3.2.2 All cells arise from other cells – AQA A Level Biology Summary Notes
Within multicellular organisms, not all cells retain the ability to divide
Once specialised, they lose the ability to divide
New cells formed from stem cells or some that retain ability eg
- Cambium in vascular tissues of plants
- Endothelial cells in gut lining of animals
Eukaryotic cells that retain ability to divide show a cell cycle
DNA replicartion occurs during interphase
Mitosis is part of cell cycle which eukaryotic cell divides to produce 2 genetically identical daughter
cells, each with identical copies of DNA, produced by the parent cell during DNA replication
Interphase (longest phase)
- Cells grow and carry out cellular functions
- Near end of interphase cells replicate their DNA, ready for cell division
- G1 – grow and carry out cell functions
- S – DNA replication
- G2 – prepares for divisions eg synthesising proteins
Nucleus then divides by mitosis, forming two identical nucleic
Cytoplasm then divides to form two new cells (cytokinesis)
Length of cell cycle varies but most cells spend 90% of time in interphase
BUT rapidly dividing cells eg in an embryo may have shorter interphase and go quickly from one
division to the next
Cells cannot progress past ‘checkpoints’ in interphase unless proto oncogenes are on and tumour
suppressor genes are off
Within multicellular organisms, not all cells retain the ability to divide
Once specialised, they lose the ability to divide
New cells formed from stem cells or some that retain ability eg
- Cambium in vascular tissues of plants
- Endothelial cells in gut lining of animals
Eukaryotic cells that retain ability to divide show a cell cycle
DNA replicartion occurs during interphase
Mitosis is part of cell cycle which eukaryotic cell divides to produce 2 genetically identical daughter
cells, each with identical copies of DNA, produced by the parent cell during DNA replication
Interphase (longest phase)
- Cells grow and carry out cellular functions
- Near end of interphase cells replicate their DNA, ready for cell division
- G1 – grow and carry out cell functions
- S – DNA replication
- G2 – prepares for divisions eg synthesising proteins
Nucleus then divides by mitosis, forming two identical nucleic
Cytoplasm then divides to form two new cells (cytokinesis)
Length of cell cycle varies but most cells spend 90% of time in interphase
BUT rapidly dividing cells eg in an embryo may have shorter interphase and go quickly from one
division to the next
Cells cannot progress past ‘checkpoints’ in interphase unless proto oncogenes are on and tumour
suppressor genes are off
