DNA & Replication
Bell Ringer
1. On a sheet of paper
2. Write down everything you know about DNA
-- Who discovered DNA?
-- What is the structure of DNA?
-- How does DNA differ from RNA?
The Beginnings
T. H. Morgan’s group showed that genes are located on chromosomes The two components of chromosomes—DNA and
protein— were candidates for the genetic material
The role of DNA in heredity was first discovered by studying bacteria and the viruses that infect them
The discovery of the genetic role of DNA began with research by Frederick Griffith in 1928
Griffin & Transformation
Griffin looked at bacteria & mice
Major finding = Transformation
Killed disease-causing bacteria + live, harmless bacteria Result: Live, disease-causing bacteria
Transformation – change in genotype and phenotype due to uptake of foreign DNA
Living S cells (control)
Living R cells (control)
Heat-killed S cells (control)
Mixture of heat-killed S cells and living R cells
Mouse dies
Living S cells
Healthy Mouse Healthy MouseMouse dies
Hershey & Chase
What is responsible for transformation? Dumb question now, but not so at the time Bacteriophages – viruses than infect bacteria
Consist of protein + DNA Which is the transformative agent?
EXPERIMENT
Phage
DNA
Bacterial cell
Radioactive protein
Radioactive DNA
Batch 1: radioactive sulfur (35S)
Batch 2: radioactive phosphorus (32P)
EXPERIMENT
Phage
DNA
Bacterial cell
Radioactive protein
Radioactive DNA
Batch 1: radioactive sulfur (35S)
Batch 2: radioactive phosphorus (32P)
Empty protein shell
Phage DNA
EXPERIMENT
Phage
DNA
Bacterial cell
Radioactive protein
Radioactive DNA
Batch 1: radioactive sulfur (35S)
Batch 2: radioactive phosphorus (32P)
Empty protein shell
Phage DNA
Centrifuge
Centrifuge
Pellet
Pellet (bacterial cells and contents)
Radioactivity (phage protein) in liquid
Radioactivity (phage DNA) in pellet
Chargaff’s Rules
In DNA:
[A] = [T] & [G] = [C]
Why would this be true?
Structural Model of DNA?
M. Wilkins & R. Franklin use X-ray crystallography to study molecular structure
Watson & Crick “deduced” that DNA was 2-stranded Double Helix
DNA Replication
DNA DNA
2 strands separate, and each one is paired using complementary bases
Themes (meh.)
Science as a process
Regulation
Interdependence in nature
Science, Technology, & Society
Semiconservative Replication
Each daughter molecule = 1 old strand (Conserved from parent strand) + 1 newly replicated strand Called Semiconservative Half of the strands are conserved from the parent
Competing (Incorrect models): Conservative & Dispersive
DNA Replication
16_05DNAandRNAStructure
16_07DNADoubleHelix
16_09Overview
Telomeres
Eukaryotic chromosomal DNA molecules have at their ends nucleotide sequences called telomeres
Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules
It has been proposed that the shortening of telomeres is connected to aging
Telomerase – enzyme that lengthens the telomere
Telomerase in cancerous cells?
PROKARYOTE
EUKARYOTE
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