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Chapter 2: Problem 9

Describe the phases of the cell cycle and the events that characterize each phase.

Short Answer

Expert verified
Answer: The cell cycle consists of interphase and mitosis (or M phase). Interphase includes the G1 phase (cell growth and protein synthesis), S phase (DNA replication), and G2 phase (additional growth and preparation for mitosis). Mitosis is divided into prophase (chromatin condensation and spindle formation), metaphase (chromosome alignment), anaphase (sister chromatid separation), and telophase (chromosome decondensation and nuclear envelope formation). Cytokinesis, the division of the cytoplasm, occurs after mitosis to produce two daughter cells.

Step by step solution

01

Describe Interphase

Interphase is the longest part of the cell cycle and is the phase where the cell grows and prepares for cell division. It is subdivided into three phases: G1, S, and G2.
02

Describe the G1 Phase

The G1 phase, or "Gap 1" phase, is the first phase of interphase. During the G1 phase, the cell grows in size, synthesizes new proteins, and produces more organelles. This phase is crucial for the cell to prepare for DNA replication in the next phase.
03

Describe the S Phase

The S phase, or "Synthesis" phase, is the second phase of interphase. During this phase, DNA replication occurs. By the end of the S phase, the cell has doubled its amount of DNA, ensuring that each daughter cell will receive a complete set of genetic information during mitosis.
04

Describe the G2 Phase

The G2 phase, or "Gap 2" phase, follows DNA replication. In this phase, the cell continues to grow and prepares for mitosis by synthesizing additional proteins, particularly those needed for chromosome organization and spindle formation. The G2 phase ensures that the cells have all the necessary components for mitosis to occur successfully.
05

Describe Mitosis (M Phase)

Mitosis, or the M phase, is the process of cell division where the nucleus divides, and the replicated DNA is distributed equally to two daughter cells. Mitosis can be further divided into four stages: prophase, metaphase, anaphase, and telophase.
06

Describe Prophase

During prophase, the chromatin condenses into visible chromosomes, consisting of two sister chromatids joined at the centromere. The nucleolus disappears, and the nuclear envelope starts to break down. The mitotic spindle, consisting of microtubules, begins to form and extend from the two centrosomes, which migrate to opposite sides of the cell.
07

Describe Metaphase

Metaphase is characterized by the alignment of chromosomes along the cell's equatorial plane, also known as the metaphase plate. The spindle fibers from each centrosome attach to the centromeres of the chromosomes, ensuring that each daughter cell will receive one chromatid from each chromosome.
08

Describe Anaphase

During anaphase, sister chromatids are pulled apart by the spindle fibers and move towards opposite poles of the cell. The chromosomes are separated into two groups at each pole, and the cell starts to elongate.
09

Describe Telophase

In telophase, the chromosomes decondense back into chromatin, and a new nuclear envelope forms around each set of chromosomes. The nucleolus reappears, the mitotic spindle breaks down, and the cell continues to elongate.
10

Describe Cytokinesis

Cytokinesis is the final step in the cell cycle, during which the cytoplasm divides, and two new daughter cells are formed. In animal cells, a cleavage furrow forms, while in plant cells, a cell plate is formed to create the new cell walls. After cytokinesis, the daughter cells enter the G1 phase of interphase and the cell cycle begins anew.

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Most popular questions from this chapter

In this chapter, we focused on how chromosomes are distributed during cell division, both in dividing somatic cells (mitosis) and in gamete- and spore- forming cells (meiosis). We found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, answer the following questions. (a) How do we know that chromosomes exist in homologous pairs? (b) How do we know that DNA replication occurs during interphase, not early in mitosis? (c) How do we know that mitotic chromosomes are derived from chromatin?

Contrast the chromatin fiber with the mitotic chromosome. How are the two structures related?

You are given a metaphase chromosome preparation (a slide) from an unknown organism that contains 12 chromosomes. Two that are clearly smaller than the rest appear identical in length and centromere placement. Describe all that you can about these chromosomes.

During oogenesis in an animal species with a haploid number of \(6,\) one dyad undergoes nondisjunction during meiosis II. Following the second meiotic division, this dyad ends up intact in the ovum. How many chromosomes are present in (a) the mature ovum and (b) the second polar body? (c) Following fertilization by a normal sperm, what chromosome condition is created?

Define and discuss these terms: (a) synapsis, (b) bivalents, (c) chiasmata, (d) crossing over, (e) sister chromatids, (f) tetrads, \((g)\) dyads, (h) monads.
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