DNA Transcription _ Protein Translation

							DNA Transcription & Protein
Translation


Honors Biology
MLHS Jacks
    DNA Transcription


   DNA must be copied to messenger RNA
    (mRNA)
   mRNA goes from nucleus to the
    ribosomes in cytoplasm
   mRNA complements known as codons
       Only 3 nucleotide “letters” long


   Remember RNA has uracil (U) instead
    of thymine (T)!
DNA Transcription

   RNA Nucleotides are linked by the
    transcription enzyme RNA
    polymerase
   Promoter: Site at which RNA
    Polymerase begins to transcribe
    gene.
   Terminator: Sequence that signals
    the end of the gene
TATA Box
   The TATA box has the
    core DNA sequence
    5'-TATAAA-3' or a
    variant, which is
    usually followed by
    three or more adenine
    bases.
   It is usually located 25
    base pairs upstream
    to the transcription
    site.
Transcription – Step I



A C G T A T C G C G T A

T G C A T A G C G C A T


    Template DNA Strands
Transcription – Step II



A C G T A T C G C G T A

U G C A U A G C G C A U



Template DNA is Matched Up with
Complementary mRNA Sequences
Transcription – Step III




U G C A U A G C G C A U

    mRNA leaves nucleus
    and goes to ribosomes
Transcription Reminders

   The template strand is the DNA
    strand being copied
   Three phases: Initiation, Elongation
    and Termination
Protein Translation

   Modified genetic code is “translated”
    into proteins
   Codon code is specific, but
    redundant!
       20 amino acids
       64 triplet (codon) combinations
tRNA in cytoplasm has a codon
attached to an amino acid
tRNA structure

   3-base code (triplet) is an
    “anticodon”
   Protein molecule
   Attached amino acid that is carried
    from cytoplasm to ribosomes
Protein Synthesis
   Start: Ribosome binds to mRNA at
    start codon (AUG)
   Elongation:
       tRNA complexes bind to mRNA codon
        by forming complementary base pairs
        with the tRNA anticodon
       The ribosome moves from codon to
        codon along the mRNA.
       Amino acids are added one by one
   Release: release factor binds to
    the stop codon
   UAG = Stop (period)       CCG = is      CGC = water
    AUG = Initiator (Start)   CCU = subject CGG = every
    AAA = Your                CGA = drink   CGU = day
    AAC = mother              AAG = wears   AAU = dresses
    ACG = funny               ACC = have    ACU = dog
    ACA = breath              AGA = the     AGG = are
    AGU = Beatles             AGC = best    AUA = rock
    AUC = band                AUU = an      AA = old
    CAC = rubber              CAG = breaks CAU = pulled
    CCA = when                CCC = Biology CUA = I
    CUC = love                CUG = roll    CUU = music
    GAA = all                 GAC = demented GAG = puppies
    GAU = and                 GCA = so      GCC = much
    GCG = fun                 GCU = education
   GGA = door
    GGC = to                  GGG = future   GGU = father
    GUA = a                   GUC = dress    GUG = brother
    GUU = nothing             UAA = we       UAC = in
    UAU = this                UCA = together
   UCC = must
    UCG = be                  UCU = informed
   UGA = around
    UGC = you                 UGG = read       UGU = little
    UUA = DNA                 UUC = code       UUG = for
    UUU = life