Bio 122 DNA

T. H. Morgan

showed that genes are located on chromosomes, which contained DNA and proteins

Griffith (1928)

Discovered transformation by observing harmless R stains turn into S strains ones and give a mouse pneumonia.

Hershey and Chase (1952)

concluded that the genetic material of the bacteriophage was DNA, not protein.

Rosiland Franklin

Discovered the shape of DNA's backbone using x-ray crystallography.

Watson and Crick

Discovered DNA structure
Double helix, one full turn every 3.4 nm
Bases stacked .34 nm apart, 10 base pairs per turn
Room for hydrophobic nitrogenous bases in interior

nitrogenous base pairs

Purine paired with pyrimidine
Purine purine too long
Other too short

Chargaff's Rule

A\=T and C\=G
Like rope ladder
Sides, sugar- phosphate backbone
Bases joined by hydrogen bonds (A-T, 2; C-G, 3)

Model for DNA replication

Watson and Crick in 1954
Parent molecule w 2 complementary strands that separate, and makes templates for complimentary strand
Daughter strand is one parent and one daughter

origin of replication

Site where the replication of a DNA molecule begins., bacteria has one, eukaryotes multiple

replication fork

a Y-shaped point that results when the two strands of a DNA double helix separate so that the DNA molecule can be replicated

replication bubble

Segment of a DNA molecule that is unwinding and undergoing replication.

DNA polymerase

Enzyme at fork that elongates strand and adds nucleotides

nucleoside triphosphate

source of energy during polymerization of nucleotides
Has three phosphate groups and deoxyribose sugar, loses two phosphate groups

Pyrophosphate

Hydrolysis of this to two inorganic phosphate provides energy

5' group

Phosphate group bound to fifth carbon of sugar

3' group

Hydroxyl group bound to third carbon

Direction of elongation

5' to 3' end, opposite within bubble

leading strand

The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5' to 3' direction.

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. Like backstitching in sewing

DNA ligase

A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3' end of a new DNA fragment to the 5' end of a growing chain.

Primase

An enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template.

Helicase

An enzyme that untwists the double helix of DNA at the replication forks, separates two parent strands

single strand binding proteins

A protein that binds to the unpaired DNA strands during DNA replication, stabilizing them and holding them apart while they serve as templates for the synthesis of complementary strands of DNA.

DNA replication machine

proteins that participate in DNA replication form a large complex
Stationary, DNA gets reeled into machine and processed by proteins that are there

nucleotide excision repair

a nuclease cuts out and replaces damaged stretches of DNA
Ex. Covalent linking of thymine bases by UV radiation
DNA polymerase fills gap, Ligase seals the nick

nuclease

A DNA cutting enzyme that excises damaged DNA.