Replication

Leading strand

synthesized continuously

lagging strand

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' to 3' direction away from the replication fork.

DNA Polymerase III

In charge of synthesizing nucleotides onto the leading end in the classic 5' to 3' direction.

DNA Ligase

an enzyme that eventually joins the sugar-phosphate backbones of the Okazaki fragments

DNA Polymerase I

removes the RNA primer and replaces it with DNA

Telomeres

DNA at the tips of chromosomes

Telomerase

An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells.

Primer

a short stretch of RNA that tells DNA Polymerase III where to start replication

Helicase

unwinds DNA

Topoisomerase

corrects "overwinding" ahead of replication forks by breaking, swiveling, and rejoining DNA strands

Okazaki fragments

segments of the lagging strand

Mismatch repair

repair enzymes correct errors in base pairing

Euchromatin

a region of DNA that is uncoiled and undergoing active transcription into RNA

Heterochromatin

DNA that is densely packed around histones. The genes in heterochromatin are generally inaccessible to enzymes and are turned off.

nuclease

A DNA cutting enzyme that excises damaged DNA.

nucleotide excision repair

a nuclease cuts out and replaces damaged stretches of DNA

semiconservative replication

each new DNA molecule consists of one new strand and one old strand

Base pair rules

A pairs with T

C pairs with G

Hershey and Chase

Used radioactive material to label DNA and protein; infected bacteria passed on DNA; helped prove that DNA is genetic material not proteins

Frederick Griffith

Discovered transformation in pneumonia-causing bacteria.

Chagraff's rule

A=T and C=G

Rosalind Franklin

Used X-ray diffraction to discover the double-helical structure of DNA.