Topic 10: cell cycle

Question 1

Define cell division + it’s role

Answer 1

• In unicellular = reproduction = binary fission
• In multicellular = growth + development + repair damage

Question 2

Describe the 2 cell division processes

Answer 2

MITOSIS:
- Produces somatic cells = diploids
- Conserves chromosome number
- 2 genetically identical cells to parent cell
MEIOSIS:
- Produces gametes = haploids
- Reduces chromosome number in half
- Produced in gonads

Question 3

Define fertilization

Answer 3

• Male + female gametes fuse = zygote = complete set of chromosomes = diploid

Question 4

Define cancer

Answer 4

• Abnormal growth = proliferates uncontrollably = metastasize

Question 5

Define cell cycle

Answer 5

• Functional process cell goes through = divided into 2 identical daughter cells

Question 6

What are the phases of the cell cycle?

Answer 6

1) Interphase = G1/S/G2
2) Mitotic phase = mitosis + cytokinesis

Question 7

Describe G0 phase

Answer 7

• Resting phase = non-dividing cells
• Differentiated cells = enter G0 > G1 due to growth factors
• Cells exit G1 > G0 = to differentiate

Question 8

What causes cell cycle control?

Answer 8

1) Extracellular signals = presence of growth factors
2) Intracellular signals = cell size

Question 9

Cell types + cell division potential

Answer 9

1) Post-mitotic cells:
- Terminally differentiated = cannot replicate
- Permanently in G0 phase
- E.g. neural + cardiac muscle + RBC
2) Cells dividing upon stimulation:
- Most body cells only divide by growth factors
- E.g. lymphocytes when antigenic presentation
3) Cells with high mitotic activity:
- E.g. germ + stem + epithelial cells

Question 10

Define interphase

Answer 10

• Period between cell divisions
• Largest phase of cell cycle
• Prepares cell for division OR decides if needs to proceed with division
• G1/S/G2

Question 11

Define G1 phase

Answer 11

• Prepare for DNA replication
• Protein synthesis + organelle production
• Duration = 5-6 hrs

Question 12

Define S phase

Answer 12

• DNA replication
• Duration = 10-12 hrs

Question 13

Define G2 phase

Answer 13

• Prepare for cell division
• Protein synthesis + organelle production
• Duration = 4-6 hrs

Question 14

Describe eukaryotic chromosomes

Answer 14

• Chromatin = complex of DNA + proteins = histones
• Each chromosome = 100-1000s genes
• Cells DNA = about 2m long

Question 15

2 types of cells + chromosomal content

Answer 15

SOMATIC:
- Diploid = 2n
- 2 sets of 23 chromosomes = total 46 = 23 pairs
- Each homologous pair = 1 paternal + 1 maternal
GAMETES:
- Haploid = n
- Only 1 set of 23 chromosomes = total
- Either maternal/paternal

Question 16

Define homologous chromosome

Answer 16

• Carry same genes at same position

Question 17

Describe the distribution of chromosomes during cell cycle

Answer 17

• Interphase = not condensed
• G1 = each chromosome = 1 chromatid
• S = DNA replicated
• G2 = duplicated chromosome = 2 sister chromatids joined at centromere
• Mitosis = chromosomes condense + sister chromatids seperate

Question 18

5 Phases of mitosis

Answer 18

1) Prophase
2) Prometaphase
3) Metaphase
4) Anaphase
5) Telophase

Question 19

Describe prophase

Answer 19

• Chromatin = condenses into visible chromosomes
• Nucleoli disappear + nuclear membrane = begins degrading
• Mitotic spindle begins to form

Question 20

Describe prometaphase

Answer 20

• Nuclear envelope fragments
• Microtubules from centrosome bind to chromosome
• Chromosomes = more condensed

Question 21

Describe metaphase

Answer 21

• Centrosomes = opposite poles
• Chromosomes aligned on metaphase plate = by polymerisation/depolymerisation of kinetochore
• If chromosomes not aligned properly = cell cycle arrest signal

Question 22

Describe anaphase

Answer 22

• Sister chromatids pulled to opposite poles = due to inactivation of centromere proteins hl=olding together chromatids
• By end of anaphase = each pole = equivalent chromosomes

Question 23

Describe telophase

Answer 23

• Nuclear envelope reforms
• Nucleoli reappears
• 2 daughter nuclei form
• Chromosomes decondense
• Mitosis completed

Question 24

Describe cytokinesis in animal cells

Answer 24

• Forms cleavage furrow
• Contractile ring formation = ring of actin + myosin contracts = complete separation

Question 25

Describe cytokinesis in plant cells

Answer 25

- Vesicles with cell wall material = at metaphase plate - Cell plate formation = vesicle fusion - Cell plate elongates = fuses with parental cell wall = creates 2 seperations

Question 26

Describe mitotic spindle formation + kinetochore function

Answer 26

- Begins to form by polymerization of microtubules at centrosome - Kinetochores = protein structure at centromere of chromosome - Mitotic spindle attaches at kinetochores - Kinetochore moves chromosomes toward metaphase plate

Question 27

Describe the 3 types of mitotic spindles

Answer 27

1) Astral = radial star-like structure around centrosome - Function = positioning of spindle 2) Kinetochore = join centrosome + centromere - Function = chromosomal movement 3) Polar = start from centrosome BUT don't attach - Function = maintain integrity of spindle

Question 28

Describe nuclear envelope/organelle degradation

Answer 28

- Lamin Proteins = intermediate filaments that make up the nuclear lamina - Enzymes phosphorylate lamins = nuclear lamina to break down = disassembly of nuclear envelope - NE + ER + Golgi break apart into small vesicles = separated into daughter cells

Question 29

Explain anaphase A/B

Answer 29

- A = tubulin depolymerized = chromosomes move towards poles + motor proteins at kinetochore involved - B = separation of 2 poles = non-kinetochore microtubules overlap + push against eachother = elogating cell + motor proteins involed

Question 30

Define binary fission

Answer 30

- Bacterial reproductive cell cycle - Faster than eukaryotic cell cycle - Duration = 1-3 hrs

Question 31

Describe binary fission

Answer 31

- Bacterial chromosomes replicate - 2 daughter chromosomes actively move apart = at each end - Plasma membrane grows inwards = new cell wall