biology unit 2

has most things that are covered in biology as level topic 3 

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  • Created by: rima
  • Created on: 01-06-13 22:44
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  • unit 2 biology
    • prokaryotic cells
      • infolding of cell surface membrane
        • the site of respiration, as it has a large surface area for production of energy
      • plasmid
        • circle of DNA
      • capsule
        • slimy layer on the surface for protection and prevention of dehydration
      • pili
        • thin protein tubes which allows bacteria to adhere to the surfaces
      • flagellum
        • hollow cylidricle structures to move and rotate the cell
      • cell wall
        • containing  peptidoglycan
      • circular DNA
      • ribosomes
      • cytoplasm
    • eukaryotic cells
    • protein transport
    • meiosis
      • a  type of cell division where gametes with half the number of chromosomes are formed
      • genetic variation
        • independent  assortment
          • happens during meiosis 1 where chromosomes pairs as they line up
            • there are many combinations which creates genetic variation
        • crossing over
          • chromosomes come together as pairs
          • all four chromatids come into contact
          • at the contact points the chromatids break and rejoin their sections of DNA
      • chromosomes replicate before division
        • chromosomes pair up then seperate
          • chromatids seperate forming gametes
    • cell cycle
      • mitosis
        • prophase
          • chromosomes are more visible
          • nuclear envelope breaks down
          • chromosomes becomes shorter and thicker
          • spindle forms
          • centrioles position themselves at opposite sides of cell
        • metaphase
          • centromeres attach to spindle fibres
          • chromosomes move to the equator of cell
        • anaphase
          • spindle fibres shorten
          • spindle fibres pull cromatids towards the poles and are seperated
          • spindle breaks down
        • telophase
          • nuclear envelope reforms
          • chromosomes unravel
      • interphase
        • gap 1
        • gap 2
        • synthesis
      • cytoplasmic division
        • cell surface membrane constricts around the cell , till it is divided into two
    • stem cells
      • these are unspecialised cells which keep on dividing and can give rise to other cells
      • totipotent stem cells can give rise to all the cell types including embryonic cells
        • these can be  found in the early embryo
      • pluripotent stem cells can give rise to most types of cells but not embryonic cells
        • these can be found in the older embryos
          • when a blastocyst is formed the outer layer forms the placenta while the inner cell mass forms the tissues for the developing embryo
      • when cells become increasingly differentiated (specialised) they lose there capacity to develop into a wide range of cells
      • multipotent stem cells retain a certain capacity to still give rise to a varity of cell types
    • differential gene expression
      • this is where different genes are expressed
        • first a correct stimulus is given to unspecialised cells
        • secondly some genes are either switched off or on
        • thirdly mRNA is only made from the active switched on genes
        • fourthly the mRNA moves to the ribosomes and protein is made
        • this protein can alter the function and the strcture of the cells
      • as the embryo develops , cells differentiate and become specialised for one function
      • Igor and Thomas demonstrate that different genes are expressed in different cells
        • firstly they extracted mRNA from both differentiated and undifferentiated cells
        • secondly they used reverse transription to produce cDNA strands for the differentiated mRNA
        • thirdly they mixed the cDNA strands with the mRNA from undifferentiated cell , which produced double strand hybrid
        • these hybrids were then seperated finding that two cells were expressing some of the same genes and also different genes
    • cell organisation
      • cells
        • cells are specialised for a particular function
      • tissue
        • a group of specialised cells working together to carry out a particular function
      • organ
        • a group of tissues working together to carry out one function
      • organ systems
        • a group of organs working together to carry out a particular function
    • genes and environment
      • genes  interact with the environment to produce the organisms phenotype
      • phenotype is an organisms characteristics
      • discontinuous variation is     when characteristics are controlled by genes at a single locus
      • continuous  variation is usually affected by both genes and the environment
        • eg  human height meaning that there is a bigger range
          • a person may have the genes for being tall but not achieve their full potential height because of thier poor diet
      • polygenetic inheritance is when a number of genes are involved in the inheritance of a characteristic

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