AQA AS Biology Unit 2 - Cell Division and the Cell Cycle

Cell division
Cell Cycle
Haploid and Diploid
Chromosomes

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Cell Division
Mitosis
o Part of a larger cell cycle
o Occurs in the nucleus of eukaryotic cells
o Responsible for growth and repair
Replaces the entire lining of the small intestine
Liver cells only divide for repairing
Nerve cell
o New cells arise by division of existing cells
o Resulting cell is capable to divide again
Meiosis
o Cell divides twice to becomes a gamete
o Will not divide any further until fertilization
Chromosomes
Humans have 46 chromosomes
Made up of 2 identical chromatids which are connected by a centromere
Contain DNA
Long and thin for replication and decoding
Become short and fat prior mitosis easier to separate due to compact form
Cell Cycle
Interphase
o Phase with highest metabolism (mitochondria have a high activity)
o Muscles never complete the whole cycle
o G1: Protein synthesis and growth (10 hours)
Preparation for DNA replication (e.g. growths of mitochondria)
Differentiation, only selected genes are used to perform different
functions in each cell
o S: DNA Replication (9 hours)
o G2: short gap before mitosis to allow organelles and proteins for mitosis to
be made (4 hours)
G0: Resting phase (nerve cells)
M-phase (mitosis)
o Mitotic division of the nucleus (prophase, metaphase, anaphase, telophase)
o Cytokinesis (division of the cytoplasm)
Mitosis
Process of producing 2 diploid daughter cells with the same DNA by copying their
chromosomes (clones)

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Chromosomes can be grouped into homologous pairs
Mitosis occurs in
o Growth
o Repair
o Replacement of cells with limiting life span (red blood, skin cells)
o Asexual replacement
Controlled process, cancers result from uncontrolled mitosis of abnormal cells
Division of the nucleus (karyokinesis) and the cytoplasm (cytokinesis) are two
processes of mitosis
Division of cytoplasm after nucleus.…read more

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Pinching of the cell membrane to create two separate cells.…read more

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