Studied by 2 people
Watson and crick
Introduced double helical model for structure of DNA, semiconservative model, the bases pairings suggested a copy
Griffith
Genetic role was discovered, mixed heat killed with living cells of harmless strain, created transformation
Avery, McCarty and Macleod
Transforming substance was DNA, exposed that the boiled bacteria would destroy the compound, DNAase
Hershey and Chase
Showed DNA is genetic material of phage T2, only one component enters the E.coli cell, injected DNA provides genetic material
Chargaff
Reported DNA composition varies from one species to another (AT-GC)
Wilkins and Franklin
Used X-ray crystallography to study the DNA structure, produced picture of DNA
Méselos and Stahl
Experiment supported the semiconservative model, labeled nucleotides of old strands with heavy isotopes of nitrogen, first replication produced hybrid DNA, second rep produced light and hybrid, eliminating dispersive model
Transformation
A change in genotype and phenotype due to assimilation of foreign DNA
DNase
Enzyme that breaks down DNA, stopped transformation but boiled DNase did not
Semiconservative model of replication
Predicts when double helix replicates, each daughter molecule will have one old strand
Conservative model
Two parent strands rejoin
Dispersive model
Each strand is a mix of old and new
Origins of replication
Two DNA strands are separate forming a replication bubble
Eukaryotic chromosomes maybe have 100s-1000s of origins of replication
Replication direction
Proceeds in both directions from each origin, until entire molecule is copied
Replication fork
End of replication bubble, Y shaped region where new DNA strands are elongating
helicase
Enzyme that untwist double helix at replication fork
Single stranded binding proteins
Binds and stablilzes ssDNA until it can be used as a template
Topoisomere
Corrects “over twisting” and strain(straightening a twisted cord) ahead of replication forks by breaking, swiveling and rejoining DNA strands
DNA polymerase
Catalyzes elongation of new DNA at a replication fork, can only add nucleotides to 3’ end, requires a primer and DNA template strand
Primer
Initial nucleotide strand is a short RNA, later removed at replaced by DNA
Primase
Adds RNA nucleotides one at a time using parental DNA as a template,
Rate of elongation
500 nucleotides in bacteria, 50 nucleotides in human cells
Nucleoside triphosphate
Each nucleotide added to a growing DNA strand
What occurs in the exergonic reaction for energy
Sugars(dATP,dTTP,dGTP) join DNA strand and will lose phosphate groups, needed for bonding
Antiparallel structure
Two strands placed in opposite directions, affects replication
What happens in antiparallel elongation
DNA poly adds nucleotides only to a free 3’ end of a growing strand, a new dna strand can elongate only 5’ to 3’ direction
Leading strand
It moves toward the replication fork
Lagging strand
Elongate the other new strand, DNA polymerase must work in direction away from the replication fork, synthesized as a series of segments
Okazaki fragments
A series of segments that are join ed together by DNA ligase
Mismatch repair
Enzymes that correct errors in base pairs
How can DNA be damaged
By chemicals, radioactive emissions, X-rays, UV light and certain molecules
Nucleotide Excision Repair
A nucleares cuts out and replaces damaged stretches of DNA
Telomeres
Nucleotide sequences found at the ends of eukaryotic chromosomal DNA molecules, postpone erosion of genes near ends of DNA molecules
Telomerase
Enzymes that catalyzes lengthening of telemores in germ cells, shortening of cells protect cells from cancer growth
Bacterial chromosomes
Double stranded, circular DNA molecule associated with small amount of protein (found I’m nucleoid)
Chromatin
Complex DNA and protein, found in nucleus of eukaryotic cells
Histones
Responsible for first level of DNA packaging, positively charged amino acids
Nucleosomes
Beads of DNA wound around a protein core composed of 8 histone molecules
Heterochromatin
Stay condensed, found around centromeres and telomeres (not transcribed)
Euchromatin
Less condensed chromatin, may be transcibed
Nuclei acid hybridization
The base pairing of one strand of a nucleic acid to another
Genetic engineering
Direct manipulation of genes for practical purposes
Plasmids
Small circular DNA molecules that replicate separately from bacterial chromosome
Gene cloning
Using bacteria to make multiple copies of genes, foreign DNA inserted into a plasmid, and recombinant plasmid is inserted into a bacterial cell
Restriction enzymes
Cut DNA molecules at specific DNA sequences, makes many cuts like restriction fragments
Restriction fragments
Most useful restriction enzymes producing fragments with sticky ends
Sticky ends
That bond with complementary sticky ends of other fragments
DNA ligase
Enzymes that seals bonds between restriction fragments
Cloning vector
In gene cloning, a DNA molecule that can carry foreign DNA into host cell
PCR
Can produce many copies of a specific target segment of DNA, 3 step cycle brings a chain reaction that produces a growing population, need heat-stable DNA called Taq polymerase
DNA sequencing
Once a gene is cloned, complementary base pairing can be exploited to determine the gene complete nucleotide sequence, sequence by synthesizing the complementary strand of a single template strand
Cas9
nuclease that cuts double-stranded DNA molecules as directed by a guide RNA that is complementary to target gene
CAS9 system
Disable a given gene in order to determine its function, it repair a gene that has a mutation
