Ch. 12 - The Cell Cycle

Problem 7

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Chapter 12, Problem 7

Cell A has half as much DNA as cells B, C, and D in a mitotically active tissue. Cell A is most likely in a. G1. b. G2. c. prophase. d. metaphase.

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Understand the stages of the cell cycle: G1, S, G2, and the phases of mitosis (prophase, metaphase, anaphase, telophase).

Recognize that during the G1 phase, the cell has not yet replicated its DNA, so it contains only one set of chromosomes.

Note that during the S phase, DNA replication occurs, doubling the amount of DNA in preparation for cell division.

Acknowledge that in the G2 phase, the cell has twice as much DNA as it did in G1 because it has completed DNA replication.

Conclude that Cell A, having half as much DNA as cells B, C, and D, is most likely in the G1 phase where DNA has not yet been replicated.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Cell Cycle Phases

The cell cycle consists of several phases, including G1, S, G2, and M. During G1, the cell grows and prepares for DNA replication, while in the S phase, DNA is replicated, resulting in two sister chromatids per chromosome. G2 is a preparatory phase for mitosis, and M phase includes mitosis and cytokinesis. Understanding these phases is crucial for determining the DNA content of a cell.

DNA Content in Cell Cycle

DNA content varies throughout the cell cycle. In G1, cells have a diploid amount of DNA (2n), while in the S phase, DNA is duplicated (4n). By G2, the cell still contains 4n DNA, as it prepares for mitosis. During mitosis, specifically in metaphase, the DNA is organized into chromosomes, but the total amount remains the same until cytokinesis occurs.

Mitosis and DNA Distribution

Mitosis is the process by which a cell divides its replicated DNA into two daughter cells. During prophase, chromosomes condense, and the nuclear envelope breaks down, but the DNA content remains at 4n. In metaphase, chromosomes align at the cell's equator, still maintaining this 4n state. Understanding these stages helps clarify why Cell A, with half the DNA, is likely in G1, where it has not yet replicated its DNA.

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Phases of Mitosis

Related Practice

In the cells of some organisms, mitosis occurs without cytokinesis. This will result in a. cells with more than one nucleus. b. cells that are unusually small. c. cells lacking nuclei. d. cell cycles lacking an S phase.

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Textbook Question

Which of the following occurs during apoptosis? (A) lysis of the cell (B) direct contact between signaling cells (C) fragmentation of the DNA (D) release of proteases outside the cell

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Textbook Question

Which of the following occurs during S phase? (A) condensation of the chromosomes (B) replication of the DNA (C) separation of sister chromatids (D) spindle formation

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Textbook Question

The drug cytochalasin B blocks the function of actin. Which of the following aspects of the animal cell cycle would be most disrupted by cytochalasin B? a. spindle formation b. spindle attachment to kinetochores c. cell elongation during anaphase d. cleavage furrow formation and cytokinesis

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Textbook Question

VISUAL SKILLS The light micrograph shows dividing cells near the tip of an onion root. Identify a cell in each of the following stages: prophase, prometaphase, metaphase, anaphase, and telophase. Describe the major events occurring at each stage.

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Textbook Question

DRAW IT Draw one eukaryotic chromosome as it would appear during interphase, during each of the stages of mitosis, and during cytokinesis. Also draw and label the nuclear envelope and any microtubules attached to the chromosome(s).

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