DNA structure and Replication

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Race to find structure of DNA

Watson and Crick (1953)
- Linus Pauling
- Rosalind Franklin/Maurice Wilkins

X-ray diffraction was needed to elucidate structure

Crick - showed that: DNA was a constant diameter (2 nm)

Structure of DNA

- monomer unit is the nucleotide
- base pairing:
Adenine always pairs with Thymine
Guanine always pairs with Cytosine


- conservative or semi-conservative (or "dispersive"?)
- discovered to be "semi-conservative." Parent molecules stay intact.

steps of replication

- occurs with help from an enzyme: DNA polymerase strings nucleotides together
- polymerization of nucleotides is endergonic (i.e. a more complex molecule is formed)
1) each DNA strand is a template
2) bases enter at attachment point as a triphosphate
3) two phosphates are cleaved - this provides the energy needed to attach the base
4) hydrogen bonds with template base


- Point mutation: wrong base pairing
- Point mutation: added (or deleted) base

how to edit out mistakes

- damage can occur from chemicals, UV light...
- common mistakes:
- depurination (loss of G or A) (can lose 10,000/day)
- deamination
- thymine dimers - from UV radiation
...all errors result in the synthesis of a wrong protein

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