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Chapter 16. 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.

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chapter 16

Chapter 16

DNA & Replication

bell ringer
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
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 & 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
slide6

Mixture of heat-killed S cells and living R cells

Heat-killed S cells (control)

Living S cells (control)

Living R cells (control)

Living S cells

Healthy Mouse

Healthy Mouse

Mouse dies

Mouse dies

hershey chase
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?
slide8

EXPERIMENT

Radioactive protein

Phage

Bacterial cell

DNA

Batch 1: radioactive sulfur (35S)

Radioactive DNA

Batch 2: radioactive phosphorus (32P)

slide9

EXPERIMENT

Empty protein shell

Radioactive protein

Phage

Bacterial cell

DNA

Batch 1: radioactive sulfur (35S)

Phage DNA

Radioactive DNA

Batch 2: radioactive phosphorus (32P)

slide10

EXPERIMENT

Empty protein shell

Radioactivity (phage protein) in liquid

Radioactive protein

Phage

Bacterial cell

DNA

Batch 1: radioactive sulfur (35S)

Phage DNA

Centrifuge

Pellet (bacterial cells and contents)

Radioactive DNA

Batch 2: radioactive phosphorus (32P)

Centrifuge

Radioactivity (phage DNA) in pellet

Pellet

chargaff s rules
Chargaff’s Rules

In DNA:

[A] = [T] & [G] = [C]

  • Why would this be true?
structural model of dna
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 Replication
  • DNA  DNA
  • 2 strands separate, and each one is paired using complementary bases
themes meh
Themes (meh.)
  • Science as a process
  • Regulation
  • Interdependence in nature
  • Science, Technology, & Society
semiconservative replication
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 replication1
DNA Replication
  • 16_05DNAandRNAStructure
  • 16_07DNADoubleHelix
  • 16_09Overview
telomeres
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?
slide24

PROKARYOTE

EUKARYOTE

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