the cell cycle and cell divison

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  • the cell cycle and cell divison
    • cells and chromosomes
      • chromsome structure
        • are made of  DNA and a protein called HISTONE
        • chromsomes only become visable when chromatin condenses before cell division
        • two exsacts copies of a chromsome are called sister chromatids
        • there joined and cenromere
      • plodidy level and chromsome number
        • differnt species have a different number of chromosomes
        • human has 46, whilst a fly has 8
        • the number of chromsomes in a complete set in the hapliod number
        • get one set from mother and one set from father and they match called a homologous pair
        • humans have 23 hamologous pairs
          • 2N
    • Mistosis and the cell cycle
      • mistosis produces 2 daugter cells which are genetically identical
      • all cells divide in a regular patternt called the cell cycle
        • there are different phases interpahse, prophase metaphase anaphase telophase
          • inerphase
            • is the longest phase of the cell cycle
            • lots of metabolic activity
            • cells grow and oranelles replicate
            • chromosomes are no longer visable in a microscope as the nuclear material, chromatin, disappears
          • prophase
            • the chromosome condenses. they coil getting shorter and thicker
            • centriols are   present in animal cells, the pairs separate and move to different ends called poles
            • spindle fibers extend from pole to pole
            • the nucleoulos disaperes
            • pairs of chromatids can clearly be seen lying free in cytoplasm
          • metaphase
            • chromosomes attach to the spindle fibers at their centromeres and aline on the equator
          • anaphase
            • is a very rapid stage
            • the centromere sperate and the spindle fibers shorten pullin the now spenrated chromatids to the poles
          • telophase
            • this is the final stage of mitosis
            • chromsomes uncoil and lengthen
            • the spindle fribers break down
            • the nuclear envelpoe re forms
            • the nucleus reapers
          • shape
            • animal cells become round befpre mitosis
            • plant cells no shape change
          • cnetrioles
            • animal cells present
            • plant cells absent
          • cytokinesis
            • animal cells cleavage frrow
            • plant cells cell plate
          • spindle
            • animal cells degenerates at telophase
            • plant cells remains throughout new cll wall formation
          • occureence
            • aniaml cells bone marrow
            • plant cells in metristems
      • chromosme number
        • mitosis produces the same numberof chromosomes in the daughter nuceli as in the parent nuclei
        • the daugter nuclei is an exstact repulica of parent
      • growth
        • by producing new cells an organisms increases its cells number and can grow and repair tissues
      • asexual reproduction
        • produces offspring that are genetically identical to the parent
        • it takes place in unicelluar organisms such saw yeast and bacteria
      • damage and disease
        • if the genes that control the cell cycle are damaged cells may fail to divide or divde too frequently or at the wrong time
        • ratiation and certain chemicals and some viruses mutate DNA
        • if genes are damaged they could repucate too fast. if this happens in solid tissue a tummor is formed
          • if this happens in somewhere like bone marrow. the blood cells spill into blood circulation and can cause cancer
    • meiosis
      • takes place in the reproductive organs of plants animals and some protocactistans
      • it results in 4 geneticall distinct gametes
      • the number of chromosomes
        • in miosis the diploid number is halved to hpoliod number
        • when two hapliod gametes fuse at fertilisation the zygote that is formed has two complete sets of chromosomes
      • the significance of miosis
        • keeps the chromosme number constant throughout generations
        • meiosis genrates genetic variation in the gametes n

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