How DNA Makes Protein / Protein Synthesis - PowerPoint PPT Presentation

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How DNA Makes Protein / Protein Synthesis

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How DNA Makes Protein / Protein Synthesis Starting Facts A section of DNA that codes for a polypeptide (a gene) has it s bases in the correct order. – PowerPoint PPT presentation

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Title: How DNA Makes Protein / Protein Synthesis


1
How DNA Makes Protein / Protein Synthesis
  • Starting Facts
  • A section of DNA that codes for a polypeptide (a
    gene) has its bases in the correct order.
  • Aas are in the body because we have eaten
    protein and after digestion, the aas were
    absorbed from the small intestine into our blood.
    Cells that needed them took them in.
  • 3 stages
  • Transcription, aa activation, translation

2
  • Transcription
  • The order of bases in a gene is changed into a
    mRNA molecule
  • Where ? In nucleus
  • How ?
  • DNA unwinds and unzips (H bonds between
    complementary bases break).
  • In the nucleus there are free mRNA bases floating
    around. With the help of RNA polymerase they
    come in and temporarily complementary base pair
    with the exposed DNA bases. (N.B an exposed A
    on the DNA will have U (uracil) pair with it).
  • When the gene has been transcribed, the
    temporary H bonds break. mRNA moves away and out
    through the nuclear pores and into the cytoplasm.
  • The DNA zips up and winds up (to protect itself)

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  • Aa activation
  • This is when tRNA becomes loaded /activated
    with its correct aa.
  • Where ? - in the cytoplasm
  • How ?
  • Its correct aa matches the 3 bases at the
    bottom of the tRNA, its anticodon.
  • This is all catalysed by a specific enzyme and
    ATP energy is used.


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  • 3) Translation
  • This converts the mRNA into a line of aas that
    are in the correct order.
  • Where ? In the cytoplasm
  • How ?
  • a) The first 3 bases, codon, of mRNA is held by
    a ribosome.
  • b) The correct tRNA, carrying the correct aa
    comes along and temporarily forms H bonds during
    complementary base pairing.
  • c) The ribosome is also holding the second
    codon, its complementary tRNA comes along and
    the anticodon forms H bonds with its codon,
    during cbp.
  • d) The first aa detaches from its tRNA and goes
    and bonds to the 2nd aa.
  • The ribosome moves along and this process
    continues until the whole mRNA has been
    translated.
  • After each tRNA has left its aa there to join
    the aa line, it goes away and will get activated
    /loaded up again with another aa that is correct.

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