5. biochemical relationships

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BIOCHEMICAL RELATIONSHIPS

  • scientists now analyse structure of many diff chemicals (e.g. proteins) in organisms, alongside DNA, to find relationships between of organisms

  • known as molecular phylogeny- not all scientists interpret results in same way

  • evidence from molecular phylogeny might support or conflict with relationships based on morphology

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GEL ELECTROTROPHES 1

  • comparisons between the AA sequences of similar proteins in diff species are also used to classify them or trace their evolutionary pathways

  • this is a variation of chromatography which is used to separate DNA or RNA fragments, proteins or AAs according to their size and charge

  • chemicals to be compared are placed in wells in a gel medium in a buffering solution

  • known DNA or RNA fragments, proteins or AAs are also placed in as a comparison

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GEL ELECTROTROPHES 2

  • for identifying DNA, the big DNA molecule is cut using restriction endonuclease enzymes- cut the DNA at specific sites

  • DNA fragments are then added to the gel containing a dye (e.g. EtBr, ethidium bromide)- binds to fragments

<ul><li><p>for identifying DNA, the big DNA molecule is cut using <mark data-color="green" style="background-color: green; color: inherit">restriction endonuclease enzymes</mark>- cut the DNA at specific sites</p></li></ul><p></p><ul><li><p>DNA fragments are then added to the <mark data-color="green" style="background-color: green; color: inherit">gel </mark>containing a dye (e.g. EtBr, ethidium bromide)- binds to <mark data-color="green" style="background-color: green; color: inherit">fragments</mark></p></li></ul><p></p>
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GEL ELECTROTROPHES 3

  • electric current is passed through the gel and DNA fragments move towards the pos electrode (anode) because DNA is neg charged due to its phosphate group

  • fragments move at different rates depending upon their mass and charge

  • once the electrophoresis is complete the plate is placed under UV and DNA fluoresces so the patterns of bands can be identified- can be compared to known samples

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MORE BIOCHEMICAL RELATIONSHIPS

  • evidence from biochemistry is playing an important role in extending our understanding of classification and evolution

  • vertebrates and echinoderms (star fish, sea urchins etc.) appear from morphological evidence to come from one line of ancestors and the annelid worms, molluscs and arthropods (including insects) from another

  • biochemical evidence appears to confirm this unlikely relationship- shows that phosphagens, molecules that provide the phosphate group for the synthesis of ATP in muscles, are of 2 different sorts

  • phosphocreatine occurs almost exclusively in the muscles of vertebrates and echinoderms whist phosphoarginine occurs in the other groups

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MORE BIOCHEMICAL RELATIONSHIPS- BLOOD

  • analysis has shown that any one group contains only one type of blood pigment

  • all vertebrate and many of the invertebrates have haemoglobin, all polychaete worms have chlorocruorin and all molluscs and crustaceans have heamocyanin

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MORE BIOCHEMICAL RELATIONSHIPS- DNA

  • analysis of the sequence of AAs in particular proteins can help show the relationship within higher groups such as a phylum

  • single AA changes are used to plot relationships

  • combination of DNA analysis and protein analysis can bring some unlikely relationships to light