transcription and translarion

• gene


  section of dna that codes for a specific polypeptide
• mutation


  random change in the arrangement or amount of genetic material in a cell. helpful or harmful
• codon


  triplet of bases on and mRNA molecule. 1 codon codes for 1 amino acid
• anti codon


  complementary base code to a codon- found on tRNA molecules
• transcription


  DNA is copied into mRNA in nucleus. first part of protein synthesis
• translation


  ribosomes use mRNA code to produce a polypeptide- second part of protein synthesis
• polypeptide


  chain of amino acids joined together by peptide bonds in a specific order or sequence
• the genetic code is universal


  same codons code for the same amino acids in almost all organisms. enables genetic engineering
• the genetic code is non-overlapping


  codons dont share bases with their neighbours- separate
• the genetic code is degenerate


  multiple codons can code for 1 amino acid. most amino acids have more than 1 codon. 64 unique codons and 20 amino acids- 2 are stop codons and dont code for an amino acid.
• stop codons


  dont code for an amino acid. UGA, UAA, UAG
• transcription- gyrase


  -unwinds DNA
• transcription- helicase


  -breaks hydrogen bonds between base pairs
• transcription- RNA polymerase


  -joins nucleotides together in sugar-phosphate backbone- phosphodiester bonds
• the bases on an mRNA molecule are complementary to those on DNA
• mRNA

  -messenger RNA

  -a 'copy' of the DNA base sequence

  -complementary to one strand of the DNA

  -single stranded

  -uracil instead of thymine
• rRNA

  -ribosomal RNA

  -ribosomes are made of rRNA and protein (2 sub units)
• tRNA

  -transfer RNA

  -small molecules

  -h-bonds make for a clover leaf shape

  -20 types- one for each of the amino acids

  -transfers amino acids to growing polypeptide chains in the ribosome in the specific order directed by mRNA
• transcription

  -helicase breaks hydrogen bonds

  -exposes bases of the complementary DNA strands

  -only one strand is copied- template strand

  -activated RNA nucleotides line up opposite their exposed complementary bases using rule

  -RNA polymerase forms phosphodiester bonds between the sugar and phosphate groups on the RNA molecule
• transcription

  -after sugar- phosphate backbone has been sealed, mRNA detaches itself from the template strand of DNA

  -2 DNA strands join back together by complementary base pairing and DNA molecule winds and forms a helix
• transcription to translation

  -mRNA moves out through a nuclear pore and attaches to a ribosome
• tRNA

  -transports amino acids to the ribosome for incorporation into a polypeptide chain

  -hydrogen bonds between complementary bases stabilise the clover- leaf shape
• tRNA

  -anti codon that is complementary to a codon on the mRNA

  -attachment site- 3 unpaired bases to which a specific amino acid can be attached

  -ensures right amino acid gets put in place to make the polypeptide
• ribosomes

  -ribosomes are made in the nucleolus from protein and ribosomal RNA in roughly equal proportions

  -large and a small subunit bound together with aid of magnesium ions

  -groove between subunits in which mRNA sits
• translation

  -mRNA enters groove in ribosome

  -large enough to fit 2 codons side by side

  -first codon- start codon

  -anticodon carrying methionine (start codon- AUG) hydrogen bonds to the first codon to begin translation
• translation

  -after start codon has been translated, a second tRNA molecule brings over amino acid and hydrogen bonds to the second codon

  -peptide bond forms between the 2 amino acids in a condensation reaction

  -ribosome moves one codon along the mRNA so that a new codon is exposed

  -third tRNA molecule brings over a 3rd amino acid which binds to the dipeptide until a stop codon is reached

  -polypeptide chain and mRNA released from the ribosome