Question 1

Which of the following best explains why DNA fragments move toward the positive electrode during agarose gel electrophoresis?

Accepted Answer

DNA fragments are negatively charged due to their phosphate backbone and are attracted to the positive electrode.

Question 2

During agarose gel electrophoresis, which size of DNA fragments will migrate the farthest from the wells, and why?

Accepted Answer

Small fragments, because they can move more easily through the gel matrix.

Question 3

A student loads DNA samples into the wells at the cathode (negative) end of the gel. After running the gel, no bands are visible. Which of the following is the most likely explanation?

Accepted Answer

The DNA migrated toward the anode (positive) end and out of the gel.

Question 4

Why is a KB ladder (DNA size marker) loaded into one lane of the agarose gel during electrophoresis?

Accepted Answer

To provide a reference for estimating the sizes of DNA fragments in other lanes.

Question 5

If a circular plasmid DNA is cut by a restriction enzyme at two sites, how many fragments will be produced?

Accepted Answer

$$3$$

Question 6

A student wants to estimate the size of an unknown DNA fragment. She measures the migration distance as $$35 mm. $$Using the standard curve, she finds that this distance corresponds to $$1,500$$ base pairs. What is the size of her DNA fragment?

Accepted Answer

$$1,500$$ base pairs

Question 7

Which of the following best describes the function of restriction enzymes in DNA fingerprinting?

Accepted Answer

They cut DNA at specific sequences, generating fragments of varying lengths.

Question 8

Why is it important to use a new pipet tip for each DNA sample when loading the gel?

Accepted Answer

To prevent contamination between samples, which could lead to inaccurate results.

Question 9

Suppose you observe that the DNA bands in the crime scene lane and suspect 3 lane are identical in both number and position. What is the most reasonable conclusion?

Accepted Answer

Suspect 3's DNA matches the crime scene DNA, suggesting they may be the source.

Question 10

If a linear DNA molecule is cut by a restriction enzyme at three sites, how many fragments will result?

Accepted Answer

$$4$$

Question 11

Which of the following is a critical safety step when working with ethidium bromide in the lab?

Accepted Answer

Wear nitrile gloves at all times to avoid skin contact.

Question 12

A student forgets to add loading dye to her DNA samples before loading them into the gel. What is the most likely outcome?

Accepted Answer

The DNA samples will diffuse out of the wells and may not enter the gel properly.

Question 13

Which of the following best describes the relationship between migration distance and fragment size in agarose gel electrophoresis?

Accepted Answer

Migration distance is inversely proportional to the logarithm of fragment size.

Question 14

Why is it necessary to create a standard curve when analyzing DNA fragment sizes?

Accepted Answer

To accurately estimate unknown fragment sizes based on their migration distances.

Question 15

If two DNA samples produce the same number of bands, but the bands are at different positions, what does this indicate?

Accepted Answer

The samples have the same number of restriction sites but different fragment sizes.

Question 16

A student measures the migration distances of the KB ladder bands and plots them against their known sizes. What type of graph should she use to best represent the relationship?

Accepted Answer

A semi-logarithmic graph, with migration distance on the x-axis and log(fragment size) on the y-axis.

Question 17

Which of the following is NOT a reason for using agarose gel in DNA electrophoresis?

Accepted Answer

Agarose chemically reacts with DNA to produce visible bands.

Question 18

After running an electrophoresis gel, you observe that all DNA bands are very close to the wells and have not migrated far. Which of the following is the most likely cause?

Accepted Answer

The voltage was set too low or the run time was too short.

Question 19

Which of the following best explains why gloves are required when handling DNA samples and gels in this lab?

Accepted Answer

To protect both the student from hazardous chemicals and the samples from contamination.

Question 20

If a DNA sample produces a single band after restriction digestion and electrophoresis, what can you infer about the number of restriction sites in the original DNA?

Accepted Answer

There were no restriction sites for the enzyme used.

Bio 100 LAB 5

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