Question 1

Which experiment first demonstrated that a 'transforming principle' could transfer genetic information between bacteria, and what was the key result?

Accepted Answer

The Griffith experiment; mice injected with heat-killed S strain and living R strain died, indicating transformation.

Question 2

Which chemical bond is responsible for the stability of the DNA backbone, and why is this important for forensic science?

Accepted Answer

Phosphodiester bond; it is strong and resists degradation, allowing DNA to persist in harsh conditions.

Question 3

Which of the following best describes the directionality of a DNA strand?

Accepted Answer

It has a 5’ phosphate group at one end and a 3’ hydroxyl group at the other.

Question 4

According to Chargaff’s rules, if a DNA sample contains 30% adenine, what percentage of guanine would you expect?

Accepted Answer

$$20\%$$

Question 5

Which pair of nitrogenous bases forms the most stable bond in DNA, and how many hydrogen bonds are involved?

Accepted Answer

Guanine and cytosine; 3 hydrogen bonds

Question 6

Which historical discovery directly led to the conclusion that DNA, not protein, is the genetic material in viruses?

Accepted Answer

Hershey and Chase’s experiment using radioactive isotopes to label DNA and protein in bacteriophages

Question 7

What is the main structural difference between deoxyribose and ribose, and how does this affect DNA and RNA?

Accepted Answer

Deoxyribose lacks an oxygen atom at the 2’ carbon, making DNA more stable than RNA.

Question 8

A scientist is transfecting animal cells with a gene that confers antibiotic resistance. What process allows only the successfully transfected cells to survive?

Accepted Answer

Selection using the antibiotic to kill non-transfected cells

Question 9

Which of the following best explains why DNA is described as 'antiparallel'?

Accepted Answer

The two strands run in opposite directions: one 5’ to 3’, the other 3’ to 5’.

Question 10

If a DNA double helix contains 100 base pairs, how many nanometers long is one complete turn of the helix?

Accepted Answer

$$3.4\ \mathrm{nm}$$

Question 11

Which of the following is a purine base found in DNA?

Accepted Answer

Adenine

Question 12

What is the significance of the major and minor grooves in the DNA double helix?

Accepted Answer

They provide binding sites for proteins that regulate gene expression.

Question 13

Which of the following statements about chromosomes is correct?

Accepted Answer

Each chromosome consists of a single, long molecule of duplex DNA and associated proteins.

Question 14

Which of the following best describes the chemical structure of a phosphodiester bond in DNA?

Accepted Answer

A covalent bond between the 5’ phosphate of one nucleotide and the 3’ hydroxyl of another.

Question 15

Which of the following is a real-world application that relies on the chemical stability of DNA?

Accepted Answer

Forensic identification from old biological samples

Question 16

A mutation changes a cytosine to a thymine in a DNA strand. Which type of base pairing is disrupted?

Accepted Answer

A triple hydrogen bond between cytosine and guanine

Question 17

Which of the following best explains why RNA is less stable than DNA in cells?

Accepted Answer

RNA contains a 2’ hydroxyl group, making it more susceptible to hydrolysis.

Question 18

Which of the following is NOT a feature of the Watson-Crick model of DNA?

Accepted Answer

Sugar-phosphate backbones are equally spaced, resulting in no grooves.

Question 19

If a segment of DNA has the sequence 5’-TATTCCGA-3’, what is the complementary sequence?

Accepted Answer

3’-ATAAGGCT-5’

Molecular Basis of Heredity: DNA Structure and Function

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