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Summary BASICS- mitosis and meiosis
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It is a detailed summary of one of the important topics- mitosis and meiosis which is a conceptual organised note which also includes simple diagrams and examples.
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MITOSIS AND MEIOSISThe Cell Division Cycle
Cell division cycle, figure from Wikipedia. Cells that stop dividing exit the G1 phase of the cell cycle into a
so-called G0 state.
Cells reproduce genetically identical copies of themselves by cycles of cell growth and
division. The cell cycle diagram on the left shows that a cell division cycle consists of
4 stages:
G1 is the period after cell division, and before the start of DNA replication.
Cells grow and monitor their environment to determine whether they
should initiate another round of cell division.
S is the period of DNA synthesis, where cells replicate their chromosomes.
G2 is the period between the end of DNA replication and the start of cell
division. Cells check to make sure DNA replication has successfully
completed, and make any necessary repairs.
M is the actual period of cell division, consisting of prophase, metaphase,
anaphase, telophase, and cytokinesis.
Chromosomes
Chromosomes were first named by cytologists viewing dividing cells through a
microscope. The modern definition of a chromosome now includes the function of
heredity and the chemical composition. A chromosome is a DNA molecule that
carries all or part of the hereditary information of an organism. In eukaryotic cells,
the DNA is packaged with proteins in the nucleus, and varies in structure and
appearance at different parts of the cell cycle.
Chromosomes condense and become visible by light microscopy as eukaryotic cells
enter mitosis or meiosis. During interphase (G1 + S + G2), chromosomes are fully or
partially decondensed, in the form of chromatin, which consists of DNA wound
around histone proteins (nucleosomes).
, In G1, each chromosome is a single chromatid. In G2, after DNA replication in S
phase, as cell enter mitotic prophase, each chromosome consists of a pair of identical
sister chromatids, where each chromatid contains a linear DNA molecule that is
identical to the joined sister. The sister chromatids are joined at their centromeres,
as shown in the image below. A pair of sister chromatids is a single replicated
chromosome, a single package of hereditary information.
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