Cell and Nuclear Division

Question 1

How are new cells generated in living organisms?

Answer 1

Cell division.
Parent cell/mother cell divides to produce two daughter cells.
Three stages: DNA replication, Nuclear Division and Cytokinesis

Question 2

What is cytokinesis?

Answer 2

Splitting of cytoplasm in parent cell between daughter cells, following the division of the nucleus

Question 3

What is equal cytokinesis

Answer 3

Cytokinesis that produces two identical daughter cells, each receiving:
-Full copy of parent cell’s DNA
-Some of the essential organelles
- At least one mitochondrian (chloroplast in plants)

Question 4

What is unequal cytokinesis?

Answer 4

Cytokinesis in which the cytoplasm is divided unequally -> New cell evolves as an outgrowth
E.g. oogenesis and budding

Question 5

What is the difference between nuclear division during mitosis and meiosis?

Answer 5

Mitosis:
- Single nuclear division.
- Produces two genetically identical daughter cells
- Same number of chromosomes as the parent cell
- E.g cell proliferation
Meiosis:
- Two nuclear divisions
- Produces four genetically distinct daughter cells.
- Half the number of chromosomes as the
parent cell.
- E.g sex cells

Question 6

Why does DNA replication take place before mitosis?

Answer 6

A complete copy of the cell’s DNA needs to be made.

Question 7

Describe how chromosomes are condensed

Answer 7

DNA is wrapped around histone proteins, becoming chromatin.
It is coiled and then supercoiled, the coils stacking on top of each other to form a compact pair of chromatids.

Question 8

How do chromosomes move?

Answer 8

Microtubuli from the centrosome attach to the kinetochore protein at the centromere of the chromosome
Motor proteins coordinate movement -> walk on the overlapping microtubules

Question 9

What are the phases of mitosis?

Answer 9

Prophase, metaphase, anaphase, telophase

Question 10

What occurs during prophase?

Answer 10

Chromatin fibres become more tightly coiled => chromosomes
Nuclear membrane breaks down
Paired centrosomes move to opposite poles of the cell and produce microtubule spindle fibres.

Question 11

What occurs during metaphase?

Answer 11

Chromosomes line up along the centre of the cell
Kinetochores attach to the centromere.

Question 12

What occurs during anaphase?

Answer 12

The sister chromatids seperate.
Chromosomes are pulled by spindle fibres to opposite poles of the cell

Question 13

What occurs during telophase

Answer 13

Chromosomes arrive at the poles.
New nuclear membranes reform around each set of chromosomes
Chromosomes decondense into chromatin.
Microtubule spindle fibres dissolve.

Question 14

What do the phrases ‘diploid’ and ‘haploid’ mean?

Answer 14

Diploid: cell has two sets of chromosomes
Haploid: cell has a single set of chromosomes

Question 15

What does meiosis result in?

Answer 15

Four haploid nuclei from one diploid nucleus

Question 16

Outline the first four steps of meiosis

Answer 16

Prophase I:
- The homologous chromosomes associate with each other to form bivalents.
- Crossing over between non-sister chromatids -> recombinants formed
Metaphase I:
- The homologous pairs line up at the equator.
- Random orientation occurs.
- The nuclear membrane disintergrates
Anaphase I:
- Homologous pairs are seperated and pulled to opposite poles.
- Redution division
Telophase I:
- Nuclei are haploid.
- Cytoplasm begins to divide. New nuclear membranes.
- Chromosomes decondense

Question 17

Outline the last 4 steps of meiosis

Answer 17

Prophase II:
- Meiotic spindle fibres are produced
Metaphase II:
- Pairs of sister chromatids line up at the equator.
- Spindle fibres form, attach to centromeres
Anaphase II:
- Spindle fibres contract => centromeres are split
- Sister chromatids seperated.
- Chromosomes are pulled to opposite poles.
Telophase II:
- Four new haploid membranes are formed.
- Nuclear membranes reform.
- Chromosomes decondense. Cytokinesis begin

Question 18

How does meiosis create genetic variation?

Answer 18

Random orientation of bivalents during metaphase I
Crossing over during prophase I

Question 19

Why does cells proliferate? Give an example of cell proliferation

Answer 19

Growth, cell replacement, tissue repair.
Skin must continue to divide by mitosis to replace dead cells to heal a wound

Question 20

What are the phases of the cell cycle

Answer 20

Interphase (including G1, S and G2), mitosis, cytokinesis

Question 21

What occurs during interphase?

Answer 21

Cell growth, this is a metabolically active period.
G1: cell grows, intake of nutrients, proteins are formed
S: DNA is synthesised
G2: number of mitochondria and chloroplasts increase

Question 22

What are cyclins?

Answer 22

Regulatory proteins that work with CDKs to control the cell cycle.

Question 23

What is the function of cyclins?

Answer 23

When binded to CDKs they act as enzymes and cause the cell to go from one phase to the next.
A specific level of cyclins is required to pass each checkpoint in the cycle.
The number of cyclins increase and decrease during the cell cycle

Question 24

What are the consequences of mutations in genes that control the cell cycle

Answer 24

Mutations in proto-oncogenes convert them to oncogenes which actively promote cell proliferation

Mutations in tumoursuppressor genes, result in uncontrolled cell division

Question 25

Name some different types of tumours and state whether they do or do not cause cancer

Answer 25

Benign tumour: does not spread to other parts of the body
Malignant tumour: spreads and invades nearby normal tissues, developing secondary tumours. Cancerous.
Primary tumour: cancer growing at the original site
Secondary tumour: copies of the primary tumour