Cell division and its control

Question 1

What is mitosis? Where does it occur?

Answer 1

daughter cell has the same number of genetically identical chromosomes as the parent cell.

Most cells

Question 2

What is meiosis?Where does it occur?

Answer 2

daughter cell has half the number of chromosomes as its parent.

Germ line cells- in ovaries and testies

Question 3

What holds single double helix of DNA

Answer 3

Chromatids

Question 4

Describe the 3 broad stages of cell division?

Answer 4

1. Interphase- DNA replication
2. mitotic (M phase)-Nucleus divides
3. Cytokenisis- Cytoplasm divides

Question 5

Describe the 3 main stages of inter phase and what happens at each stage

Answer 5

1. G1- Cell synthesis RNA, enzymes and proteins. No DNA synthesis.
   Check point at the end- determines if cell divides or enters G0
2. Synthesis- chromosomes are duplicated (short)
3. G2- Cell prepares for division. Increase in tubulin to make micro tubules to make mitotic spindles. Cell continues to grow

Question 6

What type of Cell enter G0?

Answer 6

Stem cells awaiting single to to re-enter the cell cyle

Post-mitotic cells no longer capable of mitosis

Question 7

List the 6 stages of mitosis in order

Answer 7

prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis.

Question 8

What occurs in prophase?

Answer 8

Nuclear chromatin condenses into chromosomes each consisting of two identical chromatids linked by centromer.
Mitotic spindle beings to form between centrioles

Question 9

What occurs in Prometaphase?

Answer 9

Chromosomes attach to microtubules by the kinetochore in the centromere. The centrioles move apart (in pairs) towards opposite ends forming microtubule organising centres.

Question 10

What occurs in Metaphase?

Answer 10

chromosomes become aligned in the centre of the mitotic spindle.

Question 11

What occurs in Anaphase?

Answer 11

chromatids seperate (opposite poles) to form the chromosomes of the daughter cells. The poles of the mitotic spindle move further apart.

Question 12

What occurs in Telophase?

Answer 12

separated chromosomes reach the poles of the mitotic spindle, which begins to disappear. A new nuclear membrane is formed around each daughter set of chromosomes and mitosis proper is complete.

Question 13

What occurs in Cytokinesis?

Answer 13

Cytoplasm of daughter cells divide.

A Contractile ring formed from actin and myosin pinches the cell until it splits (cleaves) into 2 daughter cells

Question 14

What is the consequence of errors during meiosis?

Answer 14

aneuploidy (abnormal number of chromosomes)

Question 15

What occurs in Meiosis- Prophase I?

Answer 15

Cell goes through an interphase period in which it grows, replicates its chromosomes.
Homologous pairs of chromosomes align and crossing over of chromosomal segments occurs.
Spindles form from microtubules.

Question 16

What causes Genetic Variation in Meiosis?

Answer 16

Recombination (homologous chromosomes) and independent assortment.
The chiasmata is the point of contact, between two chromatids of homologous chromosomes. At a chiasma, an exchange of genetic material occurs between both chromatids, - chromosomal crossover, does not occur in mitosis.

Question 17

What occurs in Meiosis – Metaphase I

Answer 17

Nuclear envelop dissolves
Pairs of chromosomes move to the equator of the cell. The homolougs chromosome facing each spindle pole (male or female) is random.

Question 18

What occurs in Meiosis – anaphase I?

Answer 18

Homologous chromosomes move to the opposite pole of each cell. Sister chromatids remain joined.

Question 19

What happens at Telophase I and Cytokinesis I ?

Answer 19

. Each daughter cell now has half the number of chromosomes but each chromosome consists of a pair of chromatids

Telophase 1- Spindle microtubles disappear. Nuclear membrane surrounds haploid set.
chromosomes uncoil back into chromatin. Sister chromatids remain attached.
Cytokensis occurs - completeing daughter cell creation
Cells may enter a period of rest known as interkinesis or interphase II. No DNA replication occurs during this stage.

Question 20

What happens at Meiosis II?

Answer 20

Cell division resembles a normal mitotic cell division in that the nuclear envelope reforms around each group of chromosomes. It differs in that it occurs without further DNA replication and the daughter cells have half the number of chromosomes of the parent.

Question 21

Use of cohesin in chromatid separation. What happens when it goes wrong?

Answer 21

Cohesin is a protein complex that regulates the separation of sister chromatids during cell division, either mitosis or meiosis. Cohesins hold sister chromatids together after DNA replication until anaphase when removal of cohesin leads to separation of sister chromatids.

Warsaw-Breakage Syndrome
(Cohesionpathy) develops

Question 22

List where all the cell cycle check point occure

Answer 22

1. G1-S
2. G2-M
3. Exit M

Question 23

What is assessed in the check point G1-S

Answer 23

The DNA of the cell is undamaged, cell organelles have been replicated and that the cell has sufficient organelles to divide

Question 24

What is assessed in the check point G2-M?

Answer 24

The DNA has been completely replicated correctly before the start of mitosis

Question 25

What is assessed in the check M

Answer 25

Have chromosomes attached to the mitotic spindle

Question 26

What triggers the Cell to move from one phase of the cell cycle to the other? State another function of this agent?

Answer 26

Cyclin which binds to cyclin-dependent protein kinases- phosphorylates proteins Acts at check points to interrupt progression

Question 27

Which tumour suppressor proteins detect DNA damage?

Answer 27

p53, p21 p53 blocks progression of cell cycle and Sythesizes P21 which inhibits CDK2

Question 28

State which cyclin regulates which part of the cell cycle

Answer 28

G1 phase-Cyclin D and CDK4 or S phase- Cyclin E-CDK2 Cyclin A-CDK2 activates DNA replication G2- Cyclin A-CDK1 Cyclin B-CDK1 takes cells into mitosis

Question 29

What is the function of the Retinoblastoma (Rb) protein? Describe how it does this

Answer 29

Prevents cells from from entering S. | When stimulated Cdk2 inactivates Rb thus releasing the E2F protein which activates S-phase entry

Question 30

Which cell activates S phase entery?

Answer 30

E2F

Question 31

Name 2 anti-microtuble agents and there mode of action

Answer 31

Vinca alkaloids -prevent the formation of the microtubules Taxanes- prevent microtubule disassembly

Question 32

what is the function of Anti-mitotics - Anti-microtubule agents

Answer 32

They prevent the cancer cells from completing mitosis. Cell cycle arrest occurs, which induces programmed cell death (apoptosis)

Question 33

Name 3 types of chemotherapy drugs and what they target

Answer 33

Anti-mitotic drugs- ant dividing cell Biologics- monoclonal antibodies Anti-hormonal drugs- block receptors on hormonal driven tumours