Flashcards · 9700 · AS Topic 5

The mitotic cell cycle (AS Level) flashcards

12 cards on AS Topic 5, subtopics 5.1 to 5.2. Pick a subtopic or study them all.

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Centromere vs telomere: Centromere: the region joining sister chromatids, where spindle fibres attach. Telomeres: repeated non-coding sequences at the ends of chromosomes.
Phases of the cell cycle and what happens to DNA: G1: growth, protein and organelle synthesis (DNA = x). S: DNA replication (x → 2x). G2: further growth, preparation for division (2x). Mitosis: nuclear division. Cytokinesis: the cytoplasm divides (x in each cell).
Why are telomeres needed?: Each DNA replication cannot copy the very end of the molecule, so a short piece is lost from each end every cycle. The piece lost is non-coding telomere, so genes are not lost.
Stem cell: An unspecialised cell that divides by mitosis and gives rise to cells that can differentiate. Role: replacing short-lived cells (blood cells from bone marrow) and repairing tissue (skin).
How does a tumour form?: A mutation in a gene that controls cell division means the cell no longer stops dividing. Repeated, uncontrolled mitosis produces a mass of cells, all carrying the mutation: a tumour.
Why are the daughter cells of mitosis genetically identical?: DNA is copied exactly in S phase, then each daughter nucleus receives one chromatid of every chromosome. Needed for growth, replacement, repair and asexual reproduction.

Prophase: Chromosomes condense and become visible, each as two chromatids. The nucleolus disappears, the spindle forms and the nuclear envelope breaks down.
Metaphase: Chromosomes line up on the equator of the spindle, with spindle fibres attached at the centromeres.
Anaphase: Centromeres divide and sister chromatids are pulled to opposite poles, centromere first, as the spindle fibres shorten.
Telophase and cytokinesis: Telophase: chromosomes reach the poles and uncoil; nuclear envelopes re-form; the spindle breaks down. Cytokinesis: animal cells pinch in; plant cells form a cell plate and new cell wall.
Mitosis in plant cells vs animal cells: Plant cells have no centrioles but still form a spindle. Cytokinesis in plants is by a cell plate from vesicles, not by the membrane pinching in.
How do you find the time a cell spends in one stage of mitosis?: Time in stage = (cells in that stage ÷ total cells counted) × length of the cell cycle. Assume cells divide at random times. Example: 45 of 900 cells in a 16 h cycle → 0.05 × 16 h = 0.8 h = 48 min.