DNA: Form and Function
DNA: Structure and replication
Understanding DNA replication – and the resulting transmission of genetic information from cell to cell, and generation to generation – lays the groundwork for understanding the principles of heredity
Understanding DNA structure and replication is a prerequisite for understanding some of the principal tools of molecular biology
I. DNA structure: Three features of DNA makes it an ideal genetic material
A. Faithful replication
B. Information content
C. Capable of change
II. The building blocks of DNA
A. Nucleotides _____________________
B. Polynucleotides _____________________
C. Complementary base pairing _____________________
III. DNA replication is semiconservative : _______________________
IV. Requirements for DNA synthesis
- dATP, dGTP, dTTP, and dCTP
- template DNA (a pre-existing single strand)
- DNA polymerase
- There are multiple forms of DNA polymerase
- The different polymerases have different activities – those with direct roles in replication are called replicases. Others have secondary roles in replication and/or repair synthesis.
- In DNA replication polymerases catalyze the polymerization of deoxyribonucleotides into a DNA chain via the formation of a phosphodiester bond between the 3'-OH of the deoxyribose on the last nucleotide and the 5' phosphate of the dNTP precursor.
- Polymerase is bound to the DNA and moves along template the strand as polynucleotide chain grows. Thus, the dNTP precursor is identified that can base pair with the nucleotide on the template DNA. The frequency of error is low, but errors can occur.
- Polymerases can have exonuclease activity (they can remove nucleotides from the 3' end of the chain). This is a proofreading mechanism. The presence of an unpaired nucleotide from the 3'OH end of the growing chain triggers exonuclease activity: the unpaired nucleotide is cleaved from the end of the growing chain by the polymerase.