DNA

DNA

WHAT DOES DNA LOOK LIKE?
1. There is DNA in the nucleus of EVERY cell
2. Each long molecule of DNA is called a CHROMOSOME
3. Most people have 46 chromosomes in each of their cells.
  1. You inherit half your chromosomes form your mother and half from your father.
  2. Other Organisms are different ~ chickens have 78 chromosomes
4. Almost everyones DNA is unique.
  1. The only organisms that share identical DNA are identical twins and clones.
GENES
1. The short sections of DNA
2. They code for a charecteristic such as eye colour, whether you have freckles or dimples, or your blood group.
  1. The combination of Genes in an organism controls how the organism functions, and what it looks like.
3. The code that a gene has causes specific proteins to be made.
  1. These particular proteins determine the cell's function.
    1. E.g. the proteein haemoglobin is found in red blood cells which allows the cells to bind to oxygen to transport it around the body
WHAT IS THE STRUCTURE OF DNA?
1. DNA is made up of two strands
  1. These strands are joined together by BASES.
    1. The strands are then twisted together
      1. This forms a shape known as a double helix
    2. They are held together by BONDS between the BASES.
2. DNA is made of lots of small units called NUCLEOTIDES.
  1. These NUCLEOTIDES are joined together ~ meaning that DNA is a polymer.
    1. Each nucleotide is made up of a sugar called DEOXYRIBOSE.
      1. DEOXYRIBOSE is a phosphate group and a base.
    2. There are FOUR different types of NUCLEOTIDE in DNA ~ each containing a different base
      1. A = ADENINE
        ADENINE ALWAYS BONDS WITH THYMINE (A-T)
      2. T = THYMINE
      3. C = CYTOSINE
      4. G = GUANINE
        CYTOSINE ALWAYS BONDS WITH GUANINE (C-G)
      5. To hold the strands of DNA together a base from one strand bonds with a base on the other strand.
        This forms a base pair.
        The base pairs always bond together in the same formation.
HOW IS A COPY OF DNA MADE?
1. DNA cannot leave the nucleus of your cells as it is too big.
  1. Instead a copy of the DNA is made called mRNA
    1. mRNA is made in a process called TRANSCRIPTION
      1. The DNA around a gene unzips so that both strands are seperated
        One of the DNA strands acts as a template.
        Complementary bases attach to the strand being copied.
        E.G. CYSTOSINE (C) joins to GUANINE (G)
        This forms a strand of mRNA.
        There is no THYMINE (T) in mRNA
        So instead, a base called URACIL (U) binds with ADENINE (A)
        When complete, the strand of mRNA detatches itself from the DNA template.
        The DNA zips back up.
    2. mRNA is small enough to move out of the nucleus
      1. It travels to subcellular structures called ribosomes in the cytoplasm.
        This is where the protein will be made
HOW IS A PROTEIN MADE?
1. Proteins are made from AMINO ACIDS
  1. Different amino acids join together to form different proteins.
    1. The order of NUCLEOTIDES in your DNA determines the type and order of amino acids.
      1. This determines which proteins are produced.
2. By a process called TRANSLATION
  1. The mRNA attaches to a RIBOSOME
    1. Here the NUCLEOTIDE sequence is interpreted
      1. The new protein is made.
        The RIBOSOME 'reads' the NUCLEOTIDES on the mRNA in groups of THREE.
        These groups are called BASE TRIPLETS or CODONS.
        Each triplets codes for a SPECIFIC amino acid
        E.G. CGU codes for a different amino acid to ACG
        The RIBOSOME continues to 'read' the triplet code, adding more amino acids.
        The AMINO ACIDS join together in a chain.
        This is a PROTEIN.

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