4Cell replication

‘Spray-on skin’

Figure 4.4 ‘Spray-on skin’ or CellSpray, developed by Dr Fiona Wood. Skin cells taken from a patient are cultured and allowed to replicate.A suspension of these cells is sprayed onto burnt areas where they continue to grow and form a new skin.

ODD FACTIt has been estimated that each person replaces, on average, 18 kg of skin cells during alifetime. Dandruff, skin cellsfrom our scalps, represents justa fraction of the skin cells wemust replace.

Nuclear division leads toreproduction of cells

• Cells reproduce during the cell cycle.• Cells can reproduce only if the genetic

material is replicated.• The duplication of cells involves mitosis and

cytokinesis.• The two newly formed cells each have the

same kind and amount of genetic material as the parent cell.

• Each species has a characteristic chromosome number.

How long is a cell cycle?Figure 4.9 The total time taken forone mitotic cell cycle can vary greatlyfrom organism to organism. Note thecheckpoints at which there appearsto be self-checking to ensure thatmistakes have not occurred duringthe synthesis of DNA or replicationof the cell.

• Mitosis occurs in a range of different tissues in different plants and animals.

• Some eukaryotes reproduce asexually from a single cell.

• Uncontrolled cell replication can lead to cancers.

New liverworts from cells in a cup