Title: The cell cycle and apoptosis 15 th January 2014

1. Title: The cell cycle and apoptosis15th January 2014 Learning question: What happens in interphase? What is apoptosis? Homework: Read pages 64-67 and answer textbook questions for Friday 17th January. Make sure you mark the questions please! Starter: Can you arrange these images in sequence? 1 5 3 2 4 3,1,4,5,2

2. Learning outcomes (a) describe the cell cycle, with reference to interphase (G1,S and G2), mitosis and cytokinesis leading to diploid cells; (b) describe the structure of DNA and explain the importance of complementary base pairing and hydrogen bonding; (c) explain how DNA replicates semi- conservatively during the S phase of the cell cycle (HSW1); (d) outline the processes taking place at the G1 and G2 points in the cycle; (e) describe the appearance of the components of the nucleus and cell during mitosis with reference to: nuclear envelope, centrioles, spindle fibres, centromere, chromatids and chromosomes; (f) define the term apoptosis; (g) state that cell deletion by apoptosis and cell addition by mitosis are essential for normal growth and repair;

3. The Cell Cycle • The majority of the cell cycle is interphase and it is divided into the following parts: • G1 • S • G2 Mitosis only accounts for a small part of the total cell cycle.

4. G1 and S • G1 - First growth phase • Proteins are made • Proteins are used to build organelles • More cytoplasm is made • S – synthesis • DNA is replicated

5. G2 & M • G2 – second growth phase • Cell organelles grow and divide • Cell builds up energy stores • M – mitosis phase • Nucleus undergoes mitosis and then cytokinesis (cell division

6. Control of Cell Cycle • To know when one phase has ended and when to start the next, there are a series of checkpoints. • In a cell, these checkpoints are proteinsand enzymes. • Proteins that signals the start of the next phase are call cyclins • Enzymes that activate cyclinsare called cyclin-dependent kinases (CDKs) Cyclins + CDKs = next phase activation

7. Important checkpoints • G1 checkpoint • Late G1 triggers initiation of S phase • Replication of organelles • G2 checkpoint • Late G2 triggers mitosis • M(etaphase) checkpoint • Controls entry to anaphase

8. Signal Control of Cell Cycle • Internal and external signals cue the assembly or disassembly of the cyclin-CDK completes

9. Signal Control of Cell Cycle • What would happen to the cell cycle if a defective mitotic CDK was produced, resulting in a deformed active site? • Mitotic cyclin would not be able to bind to the active site • The initiation of the M phase would not result • Mitosis phase may not occur / occurs at a very slow rate

10. Signal Control of Cell Cycle • Stopping the cell cycle can be helpful – why? • Allows DNA repair to take place • In some forms of breast cancer, over-stimulation of Ck4 (a CDK) leads to increased cell division • The protein p53 in a helpful protein that inhibits cell division. • In over 50% of cancers contain a defective p53 gene

12. Apoptosis • Apoptosis is programmed cell death in development • Series of biochemical events leading to an orderly and tidy cell death • Hayflick Constant • Cells undergo about 50 mitotic divisions before apoptosis • Necrosis • Untidy and damaging cell death occurring after trauma

14. Sequence of Apoptosis • Enzymes breakdown cell cytoplasm • Cytoplasm becomes dense • Organelles are tightly packed • Cell surface membrane changes and blebs form • Chromatin condenses, nuclear envelope breaks • Cell breaks into vesicles • phagocytosis

15. Apoptosis

16. Apoptosis

17. Control of Apoptosis • Apoptosis is controlled by cell signalling • Cytokines from the immune system • Hormones and growth factors • Nitric oxide • Makes inner mitochondrial membrane more permeable to hydrogen ions

18. Apoptosis and tissue development • The rate of cells dying should balance the rate of cells produced by mitosis • Not enough apoptosis leads to the formation of tumours • Too much leads to cell loss and degeneration • Cell signalling plays a role in maintaining the correct balance

19. Apoptosis in Development • The formation of the digits (fingers and toes) occurs due to apoptosis during the development of the embryo.

20. Apoptosis and metamorphosis • As tadpoles grow they develop legs, change their body shape and lose their tails • The tail is lost by apoptosis

22. APOPTOSIS L/O: What is it? Why is it important? How is it controlled? What is its role in age-related disease? Apoptotic and necrotic cells, respectively

23. APOPTOSIS Programmed cell death Orderly cellular self destruction Process: as crucial for survival of multi-cellular organisms as cell division

24. Quick Questions • What word means “programmed cell death”? • Give an example of apoptosis in the human body • What would happen if the rate of apoptosis exceeded the rate of mitosis? Use whiteboards to show your answers

25. Tasks • Create a flow diagram of the stages that a cell goes through during apoptosis. • Make a list of key words for apoptosis then write a description or definition for each. • Summarise apoptosis and its role in development. • Be sure to include any examples; • The consequences of too much/too little apoptosis; • Explain why cells commit apoptosis.