The Cell Cycle 1. How do cells know when to divide? The cell cycle is an ordered programme of events that causes a cell to first duplicate itself and then divide to produce two daughter cells. In humans this, together with cell differen:a:on, allows a single-­‐celled fer:lised egg to develop into an adult human containing 100 trillion cells. It also enables the dividing cells in your body to renew themselves -­‐ you lose 500 skin cells every second and these all need replacing! The following stages make up the cell cycle: Interphase, where cells grow and prepare to divide, they also replicate their DNA; Mitoisis, where chromosomes are divided equally between the daughter cells; and Cytokinesis where the two cells are physically separated. 2. Using microorganisms to study the cell cycle The fission yeast, S. pombe, is a distant cousin of baker’s yeast (used in bread and beer making) – pombe means “from beer” in Swahili. Sir Paul Nurse won the Nobel prize for using fission yeast to work out the underlying biochemical regula:on of the cell cycle. Incredibly, the key players in this process are the same in yeast as they are in humans. What do you think might be the advantages of using yeast as a model system? Gap 2 3. Cell cycle checkpoints Control mechanisms known as checkpoints ensure the cell cycle proceeds accurately. These surveillance systems stop the cycle if something is wrong and also ensure that direc:onality through the cycle is maintained. Perturbing the func:on of these checkpoints is known to play a role in cancerous tumour forma:on. Mito4c checkpoint monitors correct a]achment of chromosomes to the mito:c spindle Mitosis Gap 1 G2/M checkpoint monitors DNA replica:on and damage In today’s session we will look at 2 of the checkpoints in the fission yeast cell cycle -­‐ the G2/M and mito:c checkpoints. We will iden:fy both an ac:vator and an inhibitor of the G2/M transi:on by using cells containing temperature sensi:ve mutant alleles and measuring cell length. We will also iden:fy ac:vators of the mito:c checkpoint using fission yeast cells containing fluorescently-­‐tagged proteins (like those above). This session will provide an introduc:on to wide-­‐field fluorescence microscopy and how to make simple measurements in imaging soUware. John Meadows 2015