Human biochemistry

  • Created by: i3lena
  • Created on: 12-04-15 18:36


  • A small sample of the amino acid mixture is spotted near the botom of some chromatographic paper (labeled in pencil)
  • The paper is suspended in a chromatographic tank containing a small volume of solvent, ensuring that the spot is above the level of the solvent
  • As the solvent rises up the paper by capillary action it wil pass over the spot, which wil cause amino acids to distribute themselves between the stationary phase (water in the paper) and the mobile phase (the solvent) to different extents, and so move up the paper at different speeds.
  • When the solvent reaches almost the top of the paper, its final position is marked and is known as the solvent front. 
  • The paper is removed from the tank and is sprayed with locating reagent ninhydrin
  • Most amino acids take a purple coler and cam be distinguished as seperate isolated spots up the length of the paper
  • Rf = distance moved by amino acid / distance moved by solvent

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Gel electrophoresis

  • The medium is a gel, typically made of polyacrylamide
  • The amino acid mixture is placed in wells in the centre of the gel and an electric field is applied
  • Depending on the pH of the buffer used, different amino acids will move at different rates towards the oppositely charged electrodes
  • At their isoelectric point, amino acids will stop moving as they will carry no net charge
  • When seperation is complete they can be detected by a stain or made to flurosce under UV light and identified from their position using data tables
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How does oral contraception work?

The pill contains a mixture of progesterone and estrogen and so acts to suppress the secretion of FSH and LH, which normally work in tandem to trigger ovulation. In effect, it stimulates the hormonal conditions of pregnancy.

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DNA profiling

  • DNA is extracted from source (blood, hair, etc)
  • DNA is cut into small pieces using restriction enzymes in order to detect the unique nature of the sample
  • These small pieces are called short tandem repeats (STRs) and contain short sequences of bases that are repeated variable number of times 
  • Polymerase chain reaction (PCR) is used to amplify these regionas in the DNA by making multiple copies. PCR uses
    • sequence-specific primers to bund to the DNA that has been seperated into single strands
    • a heat-stable version of hte enzyme DNA polymerase to polimerise these sections
  • The resulting DNA fragments are seperated and detected using gel electrophoresis. Due to its phosphate group, DNA carries a negative charge, allowing fragments to move towards the positive terminal by a distance that corresponds to their molecular size: shorter fragments move furthar than longer fragments
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