most cells in the body have a nucleus. The nucleus contains the
genetic material in the form of chromosomes
chromosomes are coiled up lengths of DNA molecules.
each chromosomes carries a large
number of genes. Different genes
control the development of
different characteristics.
body cells normally have 2 copies of each chromosomes
one from the organism's 'mother'
one from the organisms 'father'
so humans have 2 copies of chromosome 1 and 2 copies of chromosome 2
humans have 23 pairs of chromosomes
the cell cycle makes new cells for growth,
development and repair
body cells in multicellular organisms divide to produce new cells as
part of a series of stages called the cell cycle
the stage of the cell cycle when the cell divides is called
mitosis
multicellular organisms use
mitosis to grow or replace cells
that have been damaged
the end of the cell cycle results in 2 new identical daughter
cells, with the same number of chromosomes
growth and DNA replication
in a cell that's not dividing, the DNA is all
spread out in long strings.
Before it divides, the cell has to grow and increase
the amount of subcellular structures such as
mitochondria and ribosomes
it then duplicates its DNA - so there's one copy
for each new cell. The DNA is copied and
forms X - shaped chromosomes. each 'arm' of
the chromosome is an exact duplicate of the
other.
mitosis
once its contents and DNA have been copied the
cell is ready for mitosis
the chromosomes line up at the centre of the cell and
cell fibres pull them apart.
the 2 arms of each chromosome go to opposite ends of the cell
membranes form around each of the sets of
chromosomes.
these become the new nuclei of the 2 new cells - the nucleus has
divided
lastly, the cytoplasm and cell membrane divide.
the cell has now produced 2 new identical daughter cells.
The daughter cells contain exactly the same DNA - they're
identical. Their DNA is also identical to the parent cell.