Cell cycle!

Question 1

What is interphase?

Answer 1

When the cell prepares for cell division whilst also carrying out its normal cellular function.

Question 2

What is G1?

Answer 2

The cell produces proteins needed to replicate organelles and also replicates the organelles. Produces enzymes needed for DNA replication in S phase.

Question 3

What is checked at the G1 checkpoint?

Answer 3

The DNA is checked for errors before it is replicated, the growth factors are checked, the cell checks that all the chemicals needed for replication are available.

Question 4

What happens in the S phase?

Answer 4

In the synthesis phase DNA is replicated. This is a very quick stage as in this stage the DNA bases are highly susceptible to mutagenic agents.

Question 5

What is the centrosome?

Answer 5

Location in the cytoplasm of animal cells where centrioles are usually found.

Question 6

What is G0?

Answer 6

It is continuously ongoing and is when a cell either permanently or temporarily leaves the cell cycle. This means that the cell continues to carry out its regular processes but is no longer preparing for cell division.

Question 7

What are the reasons for cells moving into G0?

Answer 7

1. Apoptosis: Programmed cell death.
2. Differentiation.
3. Senescence: Cell is no longer working very effectively so is slowly moving towards apoptosis.

Question 8

What is the biochemical process that takes place at a checkpoint?

Answer 8

1. The p53 gene AKA. the tumour suppressor gene checks what needs to be checked at the checkpoint.
2. If there is an error the cell cycle will be halted to prevent uncontrolled cell division.
3. If there are no errors the p53 gene will stimulate the cyclins to bind to the cyclin dependent kinase enzyme which will allow the cell to move into the next stage.

Question 9

What happens in the G2 phase?

Answer 9

The cell continues to grow and increases its energy stores.

Question 10

What are the purposes of checkpoints?

Answer 10

1. To ensure DNA has been replicated correctly.
2. To detect and stop uncontrolled cell division.
3. To ensure DNA has only been replicated once.
4. To ensure the cell cycle is sequential.

Question 11

What happens at the G2 checkpoint?

Answer 11

The replicated DNA is checked for errors and the size of the cell is checked.

Question 12

What is a chromosome?

Answer 12

A thread-like structure in the nucleus of an animal or plant cell made of:
1. DNA
2. DNA-histone complex
3. Chromatin
4. Chromatids attached at a centromere.

Question 13

How are chromosomes arranged?

Answer 13

Chromosomes are arranged in pairs so that there are two homologous chromosomes, one maternal and one paternal, that are the same gene but may be alleles of one another. The first 22 chromosome pairs are autosomes and are the same in both men and women but the 23rd pair is the sex-determining pair.

Question 14

What is cytokinesis?

Answer 14

The cytoplasm of the cell divides forming two cells.

Question 15

What processes cause the daughter cells in meiosis to be genetically different?

Answer 15

1. Recombination
2. Independent segregation

Question 16

What is individual segregation or random assortment?

Answer 16

Random assortment is when
Homologous chromosomes line up at the equator of the cell.
However, whether the maternal or paternal chromosome is on the left or right is random meaning which chromosomes appear in daughter cells is also random.

Question 17

What is crossing over?

Answer 17

Recombination is when in
1. Prophase I chromosomes condense and pair up.
2. Chromatids of each chromosome twist around one another, forming a chiasmata.
3. When the chromosomes are separated during anaphase I, the chromatids break at the chiasmata and then reconnect to the chromatids from the homologous chromosome.

Question 18

What are the key functions in mitosis and meiosis?

Answer 18

Mitosis: Growth and repair
Meiosis: Producing gametes

Question 19

What are the types of reproduction in mitosis and meiosis?

Answer 19

Mitosis: Asexual
Meiosis: Sexual

Question 20

What is the genetic variation in mitosis and meiosis?

Answer 20

Mitosis: Genetically identical daughter cells
Meiosis: Genetically varied daughter cells

Question 21

What is separated in mitosis and meiosis?

Answer 21

Mitosis:
anaphase -> Replicated chromosomes
Meiosis:
anaphase I -> homologous chromosome pairs (reduces chromosome number by half)
anaphase II -> chromosomes

Question 22

What are the daughter cells in mitosis and meiosis?

Answer 22

Mitosis: diploid
Meiosis: haploid

Question 23

What are the differences between diploid and haploid cells?

Answer 23

Diploid:
1. 2 sets of chromosomes
2. Body cells
Haploid:
1. 1 set of chromosomes
2. Gametes

Question 24

What is the first stage of mitosis?

Answer 24

PROPHASE:
1. Nuclear envelope disappears/ disintegrates.
2. Nucleolus disappears.
3. Chromosomes condense.
4. Centrioles migrate to opposite poles of the cells and start forming spindle fibres.

Question 25

What is the second stage of mitosis?

Answer 25

METAPHASE: 1. Chromosomes line up at the equator of the cell. 2. Spindle fibres attach to chromosomes by their centromeres.

Question 26

What is the third stage of mitosis?

Answer 26

ANAPHASE: The spindle fibres contract pulling sister chromatids towards opposite poles of the cell by their centromere.

Question 27

What is the fourth stage of mitosis?

Answer 27

TELOPHASE: 1. Chromosomes reach opposite poles of the cells and uncoil to become long and thin chromosomes. 2. Nucleolus reappears. 3. Nuclear envelope reforms.

Question 28

What are the two parts of meiosis?

Answer 28

1. Meiosis I -> Homologous chromosomes are separated. 2. Meiosis II -> Chromatids are separated.

Question 29

What happens in meiosis I?

Answer 29

PROPHASE I: Chromosomes condense, nuclear envelope disintegrates, nucleolus disappears, centrioles migrate to opposite poles of the cells. METAPHASE I: Homologous pairs line up at the equator of the cell and spindle fibres attach to the chromosomes by their centromere. ANAPHASE I: Chromosomes are pulled to opposite poles of the cell by their centromere. TELOPHASE I: Chromosomes uncoil to form long, thin chromosomes and the nucleolus reappears, nuclear envelope reforms and cytokinesis occurs

Question 30

What happens in meiosis II?

Answer 30

1. Prophase II: - The chromosomes condense and are now visible under a microscope. - Centrioles migrate to opposite poles of the cell where each centriole starts forming spindle fibres. - The nucleolus disappears and the nuclear envelope starts to break down. 2. Metaphase II -The chromosomes line up at the equator of the cell (so in humans, 23 chromosomes line up). -Each chromosome attaches to the spindle by their centromere. 3. Anaphase II -The centromeres divide and separate each pair of chromatids. -The spindle fibres contract and shorten to pull the chromatids to opposite poles of the cell. 4.Telophase II: -The chromatids reach the opposite poles of the cell where they uncoil to become long and thin again. -A nuclear envelope forms around each set of chromosomes to form two nuclei and the nucleolus starts to reform. -The cytoplasm divides (cytokinesis) and 4 cells are produced.