Zusammenfassung der Ressource
B1 cells - chromosomes and mitosis
- chromosomes contain genetic information
- 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.