BIOLOGY - MITOSIS

Thread like structure made up of a long molecule of DNA and histone proteins, chromosomes pair up (homologus pairs) and the 23rd pair are sex chromosomes. All others are autosomes.

When a cell is not dividing, chromosomes are not visible. When they are about to divide, chromosomes condense and become invisible. They appear as two threads and joined by a centromere

Interphase, mitosis and cytokenisis

DNA of each chromosome is replicated (copies (called sister chromatids) held together at the centromere) Organelles and centrioles replicated and proteins are made and cell carries out its functions

Prophase, metaphase, anaphase and telophase

Chromosomes condense and become visible, centrioles move to opposite sides of cell in animal cells, spindle forms from microtubules and nuclear envelope disintergrates

Centromeres of chromosomes attach to spindle and line up at the equator

Spindle fibres shorten, centromere seperates and individual chromatids are pulled to the poles centromere first

Spindle breaks down, chromosomes uncoil and nuclear envelope forms

Cytokinesis is the division of the cytoplasm to create the two new genetically identical cells

Splitting happens in the centre of the cell (cytoplasm splits) due to contraction of ring made of two proteins to make a cleavage furrow

Only takes place in root and shoot tips, these cells are called meristem cells. There are no centrioles in plant cells and during cytokinesis, a cell plate (droplets of cell wall material) develop from the centre out

Prevent rapid cell division in cell tissue

Genes mutate or if the cell is infected by a virus