A-LEVEL NOTES
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A-LEVEL NOTES

A-LEVEL BIOLOGY AQA NOTES 
all cells arise from other cells


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Cell Division
  • Within multicellular organisms, not all cells retain the ability to divide
  • The eukaryotic cell cycle has three main stages:
  • Interphase consists of two growth phases (G1& G2) and a DNA synthesis stage (S). The cell may exit the cell cycle at G0
  • Mitosis is the nuclear division
  • Cytokinesis is when the cell splits in two, forming two identical daughter cells.

Stage
Description
Prophase
​DNA condenses & coils, nuclear envelope breaks down, centrioles move to opposite poles
Metaphase
Spindle fibres attach to centromeres & chromosomes line at the equator
Anaphase
Centromeres divides, chromatids move to opposite poles
Telophase
​Chromosomes uncoil, nuclear envelope reforms
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  • Cancerous cells have uncontrolled cell division and hence have a modified cell cycle – one that repeats too quickly.
  • Treatments for cancer involve disrupting the cell cycle (chemotherapy) by stopping DNA synthesis or by changing the cytoskeleton in mitosis

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