Q: If a eukaryotic chromosome contains $$1.5 \times 10^8$ nucleotide pairs, approximately how long would the DNA be if fully stretched out? (Assume each base pair is 0.34$ nm long.)

$$1.5 \times 10^8$ \times 0.34 \text{ nm} = 5.1 \times 10^7$ \text{ nm} = 5.1 \text{ cm}$$

Question 1

Which experimental result provided the strongest evidence that DNA replication is semiconservative rather than conservative or dispersive?

Accepted Answer

After two rounds of replication in $$^{14}N$$ medium, DNA showed one intermediate and one light band in density gradient centrifugation.

Question 2

What is the functional significance of complementary base pairing in DNA replication?

Accepted Answer

It allows each DNA strand to serve as a template for the synthesis of a new complementary strand.

Question 3

A scientist grows E. coli in $$^{15}N$$ medium, then transfers them to $$^{14}N$$ medium and allows two rounds of DNA replication. What banding pattern would you expect in a density gradient centrifugation experiment?

Accepted Answer

One band at intermediate density and one band at light density.

Question 4

Which of the following best describes the structure of a nucleosome?

Accepted Answer

A core of eight histone proteins with DNA wrapped around it twice.

Question 5

Which property distinguishes heterochromatin from euchromatin in a eukaryotic cell?

Accepted Answer

Heterochromatin is highly condensed and generally inaccessible for gene expression.

Question 6

During DNA replication, which enzyme is primarily responsible for unwinding the double helix?

Accepted Answer

Helicase

Question 7

If a eukaryotic chromosome contains $$1.5 	imes 10^8$ nucleotide pairs, approximately how long would the DNA be if fully stretched out? (Assume each base pair is 0.34$ nm long.)

Accepted Answer

$$1.5 	imes 10^8$ 	imes 0.34 	ext{ nm} = 5.1 	imes 10^7$ 	ext{ nm} = 5.1 	ext{ cm}$$

Question 8

Which of the following best explains why DNA can serve as its own template during replication?

Accepted Answer

The two strands of DNA are complementary, so each can direct the synthesis of its partner.

Question 9

Which of the following statements about chromatin structure is correct?

Accepted Answer

Chromatin is a complex of DNA and proteins that can exist in more or less condensed forms depending on the cell cycle stage.

Question 10

A mutation causes the loss of histone H1 in a eukaryotic cell. Which chromatin structure would be most directly affected?

Accepted Answer

The formation of the 30 nm fiber would be disrupted.

Question 11

Which of the following best describes the role of the nuclear lamina in eukaryotic cells?

Accepted Answer

It provides structural support and helps organize chromatin within the nucleus.

Question 12

During which phase of the cell cycle does DNA replication occur, and how is this related to chromatin structure?

Accepted Answer

DNA replication occurs during the S phase, when chromatin is less condensed to allow access to replication machinery.

Question 13

Which of the following would most likely result if histone tails were chemically modified to prevent their interaction with DNA?

Accepted Answer

Chromatin would remain in a more open, euchromatin-like state, increasing gene expression.

Question 14

Which of the following is a direct consequence of the semiconservative model of DNA replication?

Accepted Answer

Each daughter DNA molecule consists of one parental strand and one newly synthesized strand.

Question 15

Which of the following best explains why E. coli DNA is supercoiled and densely packed into the nucleoid region?

Accepted Answer

The DNA molecule is much longer than the cell itself and must be compacted to fit inside.

Question 16

A researcher treats human chromosomes with molecular tags that cause each chromosome pair to appear a different color. What does this experiment demonstrate about chromatin organization?

Accepted Answer

Chromatin from different chromosomes occupies discrete areas of the nucleus.

Section 8: The Molecular Basis of Inheritance – DNA Structure, Replication, and Chromosome Organization

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