Chapter 13 for AP bio

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