DNA

DNA

1. WHAT DOES DNA LOOK LIKE?

   • There is DNA in the nucleus of EVERY cell
   • Each long molecule of DNA is called a CHROMOSOME
   • Most people have 46 chromosomes in each of their cells.
     • You inherit half your chromosomes form your mother and half from your father.
     • Other Organisms are different ~ chickens have 78 chromosomes
   • Almost everyones DNA is unique.
     • The only organisms that share identical DNA are identical twins and clones.

2. GENES

   • The short sections of DNA
   • They code for a charecteristic such as eye colour, whether you have freckles or dimples, or your blood group.
     • The combination of Genes in an organism controls how the organism functions, and what it looks like.
   • The code that a gene has causes specific proteins to be made.
     • These particular proteins determine the cell's function.
       • 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

3. WHAT IS THE STRUCTURE OF DNA?

   • DNA is made up of two strands
     • These strands are joined together by BASES.
       • The strands are then twisted together
         • This forms a shape known as a double helix
       • They are held together by BONDS between the BASES.
   • DNA is made of lots of small units called NUCLEOTIDES.
     • These NUCLEOTIDES are joined together ~ meaning that DNA is a polymer.
       • Each nucleotide is made up of a sugar called DEOXYRIBOSE.
         • DEOXYRIBOSE is a phosphate group and a base.
       • There are FOUR different types of NUCLEOTIDE in DNA ~ each containing a different base
         • A = ADENINE
           • ADENINE ALWAYS BONDS WITH THYMINE (A-T)
         • T = THYMINE
         • C = CYTOSINE
         • G = GUANINE
           • CYTOSINE ALWAYS BONDS WITH GUANINE (C-G)
         • 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.

4. HOW IS A COPY OF DNA MADE?

   • DNA cannot leave the nucleus of your cells as it is too big.
     • Instead a copy of the DNA is made called mRNA
       • mRNA is made in a process called TRANSCRIPTION
         • 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.
       • mRNA is small enough to move out of the nucleus
         • It travels to subcellular structures called ribosomes in the cytoplasm.
           • This is where the protein will be made

5. HOW IS A PROTEIN MADE?

   • Proteins are made from AMINO ACIDS
     • Different amino acids join together to form different proteins.
       • The order of NUCLEOTIDES in your DNA determines the type and order of amino acids.
         • This determines which proteins are produced.
   • By a process called TRANSLATION
     • The mRNA attaches to a RIBOSOME
       • Here the NUCLEOTIDE sequence is interpreted
         • 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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