Summary
Summary The mitotic cell cycle
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- CIE
Biology A level revision notes on mitotic cell cycle
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The mitotic cell cycleNuclear division combined with cell division allows cells, and therefore whole
organisms to reproduce. It also allows multicellular organisms to grow.
Chromosomes
Before a eukaryotic cell divides the chromosomes gradually become visible in
the nucleus.
Structure:
Right before cell division the chromosome is a double structure made of 2
identical chromatids joined together
This is because during interphase, each DNA molecule in the nucleus
makes an identical copy of itself
Each chromatid contains one of the DNA copies
The 2 chromatids are joined by a centromere, forming a chromosome
Each chromatid contains one DNA molecule. DNA is the molecule of inheritance
and is made up of a series of genes. Each gene is one unit of inheritance, coding
for one polypeptide that is involved in a specific aspect of the functioning of the
organism.
When the cell divides, one chromatid goes to one daughter cell and the other
goes to another daughter cell. As the chromatids are identical then the daughter
cells are also identical.
The DNA is wound around the outside of protein molecules in order to fit into
the nucleus. The combination of DNA and proteins is called chromatin.
Chromosomes are made up of chromatin, this is easily stained to be seen under a
microscope.
DNA coils and folds itself into a nucleosome. Just before cell the division the
chromosomes are the most tightly coiled form of DNA. Chromatin exists in 2
forms:
Euchromatin – loosely coiled
Heterochromatin – tightly coiled, seen at cell division, genes are mostly
inactive
During interphase the majority is in the form of euchromatin and where the
active genes are located.
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