DNA keypoints

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How the structure of DNA is related to its functio

>the sugar-phosphate backbone

>its a very long molecule-so it can store lots of information

>complementary base pairing allows it to replicate accurately

>bases are held together by weak hydrogen bonds- unzip easily

>double helix makes the molecule stable

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Experiements that DNA is a hereditary material

Hammerling: cut cells of two different acetabularia in half- part of the cell died part regenerated into a whole new cell. He concluded that the information needed to regenerate the whole cell must be in the 'foot' (contained nucleus)

Fred griffith:carried out work on different strains of bacteria some were virulent some were non-virulent. virulents strains have slimy capsules but the non virulent strains do not.

virulent S strain=died                         killed S strain=survived

non virulent R strain=survived      dead S strain + living R strain=died


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  • ribonucleic acid
  • single polynucleoide strand
  • contains uracil
  • contains sugar-ribose
  • DNA carries the blueprint for the whole organism
  • Three bases code for one amino acid- the sequence of baes in a length of DNA codes for the order of amnio acids in the protein
  • A gene is a section of DNA that codes for a protein the bases sequence of a gene is copied into a molecule of DNA-
  • because its single stranded /shorter it can pass thorugh nuclear pore easily-it carries information in the DNA to the ribosome- next RNA brings amino acids to the ribosome and joins them together in the right order -so the correct protein can be made.
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Genes and Proteins

  • each cell has a homologus pair of chromosomes
  • a gene is a section of DNA that carries coded information for a characteristic
  • genes oour at the same locus on homologus chromosomes
  • an allele is an alternative form of a gene- gene for eye colour may have 2
  • genes influence the phenotype of an organism
  • cystic fibrosis-inherited condition cause by faulty CFTR protein (recessive disorder)
  • CF allele has three nuclotides missing (1 amino acid) so it produces a protein with one amino acid missing,so the protein is a different shape so it cannot function properly.
  • some genes code for proteins that act as enzymes , enzymes have a specifically shaped active site so it can catalyse reactions- active site depends on tertiary structure- this is  determined by order of amino acids -this is determined by sequence of bases in DNA.
  • an enzyme with a slightly different base sequence can cause the substrate to no longer fit the active site by altering the sequence of amino acids and tertiary structure.
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DNA replication

  • DNA replicates by the semi-conservitive method- one old and one new strand
  • process: dna strands seperate and the hydrogen bonds break between bases, free nucleotides attracted to complementary bases, once they are lined up DNA polymerase joins them together, all nucleotides joined to form complete polynuceotide chain - two identical strands of DNA formed.
  • conservative replication- old strand stayed intact new strand made from new nucleotides
  • dispersive replication-original DNA molecule would break down -nucleotides replicated two identical molecules asembled -each daughter molecule is a mixture of old and new nucleotides.
  • investigation of DNA replication:generation 1 forms midway band between light and heavy DNA - molecules have one light and one heavy strand.... generation 2 shows a midway band and a light band
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