DNA and the CENTRAL DOGMA

Everything you never wanted to know, but still need to understand… and then some more bonus stuff to really make

you happy

Transformation of Bacteria

1928 Fredrick Griffith

a) Mouse dies b) Mouse lives c) Mouse lives d) Mouse dies. Living S cells are found in blood sample from dead mouse

Phages are viruses that infect bacteria (bacteriophage)

1. Mix phages with bacteria

2. Blend to mix

3. Centrifuge and measure radioactivity

What makes up DNA subunits?

• 5-carbon sugar

• Phosphate

• Nitrogenous base

• A and G are Purines (double rings)

• C and T are pyrimidines (single rings)

“Attorney Generals are pure”

DNA REPLICATION

2 complimentary strands. A=T C≡G

Helicase breaks H bonds and unzips

DNA polymerase attaches nucleotides to each template strand

Each “daughter” DNA consists of one parental and one new strand

Conservative – parental helix remains intact; an all new copy is made

SemiConservative – two strands separate and each functions as a template

Dispersive – each strand contains pieces of old and new DNA

Meselson-Stahl Experiment

Incorporates heavy nitrogen into DNA

Incorporates lighter nitrogen into DNA

“new” DNA synthesized would be lighter than the “old” DNA

1st replication ~20 min

2nd replication ~40 min

EUKARYOTES: many origins of replication

Incorporation of nucleotideEnzyme DNA polymerase catalyzes this reaction

5’3’ direction of one strand runs counter to the other

DNA Helicase – unzips

Topoisomerase – unwind DNA

SSBP – single strand binding proteins, hold strands open

Primase – joins RNA nucleotides to eukaryotes (primer is required for polymerase to synthesize)

DNA Polymerase – adds nucleotides

Ligase – link Okazaki fragments

New DNA

Excision repair of

DNA

FROM GENE TO PROTEINBeadle and Tatum – one gene, one polypeptide