DNA: The Genetic Material

Chapter 14

DNA

•DNA made up of nucleic acids.

–Five carbon sugar, phosphate group, organic base.

•Purines - Large bases

–Adenine and Guanine

•Pyrimidines - Small bases

–Cytosine and Thymine

–A=T and G=C

–Complementary strands

Three-Dimensional Structure of DNA

•Watson and Crick - DNA is double helix

– bases of two strands pointing inward forming base-pairs (twisted ladder)

–Purines pairing with pyrimidines.

•2 nm diameter.

•1nm = 1/1,000,000,000 m

–antiparallel.

Semi-Conservative Replication

•Double helix unzips and undergoes semi-conservative replication.

–Each ½ of the original “ladder” becomes ½ of new “ladder”.

•Replication origin = specific sequence where DNA replication begins

–DNA polymerase adds nucleotides to growing DNA strands

Replication Process

•RNA primer links first nucleotides and attaches DNA polymerase.

•DNA polymerase adds nucleotides to 3’ end.

–Leading strand replicates toward replication fork.

–Lagging strand elongates from replication fork.

•DNA ligase attaches fragment to lagging strand.

DNA Replication Fork

Replication Process

•Opening DNA Double Helix

•Building a Primer

•Assembling Complementary Strands

•Removing the Primer

•Joining Okazaki Fragments