Question 1

Which of the following best describes the role of restriction enzymes in molecular biology experiments?

Accepted Answer

They cut DNA molecules at specific nucleotide sequences, generating fragments for analysis.

Question 2

During gel electrophoresis, why do smaller DNA fragments travel farther than larger ones?

Accepted Answer

Smaller fragments move more easily through the porous gel matrix.

Question 3

A student loads a DNA sample into a gel and applies an electric current. What is the direction of DNA movement, and why?

Accepted Answer

Toward the positive pole, because DNA is negatively charged due to its phosphate backbone.

Question 4

Which chemical is commonly used to visualize DNA in agarose gels, and what is a major safety concern associated with its use?

Accepted Answer

Ethidium bromide; it is a mutagen and potential carcinogen.

Question 5

A plasmid is cut with EcoRI, which recognizes the sequence $$5'	ext{GAATTC}3'$$ and cuts between G and A. If the plasmid is circular and has only one EcoRI site, how many DNA bands do you expect to see after gel electrophoresis?

Accepted Answer

One band, because the plasmid is linearized into a single fragment.

Question 6

Why is it important to wear gloves when working with ethidium bromide in the lab?

Accepted Answer

To avoid direct skin contact with a mutagenic and potentially carcinogenic chemical.

Question 7

Which of the following best explains why a DNA ladder is loaded alongside experimental samples in gel electrophoresis?

Accepted Answer

To provide a reference for determining the size of DNA fragments in base pairs.

Question 8

A student accidentally heats ethidium bromide. What is the primary safety concern in this scenario?

Accepted Answer

Heated ethidium bromide can release toxic fumes.

Question 9

Which of the following is a correct pairing of DNA bases in the double helix?

Accepted Answer

Adenine pairs with thymine, guanine pairs with cytosine.

Question 10

A researcher uses both EcoRI and SalI to cut a plasmid. If the plasmid contains one site for each enzyme, how many bands are expected after gel electrophoresis?

Accepted Answer

Two bands, because the plasmid is cut into two fragments.

Question 11

Which of the following best describes the function of the power supply in gel electrophoresis?

Accepted Answer

It provides the electrical current that drives the migration of DNA through the gel.

Question 12

Why is it important to avoid touching other surfaces with gloves contaminated by ethidium bromide?

Accepted Answer

To prevent spreading a mutagenic chemical to other surfaces and increasing exposure risk.

Question 13

Which of the following statements about the phosphate backbone of DNA is correct?

Accepted Answer

It gives DNA a negative charge, allowing it to migrate toward the positive electrode during electrophoresis.

Question 14

A student is using a micropipette to load DNA samples into a gel. What is the most important reason for practicing proper pipetting technique?

Accepted Answer

To ensure accurate and consistent sample loading, preventing cross-contamination and uneven bands.

Question 15

Which of the following is a real-world application of restriction enzymes?

Accepted Answer

Creating recombinant DNA molecules for gene therapy.

Question 16

If a DNA fragment is 1000 base pairs (bp) and another is 500 bp, which will travel farther in an agarose gel and why?

Accepted Answer

The 500 bp fragment, because smaller fragments move more easily through the gel matrix.

Question 17

Which of the following best describes the relationship between genes, proteins, and function in molecular biology?

Accepted Answer

Genes encode proteins, which determine cellular function.

Question 18

A scientist wants to amplify a specific DNA sequence from a small sample. Which technique should they use?

Accepted Answer

Polymerase Chain Reaction (PCR)

Question 19

Which safety practice is NOT recommended when working with ethidium bromide?

Accepted Answer

Heating ethidium bromide to speed up staining.

Question 20

Which of the following is a pyrimidine found in DNA?

Accepted Answer

Thymine

Molecular Biology Lab: DNA, Restriction Enzymes, and Gel Electrophoresis

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