4 Pre-Lab Exercise 4-4 The Cell Cycle Use your text and lab manual to answer the following questions about the cell cycle and mitosis. 1. Describe the following stages of the cell cycle: a. G1 the initial growth phase during which the cell grows, develops, & carries out activities that are specific to that cell type. b. S the period during which the cell’s DNA is replicated. “S”: Synthesis because another copy of DNA is synthesized. c. G2 the 2nd growth phase during which the cell makes its final preparations for division. d. M the phase during which the cell, “mother cell” undergoes mitosis & divides its replicated DNA among 2 identical daughter cells. 2. Describe the events occurring in the cell in each of the phases of mitosis in Table 4.1. TABLE 4.1 Stages of Mitosis Stage of Mitosis Events Taking Place in the Cell Cell Appearance Prophase Metaphase Anaphase Telophase 74 Exploring Anatomy & Physiology in the Laboratory
The Correct Answer and Explanation is:
Stages of the Cell Cycle:
a. G1 (Gap 1):
- Description: This is the initial phase of the cell cycle where the cell grows and carries out its normal functions. During G1, the cell performs its specific tasks depending on its type (e.g., muscle cells contract, nerve cells transmit signals). It also synthesizes RNA and proteins that are necessary for its specific function. The cell is metabolically active, accumulating resources for DNA replication. The cell will proceed to the S phase if conditions are favorable.
b. S (Synthesis):
- Description: During the S phase, DNA replication occurs. Each chromosome is duplicated, ensuring that the cell has two full sets of genetic information. This step is crucial for ensuring that the daughter cells receive identical genetic material. The synthesis phase also involves the formation of sister chromatids, where each chromosome is made up of two identical chromatids joined at the centromere.
c. G2 (Gap 2):
- Description: This phase follows DNA replication and is primarily a period of growth and preparation for cell division. The cell continues to synthesize proteins and organelles necessary for mitosis. It also undergoes additional checks to ensure that the DNA is intact and that the cell is ready to divide. The cell essentially prepares for the physical division of its nucleus and cytoplasm in the next stage of the cell cycle.
d. M (Mitosis):
- Description: The M phase is the stage where the cell divides its duplicated DNA and cytoplasm into two identical daughter cells. Mitosis is the process that ensures each daughter cell gets an exact copy of the mother cell’s DNA. Mitosis consists of several sub-stages: prophase, metaphase, anaphase, and telophase. After mitosis, cytokinesis occurs, dividing the cell’s cytoplasm and creating two separate daughter cells.
2. Stages of Mitosis:
a. Prophase:
- Events: In prophase, the chromatin condenses into visible chromosomes, each consisting of two sister chromatids. The nuclear envelope begins to break down, and the mitotic spindle, made of microtubules, begins to form. The centrioles (in animal cells) move toward opposite poles of the cell, and the spindle fibers begin to attach to the centromere of each chromosome.
- Appearance: Chromosomes are visible as condensed structures, and the nuclear envelope is dissolving.
b. Metaphase:
- Events: The chromosomes align at the cell’s equator, known as the metaphase plate. Each sister chromatid is attached to spindle fibers from opposite poles. This alignment ensures that each daughter cell will receive an identical set of chromosomes.
- Appearance: Chromosomes are aligned in the middle of the cell along the metaphase plate.
c. Anaphase:
- Events: In anaphase, the sister chromatids are pulled apart toward opposite poles of the cell. This is done by the shortening of the spindle fibers attached to the centromeres. The separation ensures that each daughter cell will receive one copy of each chromosome.
- Appearance: The chromatids are now separate and moving toward opposite poles.
d. Telophase:
- Events: Telophase is the final stage of mitosis, where the separated chromatids (now individual chromosomes) begin to de-condense into chromatin. A new nuclear envelope forms around each set of chromosomes, creating two distinct nuclei. The spindle fibers dissolve, and the cell is nearly ready for division of the cytoplasm.
- Appearance: Two distinct nuclei are visible, and the chromatin is starting to spread out.
This explanation summarizes the cell cycle and mitosis, highlighting key processes at each stage.
