Transcript Cell cycle
MITOSIS The nature of replicating cells Reproduction: Not as simple as it loo Reproduction presents a major problem for cells and organisms: (how can information be transmitted faithfully to progeny) = one bit of genetic information I II III IV The information transfer problem becomes more challenging as more bits of information are incorporated into the organism = one bit of genetic information One of life’s solutions to this challenge: “Package” the bits of information into single units called chromosomes = one bit of genetic information Packaging of genetic material in prokaryotes and eukaryotes prokaryote cell eukaryote cell chromosomes © 2003 John Wiley and Sons Publishers Fig 2.4 The structure of a highly condensed, replicated chromosome. A Chromosome BASIC GENETICS • Each cell in the human body contains two sets of 23 chromosomes • Mitosis identically replicates this information • Each cell therefore has the same genetic material • Reproductive cells only have one set of chromosomes. These combine to make a new person with different genetic material to both parents The cell cycle. © 2003 John Wiley and Sons Publishers The Stages of the Cell Cycle Mitosis M stage Mitotic Stage The nucleus and cytoplasm split to make two new cells known as DIPLOID cells STAGES OF MITOSIS Every dividing tissue cell in the body is always at a stage of the cell cycle. Whether it is at :Interphase Prophase Metaphase Anaphase Telophase Diagram showing the Stages of Mitosis Cytokinesis Thus enabling the body to continuously make new body tissue for growth and repair. Prophase The Stages of Mitosis Interphase Metaphase Anaphase Telophase The Spindle A spindle is a web type structure made up of microtubule fibres. It is essential for mitosis because it arranges the chromosomes into their correct positions in preparation for cell division. Mitotic centre A cell at metaphase Microtubule a spindle Chromosomes attached to spindle during nuclear division INTERPHASE After a cell has divided, the two new cells begin the process again, the cells at this stage are in Interphase. It is divided into three mini stages:Cell cycle G1 S G2 Eukaryotic chromsome replicating PROPHASE • The chromatin (unravelled DNA) in the nucleus, condenses to form pairs of chromosomes. • As this is happening the nucleolus begins to break down • The centrioles move to opposite ends of the nucleus. • Nuclear membrane begins to break down Prophase • Chromatin condenses (remember that chromatin/DNA replicate during Interphase), the nuclear envelope dissolves, centrioles (if present) divide and migrate, the spindle forms. METAPHASE • The spindle becomes fully developed • The chromatid pairs place themselves onto individual fibres and are aligned along the centre of the spindle • The nuclear membrane has completely gone ANAPHASE • The chromatid pairs are split into two (This is done by movement of the spindle fibres) • The pairs then travel to opposite ends of the spindle • The halved chromatids are now called chromosomes TELOPHASE Two new nuclei are formed when the chromosomes reach the opposite poles of the cell The nuclear membrane is formed- the nucleolus reappears The chromosomes disperse in the nucleus REMEMBER! Interphase Prophase Metaphase Anaphase Telophase IPMAT Mitosis in animal cells. © 2003 John Wiley and Sons Publishers CYTOKINESIS Literally means, division of the cytoplasm Mitosis is the splitting of the nucleus. Cytokinesis is the splitting of cytoplasm It usually begins during ANAPHASE Kangaroo epithelial kidney cell going through mitotic division. The work of Mr Paul Maddox. The Mitosis World website. Mitosis and cell plate formation in a flattened endosperm cell of the African bloodlily Haementhus Katherininae. Observed with place contrast microscopy. The work of Shinya Inoue and Rudolf Oldenbourge.The Mitosis World Website. Cell Turnover - The speed of mitosis Although you may have seen a speeded up video of mitosis in action. One full cycle can vary between a couple of minutes to days. For example skin and epithelial cells have a rapid turnover in the human body in order to replace the ones constantly being worn away. Cells which make up organs such as the eye and the brain, need not multiply as often once they reach adult size. Click here for movies Organs which need to produce new cells continuously have the highest turnover. For example:Bone marrowproducing replacement blood cells The testes - producing semen Tumours Abnormalities can sometimes occur in cells which reproduce at a rapid rate, this in turn may lead to the formation of tumours. Tumours of any type should be considered serious. Although benign tumours do not usually cause a threat to a persons life, they can cause great inconvenience if not treated.