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Chapter 11: Problem 2

Which statement about the cell cycle is not true? a. It consists of interphase, mitosis, and cytokinesis. b. The cell's DNA replicates during G1. c. A cell can remain in G1 for weeks or much longer. d. DNA is not replicated during G2. e. Cells enter the cell cycle as a result of internal or external signals.

Short Answer

Expert verified
Statement b is not true.

Step by step solution

01

Understanding the Cell Cycle

The cell cycle is the sequence of events that a cell undergoes, resulting in its division and replication. It consists of several stages: interphase (which includes G1, S, and G2 phases), mitosis, and cytokinesis.
02

Examining Each Statement

We will examine each statement to determine its accuracy based on our understanding of the cell cycle. - Statement a: The cell cycle consists of interphase, mitosis, and cytokinesis, which is true. - Statement b: The cell's DNA actually replicates during the S phase, not G1, making this statement false. - Statement c: A cell can remain in G1 for various periods, so this statement is true. - Statement d: DNA is not replicated during G2; the replication occurs in the S phase, so this statement is true. - Statement e: Cells indeed enter the cell cycle due to internal or external signals, making this statement true.
03

Identifying the Incorrect Statement

After reviewing each statement, we determine that statement b is not true, as DNA replication occurs in the S phase of interphase, not during the G1 phase.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Interphase
Interphase is the longest period of the cell cycle where a cell spends most of its life. During this phase, the cell is not dividing but is instead preparing for the next steps of cell division. Interphase is crucial as it ensures that the cell grows properly and acquires all the necessary components for mitosis.
  • It includes three distinct phases: G1, S, and G2.
  • The cell undergoes significant growth and replication of organelles.
  • While DNA is replicated in the S phase, overall cell preparation is completed during G1 and G2.
Interphase sets the stage for a successful cell division by ensuring the cell's resources are doubled and ready.
Mitosis
Mitosis is the process where a single cell divides into two genetically identical daughter cells. It ensures that each new cell receives an exact copy of the parent cell's DNA. This stage consists of several sub-phases: prophase, metaphase, anaphase, and telophase.
  • Prophase: Chromosomes condense and become visible.
  • Metaphase: Chromosomes line up in the middle of the cell.
  • Anaphase: Chromosomes begin to pull apart to opposite ends of the cell.
  • Telophase: Two new nuclear membranes start to form around each set of chromosomes.
Mitosis ensures continuity of genetic information across generations of cells.
Cytokinesis
Cytokinesis is the final stage of cell division where the cytoplasm of a single eukaryotic cell divides to form two daughter cells. While mitosis divides the nucleus, cytokinesis is responsible for splitting the cell membrane and other cell components.
  • This stage follows mitosis and completes the cell division process.
  • In animal cells, the cell membrane pinches inward, creating a cleavage furrow that leads to separation.
  • In plant cells, a cell plate forms between the two new cells, eventually becoming a new cell wall.
Cytokinesis ensures that each daughter cell has the organelles and cytoplasm it needs to function independently.
DNA Replication
DNA replication is a vital process that occurs during the S phase of interphase. This is when the cell's DNA is copied to ensure that each new cell receives a complete set of chromosomes. Without accurate DNA replication, new cells would lack the genetic information needed for survival and function.
  • The process begins by unwinding the double helix of DNA.
  • Each strand serves as a template for creating a complementary strand.
  • Enzymes such as DNA polymerase are essential in adding new nucleotides to form new DNA strands.
Successful DNA replication ensures genetic consistency and diversity through precise copying of genetic material.
G1 Phase
The G1 phase is the first of the three phases of interphase in the cell cycle. During G1, the cell grows in size and synthesizes mRNA and proteins essential for DNA synthesis. This phase is critical for cell growth and the production of organelles.
  • This phase follows cell division and precedes DNA synthesis.
  • It is considered a period where the cell commits to division or enters a resting state called G0.
  • Regulatory checkpoints ensure that the cell is ready for the S phase.
The G1 phase prepares the cell for subsequent DNA replication and mitosis.
S Phase
The S phase, or synthesis phase, is where DNA replication occurs, allowing the cell to have enough DNA for two daughter cells.
  • During this phase, each chromosome is duplicated, resulting in two sister chromatids.
  • Efficient DNA replication requires various enzymes like helicase and ligase.
  • The integrity of the DNA is checked and repaired during and after replication.
The S phase is crucial because it ensures that both daughter cells receive an identical copy of the DNA.
G2 Phase
In the G2 phase, cells experience further growth and prepare for mitosis. It follows the S phase and precedes mitosis, serving as the final checkpoint before cell division.
  • During G2, cells continue to grow and produce proteins necessary for mitosis.
  • This phase allows for repair of any DNA damage detected after replication.
  • The cell ensures that all proteins and organelles needed for cell division are available.
G2 is critical to ensuring that cells are fully prepared to divide, preventing errors that could lead to malfunctioning or nonviable cells.

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Most popular questions from this chapter

Which statement about eukaryotic chromosomes is not true? a. They sometimes consist of two chromatids. b. They sometimes consist only of a single chromatid. c. They normally possess a single centromere. d. They consist only of proteins. e. During metaphase they are visible under the light microscope.

Studying the cell cycle is much easier if the cells under investigation are synchronous-all in the same stage of the cell cycle. Some populations of cells are naturally synchronous. The anther (male sex organ) of a lily plant contains cells that become pollen grains (male gametes). As anthers develop in the flower, their lengths correlate precisely with the stage of the meiotic cycle in those cells. An anther that is 1.5 millimeters long, for example, contains cells in early prophase I. How would you use lily anthers to investigate the roles of cyclins and Cdk's in the meiotic cell cycle?

Which statement about mitosis is not true? a. A single nucleus gives rise to two identical daughter nuclei. b. The daughter nuclei are genetically identical to the parent nucleus. c. The centromeres separate at the onset of anaphase. d. Homologous chromosomes synapse in prophase. e. The centrosomes organize the microtubules of the spindle fibers.

The tumor suppressor \(p 53\) normally acts by stimulating the expression of \(\mathrm{p} 21 .\) Explain why loss of \(\mathrm{p} 53\) function would lead to uncontrolled cell division.

Contrast mitotic prophase and prophase I of meiosis. Contrast mitotic anaphase and anaphase I of meiosis.
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