Q1. Explain how mitosis results in genetically identical cells, using the terms chromosome, chromatid, and chromatin.

Background

Topic: Mitosis and Genetic Continuity

This question tests your understanding of how the process of mitosis ensures that daughter cells are genetically identical to the parent cell, and how the structures of chromosomes, chromatids, and chromatin are involved in this process.

Key Terms:

• Chromosome: A structure made of DNA and proteins that contains genetic information.

• Chromatid: One of two identical halves of a duplicated chromosome.

• Chromatin: The complex of DNA and proteins that makes up chromosomes; it is less condensed during interphase.

Step-by-Step Guidance

1. Recall that before mitosis, DNA is replicated during the S phase of interphase, resulting in duplicated chromosomes composed of two sister chromatids.

2. Understand that during mitosis, the chromatin condenses to form visible chromosomes, each consisting of two identical sister chromatids joined at the centromere.

3. During the process of mitosis, the sister chromatids are separated and distributed to opposite poles of the cell.

4. Each chromatid is now considered an individual chromosome, and each daughter cell receives an identical set of chromosomes.

5. Think about how the structure of chromatin, chromosomes, and chromatids ensures that the genetic information is accurately copied and distributed.

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Q2. Describe the events of interphase and the M phase.

Background

Topic: Cell Cycle Phases

This question asks you to summarize the main events that occur during interphase (the period between cell divisions) and the M phase (mitosis and cytokinesis).

Key Terms:

• Interphase: The phase of the cell cycle when the cell grows, replicates its DNA, and prepares for division. It includes G1, S, and G2 phases.

• M phase: The phase of the cell cycle that includes mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).

Step-by-Step Guidance

1. Recall that interphase is divided into three subphases: G1 (cell growth), S (DNA synthesis/replication), and G2 (final preparations for division).

2. During G1, the cell grows and carries out normal metabolic functions.

3. In the S phase, the cell replicates its DNA, so each chromosome now consists of two sister chromatids.

4. During G2, the cell continues to grow and prepares for mitosis by producing proteins and organelles needed for cell division.

5. The M phase consists of mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis, where the cell physically divides into two daughter cells.

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Q3. Identify three checkpoints that control the cell cycle, and explain how they operate.

Background

Topic: Cell Cycle Regulation

This question tests your knowledge of the molecular mechanisms that regulate the cell cycle and ensure proper cell division.

Key Terms:

• Checkpoint: A control point in the cell cycle where stop and go-ahead signals regulate the cycle.

• G1 checkpoint: Checks for cell size, nutrients, growth factors, and DNA damage.

• G2 checkpoint: Checks for DNA replication completeness and DNA damage.

• M checkpoint (Spindle checkpoint): Checks for chromosome attachment to spindle fibers.

Step-by-Step Guidance

1. Recall that the cell cycle has three main checkpoints: G1, G2, and M.

2. At the G1 checkpoint, the cell decides whether to continue dividing or enter a resting state (G0) based on internal and external signals.

3. The G2 checkpoint ensures that DNA replication is complete and checks for DNA damage before the cell enters mitosis.

4. The M checkpoint (spindle checkpoint) ensures that all chromosomes are properly attached to the spindle apparatus before anaphase begins.

5. Think about how these checkpoints help prevent errors in cell division and maintain genetic stability.

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Q4. Label the indicated areas of the chromosome figure and define chromosome, chromatid, centromere, and chromatin.

Background

Topic: Chromosome Structure

This question helps you understand the physical structure of chromosomes and the terminology used to describe their parts.

Key Terms:

• Chromosome: A DNA molecule with part or all of the genetic material of an organism.

• Chromatid: Each of the two thread-like strands into which a chromosome divides during cell division.

• Centromere: The region of a chromosome where the two sister chromatids are joined.

• Chromatin: The material of which the chromosomes are composed; consists of protein, RNA, and DNA.

Step-by-Step Guidance

1. Identify the two thick strands in the image as sister chromatids, which are identical copies of a chromosome connected by a centromere.

2. The narrow region where the chromatids are joined is the centromere.

3. Remember that the entire structure is a duplicated chromosome, and each chromatid will become an individual chromosome after separation.

4. Chromatin refers to the less condensed form of DNA and proteins found during interphase.

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Q5. Summarize what occurs at the DNA level in each stage of the chromosome duplication and distribution diagram.

Background

Topic: Chromosome Duplication and Distribution

This question asks you to describe what happens to DNA during the stages of cell division, focusing on chromosome duplication and separation.

Key Terms:

• DNA replication: The process of copying DNA before cell division.

• Sister chromatids: Identical copies of a chromosome connected by a centromere.

• Chromosome separation: The process during mitosis when sister chromatids are pulled apart.

Step-by-Step Guidance

1. In the first stage, a single chromosome (one DNA molecule) is present in the cell.

2. During the second stage, DNA replication occurs, resulting in a duplicated chromosome with two sister chromatids (each with an identical DNA molecule).

3. In the third stage, the sister chromatids are separated into two new cells, each receiving one DNA molecule (now considered a chromosome).

4. Think about how this process ensures each daughter cell receives an identical set of genetic information.

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