Mitosis and meiosis Flashcards
What is the function of mitosis?
Function of mitosis is for somatic cell division.
To enable growth and replacement of dead cells.
Mitosis is comprised of which stages? And what happens in each stage?
Prophase: Chromosomes are visible, nuclear membrane disappears and nucleolus disappears.
Metaphase: Non homologous chromosomes line up across centre. Spindle fibres attach to centr of each chromosome.
Anaphase: Chromosomes split and each half is pulled to other half of cell.
Telophase: Chromosome cluster in middle of each new cell. Nuclear membrane begins to form. Cell begins to split.
What does interphase comprise?
Preceeded by G0 phase.
- 1st gap or growth (G1)
- Synthesis (s) (DNA replication)
- 2nd gap or growth (G2)
Which cells remain in G0 for a long period of time and which hardly at all?
— many cells are in G0 for long periods of time (liver)
— others are continually dividing (epithelium, hoof)
— others divide according to regular signals (germ cells)
— others divide on demand (wounded epithelium)
What happens in G1 phase (growth phase 1) of interphase?
(G1) phase
• normal cell activities
• increase in cell organelles
• doubling of cell size
What happens in the S (synthesis) phase of interphase?
DNA is synthesised — 2 copies of each chromosome
(sister chromatids) are available.
. centrioles replicate
What happens in G2 (growth phase 2) of interphase?
Cell grows in size each cell now has 2 pairs of centrioles.
Mitotic phase starts
What are the key points of mitotic cell division?
- DNA of parent cells repilcate before mitosis begins to produce two identicai copies.
- homoiogous chromosomes do not associate with each other on the spindle.
- chromosome arrangement on the spindie ensures chromatids are eveniy distributed between daughter ceiis
At what two levels can control of the cell cycle occur?
Intracellular (checkpoints at G1, G2 and M phase) and intercellular (Mitogens, growth factors)
What causes arrest at G1 phase?
If not mitogenic signal is received or DNA is damaged.
What causes arrest at G2/M phase?
Damaged DNA or incomplete duplication.
What causes arrest at the metaphase to anaphase point?
If chromatids are not correctly attached to kinetochores.
How do intercellular growth factors work?
They are signalling molecules that bind to cell surface receptors and activate pathways which control genes.
They have multiple effects, but they are
mitogenic (stimulate mitogenesis or cell division)
They act by stimulating cells to enter G1 from G0
They originate from neighbouring cells and
maintain correct cell numbers in an organ /system.
When would a cell undergo apoptosis?
Cells undergo apoptosis when: . are damaged beyond repair . are infected with a virus . are undergoing stressful conditions (starvation) The decision comes from: . the cell itself . the surrounding tissue . cells of the immune system
Why does a mutation in p53 cause squamous Cell Carcinoma (SCC) (skin tumour)?
P53 gate keeper of cell cycle and apoptosis.
If p53 is mutated the cells can continue indefinitely to proliferate.
