Chromosomes and Molecular Biology Practice Quiz (15 questions)

1. Researchers heat-kill virulent bacteria, mix them with nonvirulent bacteria, and inject the mixture into mice. What outcome matches Griffith’s transformation experiment?

A. The heat-killed cells alone cause pneumonia, and the mice die

B. Some nonvirulent cells become virulent, and the mice die of pneumonia

C. The nonvirulent cells stay harmless, and the mice survive

D. Some virulent cells become nonvirulent, and the mice survive

Answer: (B)

Explanation

In Griffith’s experiment, material from the heat-killed virulent bacteria enabled some nonvirulent cells to become virulent, and the injected mice died of pneumonia. The heat-killed cells alone did not explain the transformation, and the nonvirulent cells did not remain harmless in the mixture.

2. What did Hershey and Chase’s 1952 T2 phage blender experiment establish about viral DNA?

A. It enters bacterial cells and is needed to make new viral particles

B. It is produced by bacterial cells after the phage infection

C. It is unnecessary for producing new viral particles

D. It remains outside bacterial cells while viral protein enters

Answer: (A)

Explanation

The experiment established that phage DNA enters bacterial cells and is required for synthesizing new viral particles. The protein coat remaining outside is not the genetic material that directs this production, and bacterial DNA is not the viral genetic material at issue.

3. A molecule contains a sugar and a nitrogenous base but no phosphate group; what is it classified as?

A. A phosphodiester bond

B. A DNA strand

C. A nucleotide

D. A nucleoside

Answer: (D)

Explanation

A nucleoside consists of a sugar and a base. A nucleotide includes one or more phosphate groups, so calling the phosphate-free molecule a nucleotide confuses the two terms.

4. A nucleoside receives two phosphate groups; what is the resulting molecule called?

A. A phosphodiester linkage

B. A nucleotide

C. A nitrogenous base

D. A nucleoside

Answer: (B)

Explanation

A nucleotide is a nucleoside with one or more phosphate groups, so adding two phosphates produces a nucleotide. A nucleoside lacks those phosphate groups, while a phosphodiester linkage is a bond in the strand backbone.

5. A DNA polymerase is extending a strand by adding bases to the sugar’s available 3′-OH. In which direction will the new strand grow?

A. From 5′ to 5′

B. From 3′ to 5′

C. From 3′ to 3′

D. From 5′ to 3′

Answer: (D)

Explanation

Because each new base is added to the 3′-OH, DNA strand growth proceeds in the 5′-to-3′ direction. The 3′-to-5′ choice reverses the direction implied by the addition site.

6. A double-stranded DNA sample contains 18% adenine. What percentage of the sample is guanine?

A. 41%

B. 32%

C. 18%

D. 64%

Answer: (B)

Explanation

Chargaff’s rule makes adenine equal to thymine and guanine equal to cytosine, so 36% is A plus T and the remaining 64% is split equally between G and C. The 18% choice equates G with A, while the other values do not follow the equal-pair proportions.

7. What feature of DNA contributes to double-helix stability through interactions between bases on opposite strands?

A. Phosphodiester bonds in the backbone

B. Hydrogen bonds between paired bases

C. Base stacking along each strand

D. Complementary pairing without base bonds

Answer: (B)

Explanation

Hydrogen bonds between bases on opposite strands contribute to the stability of the double helix. Base stacking occurs between bases on the same strand, while phosphodiester bonds link the backbone.

8. After a DNA molecule replicates, how are the strands distributed between the two resulting molecules under semiconservative replication?

A. The original strands separate without new strands being made

B. Each molecule has two newly synthesized strands

C. One molecule has both original strands and the other has two new strands

D. Each molecule has one original strand and one newly synthesized strand

Answer: (D)

Explanation

In semiconservative replication, each original strand serves as a template for a new strand, leaving each resulting molecule with one old and one new strand. Keeping both old strands together or producing two new strands per molecule misstates this distribution.

9. During replication, a DNA polymerase adds bases complementary to the template strand. What does this pairing help preserve?

A. The fidelity of the copied DNA sequence

B. The occurrence of base-installation errors

C. The number of DNA molecules produced

D. The stability of the double helix through stacking

Answer: (A)

Explanation

Complementary base pairing helps preserve the fidelity of DNA replication by guiding accurate sequence copying. Base-installation errors are mutations, while helix stability and the number of products are different aspects of DNA structure and replication.

10. Which sequence represents the central dogma’s flow of genetic information?

A. DNA to protein to RNA

B. DNA to RNA to protein

C. RNA to DNA to protein

D. Protein to RNA to DNA

Answer: (B)

Explanation

The central dogma describes genetic information flowing from DNA to RNA to protein. Reversing DNA and RNA changes the sequence, while the other choices put protein in the wrong position.

11. A cell uses a DNA strand to make an RNA molecule, then uses that RNA to build a protein. Which processes occur in that order?

A. Transcription, then translation

B. Translation, then replication

C. Replication, then transcription

D. Translation, then transcription

Answer: (A)

Explanation

Transcription uses DNA as a template to produce RNA, and translation uses RNA to produce protein. Reversing the processes confuses their sequence, while replication copies DNA rather than producing RNA.

12. A researcher identifies a nucleic acid whose sugar is ribose. Which molecule does this feature indicate?

A. A DNA molecule containing thymine

B. DNA

C. A double-stranded DNA molecule

D. RNA

Answer: (D)

Explanation

RNA contains ribose, whereas DNA contains deoxyribose. DNA’s association with thymine or a double-stranded structure does not change its sugar.

13. A nucleic acid sample contains uracil instead of thymine. Which set of bases is expected in that molecule?

A. Adenine, uracil, thymine, and guanine

B. Adenine, thymine, cytosine, and guanine

C. Uracil, thymine, cytosine, and guanine

D. Adenine, uracil, cytosine, and guanine

Answer: (D)

Explanation

RNA uses adenine, uracil, cytosine, and guanine; thymine is the corresponding DNA base. The alternatives either retain thymine or substitute uracil for another base.

14. An unknown nucleic acid is smaller and single-stranded. Which identification best fits these characteristics?

A. Large, single-stranded DNA

B. Large, double-stranded DNA

C. RNA

D. DNA

Answer: (C)

Explanation

RNA is smaller and single-stranded, while DNA is very large and double-stranded. The other choices mix or apply DNA’s size and strand characteristics.

15. Which researcher first isolated a phosphorus-containing material from white blood cell nuclei in 1869 and named it “nuclein”?

A. Frederick Griffith

B. Erwin Chargaff

C. Friedrich Miescher

D. James Watson

Answer: (C)

Explanation

Friedrich Miescher discovered the material later identified as DNA in 1869 and named it “nuclein.” Griffith investigated bacterial transformation, Chargaff identified base relationships, and Watson helped determine DNA’s structure.