Structure, function and growth of prokaryote and eukaryote cells (ii) Cell growth and Cell cycle

1. Structure, function and growth of prokaryote and eukaryote cells • (ii) Cell growth and Cell cycle • Interphase • Mitosis • Mitotic index • Control of the cell cycle • Abnormal Cell division: cancer cells

2. CK Cell Control • There are three checkpoints in the cell cycle. • Where do you think these are and why?

3. Control of Cell Cycle • G1 Checkpoint • End of the G1 phase • Cell size is assessed • If large enough the cell enters S-phase • The cell is usually pushed past this point by signals (growth factors) from outside the cell

4. Control of Cell Cycle – G1 cont… • If conditions are met • DNA replication enzymes called polymerases are transcribed to allow S-phase to begin • If conditions are not met • Cells don’t divide and remain in G0 (roughly equivalent to G1) • Many mature cells e.g. nerve cells, skeletal muscle cells, RBCs don’t divide

5. Control of Cell Cycle • G2 Checkpoint • DNA replication success is monitored • If replication is successful • DNA polymerase enzymes are deactivated • Metaphase enzymes are activated (see MPF) • If replication is unsuccessful • Any cell with unreplicated or damaged DNA that can’t be repaired is destroyed (apoptosis = cell suicide)

6. Control of Cell Cycle - MPF • Mitosis (maturation) Promoting Factor (MPF) • Promotes transition of G2 to M phase • Acts as a catalyst for the conversion of metaphase enzymes from an inactive to an active state (by phosphorylation)

7. Control of the Cell Cycle • M Checkpoint • Occurs during metaphase • Checks the spindle has assembled properly • All chromosomes are attached properly (by the kinetochores) • If conditions are met • Metaphase enzymes are deactivated • Anaphase enzymes are activated

8. Abnormal Cell Division: Cancer • What do you already know about cancer and its causes?

9. Abnormal Cell Division: Cancer • Introduction Cancer cells by-pass normal cell control mechanisms. As a result they divide uncontrollably to form lumps of tissue (tumours) that no longer carry out their function.

10. Mutation to Proliferation Genes • Normal proliferation genes are called Proto-oncogenes • During normal cell division proto-oncogenes code for proteins (e.g. growth factors) that promote cell division

11. Mutation to Proliferation Genes… • Mutated Proliferation genes are called oncogenes • Oncogenes act to produce cells that are not required. E.g. • Produce a protein which triggers a response in the cell as if growth factors are present • Over production of growth factors

12. Mutation to Proliferation Genes… • Oncogenes are dominant • Only 1 gene in the pair of alleles needs to mutate for it to have an effect. • Mutations in several different genes are usually required for cancer to develop.

13. Mutation to Anti-proliferation genes • (AKA Tumour Suppressor Genes) • Normal Anti-proliferation Genes • Switch off cell division when something goes wrong • If the cell is damaged beyond repair apoptosis occurs

14. Mutation to Anti-proliferation Genes.. • Mutations to Anti-proliferation Genes • Cause the cell to continue dividing when faulty • E.g. p53 is a protein produced by a anti-proliferation gene. It binds to damaged DNA stopping cell division until it is repaired. A mutation to this gene results in a faulty protein and cell division with faulty DNA

15. Mutation to Anti-proliferation Genes.. • Mutations to anti-proliferation genes are recessive • Both alleles of the gene are required to be mutated for mutation to take affect • Mutations in several different genes are usually required for cancer to develop

16. Learning Activities • Write a brochure or a story to explain what cancer is to a young child (assume they know about cells). • Genetic Origins of Cancer worksheet • Advanced Higher Questions • Read Dart pg 14-17 • Scholar