1. Cell growth, cell cycle and differentiation 1 Cell division – does this look familiar?

2. Cell growth, cell cycle and differentiation 2 G1, S, and G2 are collectively called interphase. M is the mitotic division phase. S for synthesis; G1 stands for gap 1, or presynthesis; G2 for gap 2, or postsynthesis;

3. Cell growth, cell cycle and differentiation 3 Cell Cycle Cells that are growing and dividing go through a repeating series of events called the cell division cycle (or cell cycle). During the first phase G1, the cell grows, producing proteins and more cell organelles and prepares for DNA replication. During the S phase chromosomes replicate themselves. During the G2 phase further growth takes place with more organelles being formed. During the M phase mitosis occurs.

4. Cell growth, cell cycle and differentiation 4 Interphase G 1, S, G 2 Cytokinesis Mitosis Prophase Metaphase Anaphase Telophase

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6. 6 Mitosis Prophase Spindle fibres appear, chromosomes condense spindle fibres attach to chromosomes MetaphaseChromosomes align on equator AnaphaseSister chromatids move to opposite poles as centromeres divide TelophaseNuclear membrane reforms, chromosomes decondense, spindle fibres disappear Cytokinesis Cytoplasm divides, 2 daughter cells formed with identical genetic information.

7. Cell growth, cell cycle and differentiation 7 Control of cell cycle During metaphase in M phase (M checkpoint) proteins for mitosis are synthesised and alignment of chromosomes must be correct to progress. End of G 2 (G 2 checkpoint) DNA synthesis must be correct to progress to M phase. Near end of G 1 (G 1 checkpoint) some cell growth and proteinsynthesis must have occurred before entering S phase. Insufficient growth may mean it goes to G o phase non dividing.

8. Cell growth, cell cycle and differentiation 8 What other controls are there for cell growth? Anti-proliferation genes (tumour supressor genes) code for proteins to restrict cell growth. These proteins would stop cells from growing and dividing too much. Proliferation genes (proto-oncogenes) code for essential proteins in division. These proteins would stimulate cell growth and cell division.

9. Cell growth, cell cycle and differentiation 9 Why do cells divide? Where do cells divide? What are meristems? What does totipotent mean? What is gene expression? Are all cells totipotent? What example of genetic control of cells are you familiar with? Questions, questions …… What is differentiation?

10. Cell growth, cell cycle and differentiation 10 Tumours form spontaneously but increased incidence caused by UV light, X-rays, other mutagenic agents e.g. chemicals Malignant can break into blood stream and spread tumours throughout the body. Benign not usually as serious and removable with surgery. Cancer cells exhibit abnormal cell division. Tumours develop when control of cell division and growth is lost. Abnormal Cell Division

11. Cell growth, cell cycle and differentiation 11 What happens when cells go wrong? Anti-proliferation genes (tumour supressor genes) can mutate. Mutations in both alleles can prevent enough of these proteins being made. Mutations are recessive so both alleles need mutations for affects to be seen. Proliferation genes (proto-oncogenes) can mutate forming oncogenes. More protein is produced than normal meaning cell growth is stimulated. Mutations are normally dominant so only one allele needs to be affected.

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13. Cell growth, cell cycle and differentiation 13 Root tip Cells to be seen

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