DNA synthesis

  • Central Dogma of biology:

    • Information flows in one direction

  • DNA → RNA → Protein

  • involves three processes

    • replication -- copies DNA
    • Transcription -- converts DNA to RNA
    • same “language” nucleic acid to nucleic acid
    • Translation -- interprets RNA message into string of amino acids
    • changes “language” nucleic acid to protein

  • In DNA: A, T, G, C

  • In RNA: A, U, G, C

  • DNA: Deoxyribose Nucleic Acid

  • RNA: Ribose Nucleic Acid

  • Transcription

    • produces an RNA molecule from a DNA template

    • Takes place in the nucleus

    • Gene -- not entire DNA strand -- transcribed into RNA

    • Catalyzed by RNA polymerase

    • Enzyme that bonds nucleotides together

    • Steps of Transcription

    • \

      1. large transcription complex
      • RNA polymerase and other proteins
      • Unwinds segment of DNA

    • \

      1. RNA polymerase uses one strand of DNA as a template
      • RNA nucleotides form complimentary base pairs with template
      • Same base pairing rules except Uracil on RNA not Thymine

    • \

      1. completed RNA strand separates from DNA
      • transcription complex falls apart
      • DNA zips back together

    • AUG UGG CAA UAG CCC GAU

    • AUG UAC GCC UAA UGA CAU

    • Transcription makes three types of RNA

      • mRNA -- messenger RNA takes information for protein to be made from DNA to the ribosome
      • tRNA -- transfer RNA carries amino acids to ribosomes, lines them up in the correct order according to mRNA
      • rRNA ribosomal RNA makes up the structure of the ribosome

    • Replication and Transcription both very similar processes

  • mRNA processing

    • after transcription, mRNA is edited
    • Exons = gene that codes for protein (expressed) keep
    • Introns = part of DNA that does not code for a protein (intervene) throw out

  • Translation

    • translation = converting mRNA message into polypeptide

    • “language” of nucleic acids -- A G C T (U)

    • “language” of proteins " -- amino acids

    • triplet codon

    • codon = three nucleotide sequence that codes for amino acid

    • Special codons

    • stop codons -- 3 codons that signal the end of the protein: UGA, UAG, UAA

    • start codons -- 1 codon (AUG) signals the start of translation -- also codes for amino acid methionine. ^^ALWAYS START AT AUG^^

    • Reading the code

    • mRNA codon, find the amino acid on the chart

    • tRNA has “anti codons”

    • Steps of translation

    • \

      1. mRNA arrives at ribosome and attaches to small ribosomal unit
      2. tRNA with methionine binds to AUG codon – signals \n large subunit to attach
      3. mRNA pulled through ribosome one codon at a time
      4. exposed codon attracts complimentary tRNA carrying amino acid
      5. Ribosome forms peptide bond between 2 amino acids
      6. first tRNA is freed - leaves to pick up another amino acid
      7. Process continues with next exposed codon
      8. once stop codon is reached - no tRNA comes in and protein is released