1. Cell Division

2. Mitosis or Meiosis Used for growth and repair of cells 2 new cells form Each daughter cell is genetically identical to the parent cell Involves 2 divisions Involves 1 division Daughter cells contain half the number of chromosomes than parent cell Sections of DNA get swapped

3. The job of cell division: For multi-cellular organisms to grow To replace worn out/damaged cells Reproduction in every organism There are 2 types: Mitosis and Meiosis

4. Mitosis is involved in: DEVELOPMENT – the formation of a multicellular organism from a single fertilised egg GROWTH – involves an increase in size through the division of cells by mitosis CELL REPLACEMENT – many cells within a multicellular organism are constantly dying and being replaced by mitosis ASEXUAL REPRODUCTION – asexual reproduction in certain plants and lower eukaryotic animals, involves the process of mitosis Budding in this species of Hydra is a form of asexual reproduction; new individuals are produced as outgrowths of the parent by the process of mitosis

5. Mitosis At GCSE: 1) Parent cell 2) Chromosomes make identical copies of themselves 3) They line up along the centre they move apart 4) Two daughter cells form with identical chromosomes to the parent cell

6. Meiosis

7. Chromosomes & their instructions Daughter cells need a full set of all these instructions in order to make new cells

8. What are the main differences between the genetic material of eukaryotes and prokaryotes?

9. DNA and histones So…Chromosomal DNA is folded and tightly bound to proteins called histones. DNA+histones=chromatin Each human chromosomes contains 1 very long DNA molecule which if unravelled would measure 4.8cm (& this is just ONE chromosomes) therefore there is a packaging problem!

10. Apart from sex chromosomes, both chromosomes in a pair contain the same genes. They are HOMOLOGOUS pairs of chromosomes. Although they contain the same genes e.g. hair colour, they may be different versions of the same gene (alleles) e.g. blue/brown hair. E.g. one chromosome may have one allele for blue eyes and the other chromosome may have the allele for brown eyes. Humans= 23 pairs of chromosomes

11. MITOSIS The nucleus divides to form 2 identical daughter cells Daughter cells are genetically identical to parent cell Used for: growth, asexual reproduction (e.g. yeast), wound healing

12. DIPLOID parent cell with one pair of homologous chromosomes 2n Chromosome from father Chromosome from mother Each chromosome duplicates (DNA synthesis) to form 2 pairs of chromatids held together by a centromere Diploid daughter cells genetically identical to parent cell

13. Mitosis is a continuous process but for convenience of description is divided into FOUR MAIN STAGES: Prophase Metaphase Anaphase Telophase Please Make Another Two The following slides describe the process of mitosis in a hypothetical animal cell that possesses two pairs of homologous chromosomes

14. Mitosis in brief: 4 phases: PMAT (In total IPMAT) Prophase-replicated chromosomes supercoil (thicken & shorten) Metaphase-Replicated chromosomes line up down the middle of the cell Anaphase-The replicas of the chromosomes are pulled apart from each other towards opposite poles of the cell Telophase-two new nuclei are formed

15. MITOSIS You need to know the different stages of mitosis in more detail. Using the textbook p140-141 for further info Make models of the different stages of mitosis with play doh Annotate each stage with information explaining what is happening

16. The cell cycle The cell cycle is an ordered set of events, culminating in cell growth and division into two daughter cells It is the sequence of events that occurs between one cell division and the next. G1 stage stands for "GAP 1“ S stage stands for "Synthesis“ G2 stage stands for "GAP 2“ M stage stands for "mitosis"

17. 3 main stages: 1)Interphase 2) Mitosis 3) Cell division (cytokinesis) Read p74-75 Kent Advanced Biology ‘The cell cycle’ and make brief notes of what happens in each of these 3 stages

18. Interphase: Cell grows, carries out functions, replicates DNA The chromosome now consists of 2 sister chromatids joined at the centromere. Around 90% of the cell cycle Mitosis: Nuclear division takes place Chromatids separate into the 2 new nuclei Cytokinesis: (Cell division) The cytoplasm divides to form 2 new daughter cells

19. Interphase: (Before mitosis) DNA replication 3 stages of interphase (G1, S & G2) What is the cell doing in G1, S and G2? Read p28 and fill in chart StageWhat happens G1 S G2

20. StageWhat happens G1Active stage, growing, proteins made, organelles replicate SDNA replicates and 2 sister chromatids form from each chromosome G2Growth till mitosis: Mitochondria divide, chloroplasts divide in plants

21. Cytokinesis: Division of the cell May occur during or after telophase The whole cell splits to form 2 new cells each one containing a full set of chromosomes identical to the parent cell. Each daughter cell is now capable of doing everything the parent cell can.

23. This cell is in Interphase The chromosomes are not visible as threads but appear as chromatin (granular material) in the nucleoplasm During this stage the cell prepares for mitosis – DNA replicates and new organelles are manufactured

24. The chromosomes have spiralised and condensed – they are shorter and thicker and visible as clear threads The nucleolus has shrunk in size Spindle fibres are beginning to form close to the nucleus and the nuclear membrane disintegrates This cell is in Prophase By late prophase the chromosomes can be seen to have replicated, with each chromosome now consisting of two chromatids

25. Each replicated chromosome lines up independently along the equator of the cell Replicated chromosomes attach to the spindle fibres by their centromeres This cell is in Metaphase Spindle fibres have grown across the cell

26. The centromeres of each chromosome replicate and the chromatids repel one another The spindle fibres contract and pull the separated chromatids to opposite poles of the cell This cell is in Anaphase

27. A single chromatid from each chromosome has reached the poles of the spindle – the chromatids are now described as chromosomes The chromosomes begin to uncoil and appear as chromatin once again; a nuclear membrane forms around each set of chromosomes Cytokinesis (division of the cytoplasm) follows telophase In animal cells this involves constriction of the cell membrane along its central axis, and division of the cell into daughter cells This cell is in Telophase In the plant cell shown in the photograph, this involves the formation of a cell membrane in the middle of the cell followed by secretion of cell wall material on either side of this membrane

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