cell cycle review
1. what is responsible for moving chromosomes during mitosis?

2. in what phase does a cell spend most of its life?

3. what does each phase of mitosis look like?

4. what happens during each of the phases?

5. what are the four phases of mitosis (from first to last)?

6. what are chromatids? how do they differ from chromosomes?

7. what are chromosomes made of? where are they found?

8. what is a centromere?

9. what are the five parts of the cell cycle?

10. how many chromosomes are in a human body cell?

Question

cell cycle review
1. what is responsible for moving chromosomes during mitosis?

2. in what phase does a cell spend most of its life?

3. what does each phase of mitosis look like?

4. what happens during each of the phases?

5. what are the four phases of mitosis (from first to last)?

6. what are chromatids? how do they differ from chromosomes?

7. what are chromosomes made of? where are they found?

8. what is a centromere?

9. what are the five parts of the cell cycle?

10. how many chromosomes are in a human body cell?

Accepted Answer

To answer these cell cycle - related questions, we'll go through each one:

### Question 1
#### Brief Explanations:
Spindle fibers, which are made of microtubules, attach to the chromosomes at the centromeres. During mitosis, these spindle fibers contract and pull the chromosomes to the opposite poles of the cell.
#### Answer:
Spindle fibers (composed of microtubules) are responsible for moving chromosomes during mitosis.

### Question 2
#### Brief Explanations:
The interphase is the phase where the cell grows, replicates its DNA, and prepares for cell division. A cell spends about 90% of its life cycle in interphase. It has three sub - phases: G₁ (growth and normal cell function), S (DNA synthesis), and G₂ (preparation for mitosis).
#### Answer:
A cell spends most of its life in interphase.

### Question 3
#### Brief Explanations:
- **Prophase**: The chromatin condenses into visible chromosomes. The nuclear envelope breaks down, and the spindle apparatus starts to form. The centrioles (in animal cells) move to opposite poles.
- **Metaphase**: The chromosomes line up along the equator (metaphase plate) of the cell. The spindle fibers are fully formed and attached to the centromeres of each chromosome.
- **Anaphase**: The sister chromatids are pulled apart by the shortening of the spindle fibers. The separated chromatids (now called daughter chromosomes) move towards opposite poles of the cell.
- **Telophase**: The chromosomes reach the poles and start to de - condense back into chromatin. The nuclear envelope reforms around each set of chromosomes, and the spindle apparatus breaks down.
#### Answer:
- Prophase: Chromatin → chromosomes, nuclear envelope breaks, spindle forms.
- Metaphase: Chromosomes line up at metaphase plate.
- Anaphase: Sister chromatids separate, move to poles.
- Telophase: Chromosomes de - condense, nuclear envelope reforms.

### Question 4
#### Brief Explanations:
- **Prophase**: Chromatin condenses into chromosomes. The nuclear membrane dissolves. The mitotic spindle begins to assemble as centrioles (in animal cells) move to opposite ends of the cell.
- **Metaphase**: The spindle fibers attach to the centromeres of the chromosomes. The chromosomes align at the cell's equatorial plane (metaphase plate) so that they can be evenly distributed to the daughter cells.
- **Anaphase**: The centromeres split, and the sister chromatids are pulled apart by the spindle fibers. Each chromatid is now considered a separate chromosome and moves towards opposite poles of the cell.
- **Interphase (not mitosis, but part of cell cycle)**: In G₁, the cell grows and performs normal metabolic functions. In S phase, DNA replication occurs, duplicating the genetic material. In G₂, the cell prepares for mitosis by synthesizing proteins and organelles needed for cell division.
- **Telophase**: The chromosomes reach the poles and start to uncoil. A new nuclear envelope forms around each group of chromosomes. The mitotic spindle disassembles. In cytokinesis (which often starts in telophase), the cytoplasm divides, resulting in two daughter cells.
#### Answer:
- Prophase: Chromatin → chromosomes, nuclear envelope breakdown, spindle formation.
- Metaphase: Chromosomes align at metaphase plate, spindle attachment.
- Anaphase: Sister chromatids separate, move to poles.
- Telophase: Chromosomes de - condense, nuclear envelope reforms, spindle breakdown.
- Interphase (G₁: growth/function; S: DNA replication; G₂: prep for mitosis).
- Cytokinesis (during/after telophase): Cytoplasm divides.

### Question 5
#### Brief Explanations:
Mitosis is the process of nuclear division in eukaryotic cells. The four phases, in order, are prophase, metaphase, anaphase, and telophase. Prophase is the first phase where the cell starts to prepare for chromosome separation. Then in metaphase, the chromosomes align. Anaphase is when the chromatids are pulled apart, and telophase is the final phase of nuclear division.
#### Answer:
The four phases of mitosis (from first to last) are Prophase, Metaphase, Anaphase, Telophase (abbreviated as PMAT).

### Question 6
#### Brief Explanations:
- **Chromatids**: A chromatid is one of the two identical copies of a chromosome that are joined together at the centromere. They are formed during the S phase of interphase when DNA replication occurs.
- **Difference from chromosomes**: A chromosome can consist of one (after separation in anaphase) or two chromatids (before anaphase during mitosis). When a chromosome has two chromatids, it is in a duplicated state. A single chromatid is a half of the duplicated chromosome structure, and when the centromere splits, each chromatid becomes an individual chromosome.
#### Answer:
- Chromatids: One of two identical copies of a chromosome, formed in S phase.
- Difference: A chromosome can have 1 or 2 chromatids; chromatids are part of a duplicated chromosome, and separate to become chromosomes in anaphase.

### Question 7
#### Brief Explanations:
- **Composition of chromosomes**: Chromosomes are made up of DNA (deoxyribonucleic acid) and proteins called histones. The DNA is tightly coiled around the histones to form a compact structure that can be easily managed during cell division.
- **Location of chromosomes**: In eukaryotic cells, chromosomes are found within the nucleus. The nucleus is a membrane - bound organelle that houses the genetic material of the cell.
#### Answer:
- Chromosomes are made of DNA and histone proteins.
- They are found in the nucleus of eukaryotic cells.

### Question 8
#### Brief Explanations:
A centromere is a specialized region of a chromosome. It is the point where the two sister chromatids are attached to each other. The spindle fibers attach to the centromere during mitosis, and it plays a crucial role in the separation of the sister chromatids during anaphase.
#### Answer:
A centromere is the region of a chromosome where sister chromatids are attached, and where spindle fibers attach during mitosis.

### Question 9
#### Brief Explanations:
The cell cycle is the series of events that a cell goes through as it grows and divides. The five main parts are:
1. **G₁ (Gap 1)**: The cell grows in size, synthesizes proteins, and performs its normal cellular functions.
2. **S (Synthesis)**: The cell replicates its DNA, so that each chromosome is duplicated.
3. **G₂ (Gap 2)**: The cell continues to grow and prepares for mitosis by synthesizing the necessary proteins and organelles.
4. **M (Mitosis)**: This is the phase of nuclear division, which includes prophase, metaphase, anaphase, and telophase.
5. **C (Cytokinesis)**: The cytoplasm of the cell divides, resulting in two daughter cells.
#### Answer:
The five parts of the cell cycle are G₁ (Gap 1), S (Synthesis), G₂ (Gap 2), M (Mitosis), and C (Cytokinesis).

### Question 10
#### Brief Explanations:
Human body cells (somatic cells) are diploid, meaning they have two sets of chromosomes. Each set contains 23 chromosomes, so in total, a human body cell has 23 pairs of chromosomes, which is 46 chromosomes.
#### Answer:
There are 46 chromosomes in a human body cell (23 pairs).

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