Question 1

Which result from Griffith's experiment provided the strongest evidence for the process of transformation in bacteria?

Accepted Answer

Mice injected with a mixture of heat-killed S strain and live R (rough) strain bacteria died.

Question 2

In the Hershey-Chase experiment, why was phosphorus-32 ($^{32}P$) used to label DNA and sulfur-35 ($^{35}S$) used to label protein?

Accepted Answer

$^{32}P$ is incorporated into the phosphate backbone of DNA, while $^{35}S$ is found in the amino acids of proteins.

Question 3

Chargaff’s rules state that in double-stranded DNA, the amount of adenine (A) always equals the amount of thymine (T), and the amount of guanine (G) equals the amount of cytosine (C). If a DNA sample contains 30% adenine, what percentage of guanine does it contain?

Accepted Answer

$20\%$

Question 4

Which of the following best explains why telomerase activity is important in stem cells and cancer cells?

Accepted Answer

Telomerase prevents the loss of genetic information by extending telomeres, allowing cells to divide indefinitely.

Question 5

Which step in the Polymerase Chain Reaction (PCR) is responsible for separating the two strands of DNA?

Accepted Answer

Denaturation at $94-96^\circ C$

Question 6

A scientist wants to clone a gene using bacteria. Which sequence of steps is correct for creating recombinant DNA and producing genetically modified bacteria?

Accepted Answer

Cut gene with restriction enzyme, insert into plasmid, transform bacteria, select for antibiotic resistance.

Question 7

During gel electrophoresis, DNA fragments are separated based on which property?

Accepted Answer

Size (length of DNA fragments)

Question 8

Which of the following best describes the role of complementary base pairing in DNA replication?

Accepted Answer

It ensures that each new DNA molecule is an exact copy of the original by matching A with T and G with C.

Question 9

A forensic scientist is analyzing a crime scene sample using DNA fingerprinting. Which genetic markers are most commonly used for this purpose?

Accepted Answer

Short tandem repeats (STRs)

Question 10

Which of the following statements about Rosalind Franklin’s contribution to the discovery of DNA structure is correct?

Accepted Answer

She used X-ray diffraction to reveal the helical structure of DNA.

Question 11

Which process is used to detect specific DNA sequences in a mixture after gel electrophoresis?

Accepted Answer

Southern blotting

Question 12

If a mutation causes the loss of telomerase activity in a cell line, what is the most likely long-term consequence?

Accepted Answer

Progressive shortening of telomeres leading to cellular aging and eventual cell death

Question 13

Which of the following best explains why bacteriophages were used in the Hershey-Chase experiment?

Accepted Answer

They inject only their genetic material into bacteria, allowing researchers to distinguish between DNA and protein as the hereditary material.

Question 14

Which of the following is NOT a direct application of gel electrophoresis?

Accepted Answer

Measuring the rate of DNA replication in living cells

Question 15

A researcher is using PCR to amplify a gene. After 5 cycles, how many copies of the target DNA sequence will be present, assuming perfect doubling each cycle and starting with 1 molecule?

Accepted Answer

$2^5 = 32$ copies

Question 16

Which of the following best describes the significance of the double helix structure of DNA?

Accepted Answer

It allows for complementary base pairing, enabling accurate replication and repair.

Question 17

Which enzyme is responsible for synthesizing new DNA strands during PCR?

Accepted Answer

DNA polymerase

Question 18

Which of the following is a key reason why telomeres are important for chromosome stability?

Accepted Answer

They protect the ends of chromosomes from degradation and fusion with other chromosomes.

Question 19

Which of the following best describes the process of transformation in bacteria as discovered by Griffith?

Accepted Answer

Uptake of genetic material from the environment, resulting in a change in phenotype.

Molecular Genetics: Experiments, DNA Structure, and Biotechnology

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