Week 17 / Protein Synthesis and Cell Cycle 2

Question 1

What happens during the G1 phase of interphase?

Answer 1

Answer:
- G1 is the interval between the mitotic phase and the S phase.
- The cell is metabolically active, replicating most organelles and cytosolic components (excluding DNA).
- Centrosome replication begins in G1.
- G1 lasts 8–10 hours in a 24-hour cell cycle.
- Cells in G1 for an extended time, potentially never dividing, enter the G0 phase.

Question 2

What happens during the S phase of interphase?

Answer 2

The S phase lasts about 8 hours and occurs between G1 and G2 phases.
DNA replication takes place, ensuring the two cells formed during division will have identical genetic material.
Flashcard 2: G2 Phase

Question 3

What happens during the G2 phase of interphase?

Answer 3

G2 is the interval between the S phase and the mitotic phase, lasting 4–6 hours.
Cell growth continues.
Enzymes and proteins required for division are synthesized.
Centrosome replication is completed.

Question 4

What happens to DNA during the S phase of interphase?

Answer 4

DNA partially uncoils, and the two strands separate where hydrogen bonds connect base pairs.

Each original DNA molecule is replicated, resulting in two identical DNA molecules.

Question 5

Q: What is Interphase?

Q: What structures are involved in Interphase?

Q: What is the function of the centrosome during Interphase?

Q: What happens to the chromatin during Interphase?

Q: What is the role of the nucleolus in Interphase?

Answer 5

A: Interphase is a phase in the cell cycle where the cell prepares for division, including growth and DNA replication.

A: Key structures include the centrosome, centrioles, pericentriolar material, nucleolus, nuclear envelope, chromatin, plasma membrane, and cytosol.

A: The centrosome organizes microtubules and is important for cell division.

A: Chromatin is in a relaxed state, allowing for DNA replication and gene expression.

A: The nucleolus is responsible for ribosome production and RNA synthesis.

Question 6

Q: What key events occur during prophase in mitosis?

Answer 6

A: During prophase, chromatin condenses into visible chromosomes, the mitotic spindle begins to form, the nuclear envelope breaks down, kinetochores form on centromeres, and centrosomes migrate to opposite poles of the cell.

Question 7

Question:
What happens during metaphase?

Answer 7

Answer:

Chromosomes align at the metaphase plate (the cell’s equatorial plane).

Each chromosome is attached to spindle fibers via its centromere.

The alignment ensures accurate separation of sister chromatids during the next phase.

Question 8

Question:
What happens during anaphase?

Answer 8

Answer:
Sister chromatids separate at the centromere, becoming individual chromosomes.

The chromosomes are pulled toward opposite poles of the cell by shortening spindle fibers.

This ensures each daughter cell will receive an identical set of chromosomes.

Question 9

Question:
What happens during telophase?

Answer 9

Chromosomes arrive at the opposite poles of the cell and begin to decondense into chromatin.

Nuclear envelopes reform around each set of chromosomes, creating two nuclei.

The spindle fibers break down and disappear.

Telophase marks the end of nuclear division, preceding cytokinesis.

Question 10

Question:
How is the cell cycle controlled by the checkpoint control system?

Flashcard 2: Go-Ahead Signal

Question:
What promotes cell growth and division at checkpoints?

Answer 10

Answer:
- Controlled by STOP and GO chemical signals at critical points.
- Signals ensure that key cellular processes have been completed correctly before the cycle proceeds.

Answer:
- Signals that promote growth and division include:

• Proteins (internal signals called “promoting factors”).
• External signals (called “growth factors”).
• Primary control mechanism: phosphorylation by kinase enzymes

Question 11

Question:
What roles do cyclins and CDKs play in the cell cycle?

Answer 11

Answer:
Cyclins and CDKs drive the cell from one phase to the next in the cell cycle.

Proper regulation of the cell cycle is crucial for life.

The genes for these regulatory proteins are highly conserved across evolution.

These genes are similar in organisms ranging from yeast to humans, including insects and plants.

Question 12

Question:
What is reproductive cell division, and how does it contribute to sexual reproduction?

Question:
What is the chromosome composition of gametes, and how is the diploid number restored?

Question:
What are the stages of meiosis?

Answer 12

Answer:
- Sexual reproduction involves the union of two gametes (fertilization), one from each parent.
- Meiosis, occurring in gonads (ovaries and testes), reduces the chromosome number by half to produce gametes.

