Topic 10: cell cycle Flashcards
Define cell division + it’s role
- In unicellular = reproduction = binary fission
- In multicellular = growth + development + repair damage
Describe the 2 cell division processes
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
Define fertilization
- Male + female gametes fuse = zygote = complete set of chromosomes = diploid
Define cancer
- Abnormal growth = proliferates uncontrollably = metastasize
Define cell cycle
- Functional process cell goes through = divided into 2 identical daughter cells
What are the phases of the cell cycle?
1) Interphase = G1/S/G2
2) Mitotic phase = mitosis + cytokinesis
Describe G0 phase
- Resting phase = non-dividing cells
- Differentiated cells = enter G0 > G1 due to growth factors
- Cells exit G1 > G0 = to differentiate
What causes cell cycle control?
1) Extracellular signals = presence of growth factors
2) Intracellular signals = cell size
Cell types + cell division potential
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
Define interphase
- Period between cell divisions
- Largest phase of cell cycle
- Prepares cell for division OR decides if needs to proceed with division
- G1/S/G2
Define G1 phase
- Prepare for DNA replication
- Protein synthesis + organelle production
- Duration = 5-6 hrs
Define S phase
- DNA replication
- Duration = 10-12 hrs
Define G2 phase
- Prepare for cell division
- Protein synthesis + organelle production
- Duration = 4-6 hrs
Describe eukaryotic chromosomes
- Chromatin = complex of DNA + proteins = histones
- Each chromosome = 100-1000s genes
- Cells DNA = about 2m long
2 types of cells + chromosomal content
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
Define homologous chromosome
- Carry same genes at same position
Describe the distribution of chromosomes during cell cycle
- 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
5 Phases of mitosis
1) Prophase
2) Prometaphase
3) Metaphase
4) Anaphase
5) Telophase
Describe prophase
- Chromatin = condenses into visible chromosomes
- Nucleoli disappear + nuclear membrane = begins degrading
- Mitotic spindle begins to form
Describe prometaphase
- Nuclear envelope fragments
- Microtubules from centrosome bind to chromosome
- Chromosomes = more condensed
Describe metaphase
- Centrosomes = opposite poles
- Chromosomes aligned on metaphase plate = by polymerisation/depolymerisation of kinetochore
- If chromosomes not aligned properly = cell cycle arrest signal
Describe anaphase
- Sister chromatids pulled to opposite poles = due to inactivation of centromere proteins hl=olding together chromatids
- By end of anaphase = each pole = equivalent chromosomes
Describe telophase
- Nuclear envelope reforms
- Nucleoli reappears
- 2 daughter nuclei form
- Chromosomes decondense
- Mitosis completed
Describe cytokinesis in animal cells
- Forms cleavage furrow
- Contractile ring formation = ring of actin + myosin contracts = complete separation
Describe cytokinesis in plant cells
- Vesicles with cell wall material = at metaphase plate
- Cell plate formation = vesicle fusion
- Cell plate elongates = fuses with parental cell wall = creates 2 seperations
Describe mitotic spindle formation + kinetochore function
- 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
Describe the 3 types of mitotic spindles
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
Describe nuclear envelope/organelle degradation
- 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
Explain anaphase A/B
- 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
Define binary fission
- Bacterial reproductive cell cycle
- Faster than eukaryotic cell cycle
- Duration = 1-3 hrs
Describe binary fission
- Bacterial chromosomes replicate
- 2 daughter chromosomes actively move apart = at each end
- Plasma membrane grows inwards = new cell wall
