Lecture 13
Back Home Next

 

All Living things pass on their genetic heritage by common processes.
DNA is the genetic material. Lecture Outline 13

1. "One gene-one polypeptide" theory (see "one gene-one enzyme" theory).
    George Beadle and Edward Tatum (late 40’s to early 50’s) used X-rays to induce mutations in Neurospora crassa, which were unable to synthesize amino acid and vitamins. They traced the defect to the enzymes involved in their synthesis.

2. Hershey-Chase (1952) experiment extended Avery, Macleod and McCarty’s evidence that DNA is the genetic material.
        Bacteriophage is a DNA bacterial virus of E. coli.
Protein (S35) or DNA (P32)-labeled viruses were used to infect E. coli.
        Blended to separate viruses and bacteria followed by centrifugation:  Protein remained outside the bacteria; DNA inside the bacteria.

The normal flow of information

   Transcription Translation
DNA Þ RNA Þ Proteins
Replication ß
DNA

DNA Replication
1.  Polarity of sugar-phosphate backbone: 5’ ® 3’
2.  Antiparallel sugar phosphate backbones: 5’ ® 3’

Hydrogen bonds

½ ½ ½ ½ ½ ½
3’ ® 5’


3. DNA strands unwind at replication fork.
Separated strands are templates for replication: A’s to T’s and G’s to C’s.
DNA polymerase adds nucleotides to the new strands
       

4. Activated nucleotides.
        Each entering nucleotide is an activated deoxynucleotide triphosphate..
                dATP. dTTP, dGTP and dCTP.
        Nucleotide activation requires 2 ATP’s
                (i.e. dGMP + 2 ATP ®  dGTP + 2 ADP)
        Each base pair (b.p.) addition requires 4 ATP’s.
                 Human genome: 3 billion b.p.’s, therefore, 12 billion ATP’s / cell division!