cells alive 5- cell division

Question 1

how long does interphase usually take and what are the 3 stages?

Answer 1

• around 23 hours
• G1, S phase, G2

Question 2

how long is the M phase and what are the subdivisions?

Answer 2

• around 1 hour
  1. prophase
  2. prometaphase
  3. metaphase
  4. anaphase
  5. telophase
  6. cytokenesis

Question 3

what happens during interphase

Answer 3

• preparation for mitosis
• cell grows: doubling protein content
• organelles double in size or number
• during S phase DNA is synthesised
• centrosome replicates
  the two gaps which are G1 and G2 exist for he cell to confirm everything is ready for the next phase

Question 4

in the M phase, what happens during prophase?

Answer 4

1. chromosomes condense
2. mitotic spindle forms
3. centrosomes move apart
4. protein complex (kinetochore) forms at centromere of the chromosome ( bit where 2 arms meet)

Question 5

in the m phase, what happens during prometaphase?

Answer 5

1. nuclear envelope breaks downs which allws microtubules access to the chromosomes
2. chromosomes attach o the microtubule via kinetochore complex

Question 6

in the M phase, what happens during metaphase?

Answer 6

1. chromosomes align at the equator
2. sister chromatids attach to opposite poles by kinetochore microtubules

Question 7

during the M phase, what happens during anaphase?

Answer 7

1. cohesive link between sister chromatids is released
2. kinetochore microtubules shorten
3. centrosomes move apart

results in sister chromatids simultaneously pulled to opposite poles

Question 8

during M phase, what happens during telophase?

Answer 8

1. daughter chromosomes reach the poles
2. new nuclear envelope forms from fragments attached to individual chromosomes. therefore 2 nuclei
3. contractile ring begins to form around the equator

Question 9

in the M phase, what happens during cytokinesis?

Answer 9

1. the ring contracts partitioning cytoplasm into 2 daughter cells
   each cell contains
   - one nucleus
   - one centrosome
   share of all organelles
2. DNA decondenses and the cells return to resting interphase (G1)

Question 10

which step is the end of mitosis?

Answer 10

telophase

Question 11

what role does the cytoskeleton play in the cell cycle?

Answer 11

• increased instability in the cytoskeleton
• motor proteins move various components around
• nuclear lamina ( intermediate filaments) needs to disassemble
• actin cytoskeleton involved in ring interaction during cytokinesis
• microtubules’ role in cellular rearrangements

Question 12

specifically to stages what does the cytoskeleton do?

Answer 12

• kinetochore microtubules attach to chromosomes, prometaphase they grow and shrink as they find the target
• in metaphase motor proteins pull chromosomes until they are aligned
• in anaphase kinetochore microtubules shorten and motor proteins move the chromatids towards the centrosome

Question 13

3 checkpoints in the cell cycle, explain

Answer 13

• Restriction point: end of G1: MOST IMPORTANT
• environmental check
• DNA damage check
• turns on genes that promote entry into mitosis
• activates transcription factor Myc
• triggers intracellular signaling pathway
• G2-M transition:
• environment check
• DNA damage check
• Replication complete
• Meta-anaphase transition:
• checks chromosomes are attached

Question 14

clinical relevance of the cell cycle?

Answer 14

uncontrolled cell division leads to cancer
- mutation in signaling pathways that override restriction point
- mutation in checkpoint regulators
- tumour suppressors or oncogenes

Question 15

name the cell division cycle genes

Answer 15

• cyclin-dependent kinases (CDK’s)
• cyclin: bind and activate CDKs
• CAK: CDK activating kinase: activate cyclin- CKD complex

Question 16

haploid number

Answer 16

one copy of each chromsome

Question 17

diploid number

Answer 17

2 copies of each chromosome (except sex chromosomes in males)

Question 18

somatic cells

Answer 18

normal cells of the body, contain diploid number of chromosomes e.g 46 in humans

Question 19

reproductive cells

Answer 19

• gametes (sperm and eggs)
• contains haploid number of chromomes e.g 23 in humans
• formed by meiosis

Question 20

what does meiosis produce?

Answer 20

haploid eggs and sperm

Question 21

what are the 2 stages of meiosis?

Answer 21

interphase I

prophase I

Question 22

what happens during interphase I in meiosis?

Answer 22

DNA replicates resulting in pairs of chromatids

Question 23

what happens in prophase I of meiosis?

Answer 23

• leptotene: chromosomes condense
• zygotene: homologous chromosome align and linked by synaptonemal complexes (synapsis)
• pachytene: pairs of chromosomes coli; crossing over (recombination)
• diplotene: synaptonemal complexes break down, pairs of chromosomes linked ay crossover points (chiasmata)
• diakinesis: chromosomal condensation reaches maximum
• metaphase I, anaphase I and telophase I as for mitosis but 23 pairs not 46
• meoisis II: without further DNA replication another round of division occurs

Question 24

what is reduction division?

Answer 24

cell goes from diploid to haploid

Question 25

4 differences of meiosis and mitosis

Answer 25

meiosis: DNA replicates then cell divides twice
mitosis: DNA replicates then cell divides once

products:
mieosis: 4 cells with half the number of chromosomes of the parent’s cell
mitosis: two cells with the number of the same chromosome as the parents

meiosis: cells are unique
mitosis: cells are identical

roles
meiosis: products are the gametes required for sexual reproduction
mitosis: increases the number of cells in a multicellular organism