Week 17 / Protein Synthesis and Cell Cycle 2

Question 1

What is the G1 phase ?

Answer 1

• G1 is the interval between the mitotic phase and the S phase.

Question 2

What happens during the G1 phase of interphase?

Answer 2

• 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 3

What happens during the S phase of interphase?

Answer 3

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 4

What happens during the G2 phase of interphase?

Answer 4

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 5

What happens to DNA during the S phase of interphase?

Answer 5

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 6

What is Interphase?

Answer 6

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

Question 7

What structures are involved in Interphase? [8]

Answer 7

the centrosome,
centrioles,
pericentriolar material,
nucleolus,
nuclear envelope,
chromatin,
plasma membrane,
cytosol.

Question 8

What is the function of the centrosome during Interphase?

Answer 8

The centrosome organizes microtubules and is important for cell division.

Question 9

What happens to the chromatin during Interphase?

Answer 9

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

Question 10

What is the role of the nucleolus in Interphase?

Answer 10

The nucleolus is responsible for ribosome production and RNA synthesis.

Question 11

What key events occur during prophase in mitosis?

Answer 11

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 12

What happens during metaphase?

Answer 12

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 13

What happens during anaphase?

Answer 13

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 14

What happens during telophase?

Answer 14

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 15

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

Answer 15

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

Question 16

What promotes cell growth and division at checkpoints?

Answer 16

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

Question 17

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

Answer 17

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 18

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

Answer 18

• 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.

Question 19

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

Answer 19

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

Question 20

What are the stages of meiosis?

Answer 20

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

Question 21

What happens during meiosis I?

Answer 21

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 22

What happens during meiosis II?

Answer 22

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 23

How many divisions occur in mitosis and meiosis?

Answer 23

• Mitosis: 1 division
• Meiosis: 2 divisions

Question 24

How many daughter cells are produced in mitosis and meiosis?

Answer 24

• Mitosis: 2 daughter cells
• Meiosis: 4 daughter cells

Question 25

Are the daughter cells genetically identical in mitosis and meiosis?

Answer 25

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

Question 26

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

Answer 26

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

Question 27

Where do mitosis and meiosis occur?

Answer 27

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

Question 28

When do mitosis and meiosis occur?

Answer 28

• Mitosis: Throughout life.
• Meiosis: At sexual maturity.

Question 29

What are the roles of mitosis and meiosis?

Answer 29

• Mitosis: Growth and repair.
• Meiosis: Sexual reproduction.

Question 30

When does DNA replication occur in mitosis and meiosis?

Answer 30

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

Question 31

How many divisions occur in mitosis and meiosis?

Answer 31

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

Question 32

Does synapsis of homologous chromosomes occur in mitosis or meiosis?

Answer 32

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.

Question 33

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

Answer 33

• 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.

Question 34

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

Answer 34

• 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.