Today’s Outline• DNA and DNA Replication Review

– Leading Strand vs. Lagging Strand– DNA Pol I vs. DNA Pol III

• Telomeres• Molecular Sculpting

– DNA Replication– PCR

• What’s Due?– StudyNotes 7 is due on Thursday Mar 21– HW # 5 and is due on Tuesday Mar 26.– StudyNotes 8a is due on Tuesday Mar 26.

hydrogen bonds

Strand

3’ carbon 3’ carbon

5’ carbon 5’ carbon

A DNA Double Helix has a regular, repeated structure

DNA Polymerase III

Adds dNTPs to the newly synthesized strand on the leading strand. Adds to the 3’ end of a ribose.

DNA Polymerase I

DNA Primase creates primers (red) that are RNA molecules. DNA Pol I replaces the RNA nucleotides with DNA nucleotides.

Ends of parental DNA strands

Leading strandLagging strand

Lagging strand

Last fragment Previous fragment

Parental strand

RNA primer

Removal of primers and replacement with DNA where a 3 end is available

Second round of replication

New leading strand

New lagging strand

Further rounds of replication

Shorter and shorter daughter molecules

5

3

3

3

3

3

5

5

5

5

53

DNA Pol1 Can only add nucleotides to the 3’ end of existing DNA.

Telomeres protect an organism’s genes from being eroded during successive rounds of DNA replication. In humans the sequence TTAGGG is repeated between 100 and 1000 times.

Molecular SculptingTwo Models:

1. DNA Replication – must include:– Helicase, topoisomerase, single strand binding

proteins, DNA primase, the sliding clamp, DNA pol I, DNA pol III and ligase.

– Okazaki fragments, RNA primers, leading strand, lagging strand, nucleotides and free dNTPs.

2. Polymerase Chain Reaction – must include:– Three panels: denaturing, annealing and extending.– DNA, forward and reverse DNA primers, taq

polymerase, dNTPs.