Question 1

Which enzyme is responsible for separating the two strands of DNA during replication in vivo, and what is its equivalent in PCR?

Accepted Answer

Helicase in vivo; heat denaturation in PCR

Question 2

During PCR, what are the primers made of, and how does this differ from DNA replication in vivo?

Accepted Answer

Primers are made of DNA in PCR, but RNA in vivo

Question 3

Which of the following best explains why ligase is not required during PCR?

Accepted Answer

PCR amplifies short DNA fragments that do not require joining of Okazaki fragments

Question 4

Huntington's Disease is caused by which molecular mechanism?

Accepted Answer

Replication slippage leading to expansion of CAG repeats

Question 5

You are designing a PCR test to detect the presence of a gene. After running agarose gel electrophoresis, you observe a single band at the expected size in the test sample and positive control, but no band in the negative control. What does this indicate?

Accepted Answer

The gene is present in the test sample

Question 6

Which of the following is the correct order of steps in an RT-PCR reaction for detecting an RNA virus such as SARS-CoV-2?

Accepted Answer

Isolate mRNA $\rightarrow$ Use reverse transcriptase to generate cDNA $\rightarrow$ Perform conventional PCR $\rightarrow$ Run an agarose gel electrophoresis

Question 7

A patient is suspected to have Huntington's Disease. PCR amplification of the gene region followed by gel electrophoresis shows a larger band compared to a healthy control. What is the most likely explanation?

Accepted Answer

Expansion of CAG repeats in the Huntington gene

Question 8

Why is Taq polymerase used in PCR instead of a typical DNA polymerase from E. coli?

Accepted Answer

Taq polymerase is thermostable and can withstand the high temperatures used in PCR

Question 9

In a PCR reaction, what is the purpose of the annealing step, and at what approximate temperature does it occur?

Accepted Answer

Allows primers to bind to the template DNA; occurs at approximately $55^\circ C$

Question 10

A researcher wants to determine if a gene is present and also estimate its size. Which combination of techniques should they use?

Accepted Answer

PCR followed by agarose gel electrophoresis

Question 11

If you are testing nasal swab samples for SARS-CoV-2 using RT-PCR, which of the following would be an appropriate negative control?

Accepted Answer

A sample containing all reagents except the RNA template

Question 12

Which of the following statements about PCR primers is correct?

Accepted Answer

Primers determine the specific region of DNA that will be amplified

Question 13

A PCR product is 500 base pairs long. If the initial amount of template DNA is doubled, what is the expected effect on the amount of PCR product after 30 cycles, assuming 100% efficiency?

Accepted Answer

The final amount of PCR product will also double

Question 14

Which of the following best describes the inheritance pattern of Huntington's Disease based on PCR gel electrophoresis data showing affected individuals in every generation?

Accepted Answer

Autosomal dominant

Question 15

During RT-PCR, what is the role of reverse transcriptase?

Accepted Answer

To synthesize complementary DNA (cDNA) from an RNA template

Question 16

A PCR reaction is set up to amplify a region of DNA flanked by the following primers: 5'-AGCTAGT-3' and 5'-TCGATCA-3'. If the template DNA is 1000 base pairs long and the primers bind at positions 100 and 600, what is the expected size of the PCR product?

Accepted Answer

$600 - 100 = 500$ base pairs

Question 17

Which of the following is a key similarity between DNA replication in vivo and PCR in vitro?

Accepted Answer

Both require a DNA polymerase to synthesize new DNA strands

Question 18

If a PCR reaction fails to produce any product, which of the following is the LEAST likely cause?

Accepted Answer

The DNA polymerase was added in excess

Question 19

In the context of PCR, what is the main function of running an agarose gel electrophoresis after amplification?

Accepted Answer

To separate DNA fragments by size and visualize the PCR products

Question 20

A scientist is using RT-PCR to detect SARS-CoV-2 RNA in patient samples. Which result would indicate a positive test for the virus?

Accepted Answer

A band of the expected size appears in the test sample and positive control, but not in the negative control

DNA Replication, PCR, and Genetic Testing: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards