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All Living things pass on their genetic heritage by common processes. Lecture
Outline No. 13
DNA is the genetic material
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 from genes to proteins
Transcription
Replication
DNA

DNA

Translation
RNA

Proteins
DNA Replication
1. Polarity of sugar-phosphate backbone:
5’

2. Antiparallel sugar phosphate backbones.:
5’

3’


5’
Hydrogen bonds
3’
3’
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 Deoxynucleotides to the 3’ end.
A replicated molecule is made up of one old strand and one new one.)
4. Activated deoxynucleotides.
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 bp’s, therefore, 12 billion ATP’s / cell division!