AP Bio 6.1-6.2: DNA Structure and Replication

nucleotide (parts and definition)

monomor of nucleic acids

contains sugar, phosphate and nitrogeneous base

nucleic acids

DNA and RNA; contain elements PONCH

nucleotides found in RNA

A, U, C, G

nucleotides found in DNA

A, T, C, G

purines

adenine and guanine; have double ring structure

pyrimidines

cytosine, thymine, uracil; have single ring structure

complementary base pairing (Chargaff's rules)

hydrogen bonding between A and T (DNA) or A and U (RNA);

hydrogen bonding between C and G

antiparallel strands

the two backbones of DNA run in opposite directions. One runs 3' to 5' and the other runs 5' to 3'

DNA "backbone"

sugars and phosphates of different nucleotides are linked by covalent bonds (phosphodiester bonds)

Hershey-Chase Experiment

Used radioactive isotopes to label DNA and protein in viruses that infect bacteria; provided evidence that DNA is the genetic material

Helicase

An enzyme that breaks the H-bonds between the nitrogenous bases on the two strands of the DNA molecule during DNA replication. "Unzips" the strands

Topoisomerase

an enzyme that "untwists" the DNA double helix in preparation for DNA replication

Primase

an enzyme that adds a short RNA strand, a "primer" that provides a starting point for DNA synthesis. Primer strands are built in the 5' to 3' direction

DNA polymerase

an enzyme that adds new nucleotides to the growing strand during DNA replication. New strands are always built in the 5' to 3' direction

DNA ligase

an enzyme that seals up any gaps in the sugar-phosphate backbone during DNA replication

Leading strand

The strand of DNA that can be built continuously in the 5' to 3' direction (because the template strand is running 3' to 5')

Lagging strand

The strand of DNA that must be built in 5' to 3' fragments because the template strand is running 5' to 3'. Enzymes have to loop ahead and then work backward to build in the 5' to 3' direction

Okazaki fragments

short DNA fragments that are built on the "lagging" template strand. These will later be sealed together with the help of DNA ligase.