Answer:
- Gametes are haploid (n) cells with a single set of 23 chromosomes.
- Fertilization restores the diploid (2n) number of chromosomes.

Answer:
- Meiosis occurs in two successive stages:
- Meiosis I
- Meiosis II

Question 13

Flashcard: Meiosis I

Question:
What happens during meiosis I?

Answer 13

Answer:
1. Prophase I
- Chromosomes condense, and homologous chromosomes pair up (synapsis).
- Crossing over occurs, exchanging genetic material between homologous chromosomes.
- Nuclear envelope breaks down, and spindle fibers form.

2. Metaphase I
   
   • Homologous chromosome pairs align at the metaphase plate.
   • Each pair is attached to spindle fibers from opposite poles.
3. Anaphase I
   
   • Homologous chromosomes are separated and pulled to opposite poles of the cell.
   • Sister chromatids remain attached at their centromeres.
4. Telophase I and Cytokinesis
   
   • Chromosomes reach opposite poles, and the nuclear envelope may reform briefly.
   • The cell divides into two haploid cells, each with half the original chromosome number (but still consisting of sister chromatids).

Question 14

Question:
What happens during meiosis II?

Answer 14

Prophase II

Chromosomes, each with two sister chromatids, condense.
The nuclear envelope breaks down, and spindle fibers form in each haploid cell.
Metaphase II

Chromosomes align along the metaphase plate in both haploid cells.
Spindle fibers attach to the centromeres of the chromosomes.
Anaphase II

The sister chromatids of each chromosome are pulled apart toward opposite poles.
Telophase II and Cytokinesis

Chromatids reach the poles, and new nuclear envelopes form around each set of chromosomes.
The cell divides, resulting in four haploid cells, each with a single set of chromosomes.
These four cells are genetically unique due to crossing over in meiosis I.

Question 15

Question 1:
How many divisions occur in mitosis and meiosis?

Question 2:
How many daughter cells are produced in mitosis and meiosis?

Question 3:
Are the daughter cells genetically identical in mitosis and meiosis?

Question 4:
What is the chromosome number of daughter cells in mitosis and meiosis?

Question 5:
Where do mitosis and meiosis occur?

Question 6:
When do mitosis and meiosis occur?

Question 7:
What are the roles of mitosis and meiosis?

Feature | Mitosis | Meiosis |

Answer 15

Answer:
- Mitosis: 1 division
- Meiosis: 2 divisions

Answer:
- Mitosis: 2 daughter cells
- Meiosis: 4 daughter cells

Answer:
- Mitosis: Yes, the daughter cells are genetically identical.
- Meiosis: No, the daughter cells are genetically different.

Answer:
- Mitosis: The chromosome number is the same as the parent.
- Meiosis: The chromosome number is half of the parent.

Answer:
- Mitosis: In somatic cells.
- Meiosis: In germ cells (ovaries and testes).

Answer:
- Mitosis: Throughout life.
- Meiosis: At sexual maturity.

Answer:
- Mitosis: Growth and repair.
- Meiosis: Sexual reproduction.

Question 16

Flashcard: Mitosis vs. Meiosis (Summary)

Question 1:
When does DNA replication occur in mitosis and meiosis?

Question 2:
How many divisions occur in mitosis and meiosis?

Question 3:
Does synapsis of homologous chromosomes occur in mitosis or meiosis?

Question 4:
What is the number of daughter cells and their genetic composition in mitosis and meiosis?

Question 5:
What is the role of mitosis and meiosis in the animal body?

Answer 16

• Mitosis: Occurs during interphase before nuclear division begins.
• Meiosis: Occurs once, during interphase before meiosis I begins.

Answer:
- Mitosis: One division, including prophase, metaphase, anaphase, and telophase.
- Meiosis: Two divisions, each including prophase, metaphase, anaphase, and telophase.

Answer:
- Mitosis: Does not occur.
- Meiosis: Synapsis occurs during prophase I, where homologous chromosomes join along their length, forming tetrads. This is associated with crossing over between nonsister chromatids.

Answer:
- Mitosis: Produces two daughter cells, each diploid (2n) and genetically identical to the parent cell.
- Meiosis: Produces four daughter cells, each haploid (n), containing half the chromosome number of the parent cell, and genetically non-identical to the parent and to each other.

Answer:
- Mitosis: Enables a multicellular adult to arise from a zygote and produces cells for growth and tissue repair.
- Meiosis: Produces gametes, reduces chromosome number by half, and introduces genetic variability among gametes.