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

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

Control of Cell Cycle G 1 Checkpoint G 1 Checkpoint End of the G 1 phase End of the G 1 phase Cell size is assessed Cell size is assessed If large enough the cell enters S-phase If large enough the cell enters S-phase The cell is usually pushed past this point by signals (growth factors) from outside the cell The cell is usually pushed past this point by signals (growth factors) from outside the cell

Control of Cell Cycle – G 1 cont… If conditions are met If conditions are met DNA replication enzymes called polymerases are transcribed to allow S-phase to begin DNA replication enzymes called polymerases are transcribed to allow S-phase to begin If conditions are not met If conditions are not met Cells don’t divide and remain in G 0 (roughly equivalent to G 1 ) Cells don’t divide and remain in G 0 (roughly equivalent to G 1 ) Many mature cells e.g. nerve cells, skeletal muscle cells, RBCs don’t divide Many mature cells e.g. nerve cells, skeletal muscle cells, RBCs don’t divide

Control of Cell Cycle G 2 Checkpoint G 2 Checkpoint DNA replication success is monitored DNA replication success is monitored If replication is successful If replication is successful DNA polymerase enzymes are deactivated DNA polymerase enzymes are deactivated Metaphase enzymes are activated (see MPF) Metaphase enzymes are activated (see MPF) If replication is unsuccessful If replication is unsuccessful Any cell with unreplicated or damaged DNA that can’t be repaired is destroyed (apoptosis = cell suicide) Any cell with unreplicated or damaged DNA that can’t be repaired is destroyed (apoptosis = cell suicide)

Control of Cell Cycle - MPF Mitosis (maturation) Promoting Factor (MPF) Mitosis (maturation) Promoting Factor (MPF) Promotes transition of G 2 to M phase Promotes transition of G 2 to M phase Acts as a catalyst for the conversion of metaphase enzymes from an inactive to an active state (by phosphorylation) Acts as a catalyst for the conversion of metaphase enzymes from an inactive to an active state (by phosphorylation)

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

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

Abnormal Cell Division: Cancer Introduction 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.

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

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

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

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

Mutation to Anti-proliferation Genes.. Mutations to Anti-proliferation Genes Mutations to Anti-proliferation Genes Cause the cell to continue dividing when faulty 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 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

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

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