are eukaryotic ribosomes assembled?

Accepted Answer

In the nucleolus, where rRNA is transcribed and combined with ribosomal proteins.

Question 12

During DNA synthesis, which direction does DNA polymerase add nucleotides?

Accepted Answer

From the 5' to 3' direction, adding nucleotides to the 3' hydroxyl group.

Question 13

What is the driving force for the addition of nucleotides during DNA or RNA synthesis?

Accepted Answer

The hydrolysis of pyrophosphate ($$PP_i) $$released from the incoming nucleoside triphosphate.

Question 14

Why is ATP not specifically required for RNA synthesis, even though it is a nucleotide triphosphate?

Accepted Answer

RNA synthesis uses all four ribonucleoside triphosphates (ATP, GTP, CTP, UTP) as substrates, not just ATP.

Question 15

In a real-world scenario, a researcher is using a spin column to purify RNA from a tissue sample. After binding and washing steps, the researcher elutes the RNA with a low-salt buffer. What is the main reason for using a low-salt buffer at this step?

Accepted Answer

Low-salt buffer disrupts the interaction between RNA and the silica membrane, allowing RNA to be released.

Question 16

Which of the following is a critical step to ensure that only recombinant bacteria are selected after transformation in a gene cloning experiment?

Accepted Answer

Plating the bacteria on a medium containing an antibiotic for which the plasmid carries a resistance gene.

Genetic Engineering: Basic Methods I – Study Notes

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