D2.1 Cell Division

Question 1

What is the dividing cell referred to?

Answer 1

Mother cell

Question 2

What are the new cells referred to?

Answer 2

Daughter cells

Question 3

Cytokinesis

Answer 3

The division of a cell’s cytoplasm to form two cells.

Question 4

How is cytokinesis carried out in plant cells?

Answer 4

1) Vesicles containing pectin line up in the middle of the cell.
2) Vesicles fuse together form a middle lamella.
2) Cellulose is added on either side to form a wall for each daughter cell.

Question 5

Cytokinesis in animal cells

Answer 5

1) Actin and myosin proteins adjacent to the cell membrane run parallel in a ring around the equator of the cell.
2) A and M exert tension to form a cleavage furrow.
3) The membrane is pulled inwards so it eventually splits the cell.

Question 6

What is an example of equal cytokinesis?

Answer 6

A human zygote dividing to form a two-cell embryo.

Question 7

What is are examples of unequal cytokinesis?

Answer 7

1) Oogenesis, where the small cell is a polar cell that soon dies.
2) Budding in yeast: The mother cell develops an outgrowth with little cytoplasm that then receives its own nucleus and separates.

Question 7

What happens to small cells produced by unequal cytokinesis?

Answer 7

They can grow and survive if they receive a nucleus and another organelle that cannot be assembled from cell components.

Question 8

What do u call cells without a nucleus?

Answer 8

Anucleate, like red blood cells (survive for approx 120 days).

Question 9

Why is nuclear division important?

Answer 9

• So each daughter cell can receive a nucleus and genetic information.
• Growth
• Reproduction
• Repair

Question 10

Why is DNA replication important before the start of meiosis and mitosis?

Answer 10

• The two daughter cells produced by mitosis will have the entire genome.
• Provides enough DNA for a mother cell to divide twice in meiosis.
• Provides enough DNA for recombination by the process of crossing over.

Question 11

How is DNA prepared for cell division?

Answer 11

1) DNA is elongated to chromatin.
2) DNA is replicated.
3) The 2 DNA molecules are condensed into structures called sister chromatins.

Question 12

How does DNA condensation to chromos take place?

Answer 12

• DNA double helix is wrapped around histone proteins.
• Resulting structures are added together.
• Supercoiling: 10,000um of DNA packed into 1ums of chromosome.

Question 12

Microtubules

Answer 12

Narrow tubular structures assembled by tubulin proteins.

Question 13

How are sister chromatids separated?

Answer 13

• More tubulins are added so that microtubules extend towards the cell’s equator.
• Kinetochores at the centromere remove tubulins to make microtubules pull the chromatids to the poles.

Question 14

Prophase

Answer 14

• Chromosomes are condensing.
• Microtubules grow from centrioles to form spindle shapes.
• Spindle microtubules extend from each pole to the equator.

Question 15

Metaphase

Answer 15

• Nuclear membrane has disintegrates.
• Chromosomes line up at the equator,
• Spindle microtubules attach to kinetochores, sister chromatids attached to separate poles.

Question 16

Anaphase

Answer 16

• Kinetochores shorten spindle microtubules, and the identical chromosomes are pulled to opposite poles.
• Each separated sister chromatid is now a chromosome.

Question 17

Telophase

Answer 17

• Chromosomes have reached the pole, spindle microtubules break down.
• Chromos uncoil and the cell goes through cytokinesis.

Question 18

Diplois Cell

Answer 18

A set of 23 homologous pairs of chromosomes.

Question 19

Haploid

Answer 19

23 chromosomes

Question 20

Prophase I

Answer 20

Homologous chromosomes pair up, spindle microtubules form, nuclear membrane breaks down.

Question 21

Metaphase I

Answer 21

• Chromosomes line up randomly at the equator.
• Spindle microtubules attach to a chromosome of the pair.

Question 22

Anaphase I

Answer 22

• Each chromosome is pulled to opposite poles of the cell.

Question 23

Prophase II

Answer 23

- New spindle microtubules form.

Question 24

Anaphase II

Answer 24

- Kinetochores pull chromatids to the poles. - Sister chromatids are non-identical because of exchange of alleles in crossing.

Question 25

Telophase II

Answer 25

- Chromosomes decondense inside, and the nuclear membrane forms. - 4 haploid cells are produced.

Question 26

Non-disjunction

Answer 26

When a pair of homologous chromosomes fails to separate in anaphase I.

Question 27

What causes Down syndrome?

Answer 27

Non-disjunction in pair 21 causes a zygote with a trisomy in chromosome 21.

Question 28

Bivariate

Answer 28

Pair of homologous chromosomes, one from each parent.

Question 29

What are the ways that meiosis produces genetic variation?

Answer 29

1) The random orientation of bivariates in metaphase I can produce many combinations when homologous pairs separate in anaphase I. 2) Chromosomes cross over in meiosis at random chiasma, which produces various combinations of alleles.

Question 30

Why is cell proliferation (repeated division of cells) needed in plants and animals?

Answer 30

1) Growth 2) Cell replacement for repair.

Question 31

What are the two main cycles the cell goes through?

Answer 31

Interphase and Mitosis

Question 32

What are the 3 phases of interphase?

Answer 32

G1: Cell synthesizes proteins and carries out its functions. S Phase: DNA is replicated G2: Cell grows, duplicates organelles, produces enzymes needed for division, etc..

Question 33

Cylins

Answer 33

Proteins are used to control progression through the checkpoints that separate, and their concentration rises and falls during the cell cycle.

Question 34

How do cyclins regulate teh cell cycle?

Answer 34

- They reach a threshold concentration. - Bind to kinase enzymes to activate them, kinases phosphorylate proteins. - Phosphorylated proteins perform tasks specific to the cell cycle.

Question 35

Mutations in what type of genes can cause tumour cells?

Answer 35

1) Proto-oncogenes 2) Suppressor genes that prevent uncontrolled cell division.

Question 36

Tumour

Answer 36

A mass of proliferating cells in which normal control of the cell cycle is lost.

Question 37

Primary tumours

Answer 37

Tumours that vary in their rate of growth.

Question 38

Benign Tumour

Answer 38

Ts that grow slowly and are not life-threatening.

Question 39

Malignant Tumour

Answer 39

Grow aggressively and may spread to other parts of the body.

Question 40

Metastasis

Answer 40

The spreading of cells to form secondary cells.

Question 41

Mitotic Index formula

Answer 41

(number of cells in mitosis)/Total number of cells