C6 - Cell division
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What are the phases of the cell cycle?
Interphase Mitotic phase
What is interphase
Growth period of the cell consisting of stages G1, S and G2, between cell division
What happens during interphase?
-DNA replicated and checked for errors in the nucleus -Protein synthesis occurs in the cytoplasm -Mitochondria (and chloroplasts) grow and divide -Normal metabolic processes of cells also occur
What is the G1 stage?
First growth stage - proteins which synthesise organelles are produced and organelles replicate, the cell increases in size
What is the S phase?
Synthesis phase - DNA is replicated in the nucleus
What is the G2 phase
Second growth phase - cell continues to increase in size, energy stores are increased and duplicated DNA is checked for errors
What is the mitotic phase
Period of cell division consisting of mitosis and cytokinesis
What happens during mitosis
Nucleus divides
What happens during cytokinesis
Cytoplasm divides and two new cells are produced
What is G0
Phase when cell leaves the cycle permanently or temporarily?
What are the reasons for a cell entering G0
-Differentiation: cell that becomes specialised to carry out a specific function is no longer able to divide -DNA of cell may be damaged: no longer viable -Aging: growing number of senescent cells
What are checkpoints?
Control mechanisms of the cell cycle
Where do checkpoints occur?
G1 checkpoint- end of G1 phase, before entry into S phase G2 checkpoint- end of G2 phase, before mitotic phase Spindle assembly (metaphase) checkpoint- when all chromosomes attached to spindles and aligned
What does G1 checkpoint check?
Cell size Nutrients Growth factors DNA damage
What does G2 checkpoint check
Cell size DNA replication DNA damage -If passed, signals beginning of mitosis
What does spindle assembly checkpoint check?
Chromosome attachment to spindle -Mitosis cannot proceed if checkpoint isn’t passed
What is mitosis?
Nuclear division stage in cell cycle Creating two genetically identical daughter cells
What is mitosis important for?
Asexual reproduction Growth Tissue repair
What has to happen before mitosis can occur? (chromosomes)
Interphase - DNA in nucleus replicated Each chromosome is converted into two identical DNA molecules called chromatids Chromatids joined together at region called centromere
What are the four stages of mitosis
Prophases Metaphase Anaphase Telophase
What happens to chromosomes through mitosis
What happens during prophase?
1) Chromatin fibres coil and condense to form chromosomes 2) Nucleolus disappears 3) Nuclear membrane begins to break down 4) Protein microtubules form spindle-shaped structures linking poles of cell -Animal and some plants: centrioles migrate to poles and form spindles 5) Spindle fibres attach to specific areas on centromeres and move chromosome to centre of cell 5) By end, nuclear envelope disappeared
What happens during metaphase?
1) Chromosomes moved by spindle fibres to form a plane in the centre of the cell (metaphase plate) 2) Held in position
What happens during anaphase?
1) Centromeres holding together pairs of chromatids in each chromosome divide 2) Chromatids separated and pulled to opposite poles by shortening spindle fibres
