Chapter 16

DNA & Replication

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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?

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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

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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

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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

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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?

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EXPERIMENT

Phage

DNA

Bacterial cell

Radioactive protein

Radioactive DNA

Batch 1: radioactive sulfur (35S)

Batch 2: radioactive phosphorus (32P)

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EXPERIMENT

Phage

DNA

Bacterial cell

Radioactive protein

Radioactive DNA

Batch 1: radioactive sulfur (35S)

Batch 2: radioactive phosphorus (32P)

Empty protein shell

Phage DNA

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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

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Chargaff’s Rules

In DNA:

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

Why would this be true?

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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

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DNA Replication

DNA DNA

2 strands separate, and each one is paired using complementary bases

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Themes (meh.)

Science as a process

Regulation

Interdependence in nature

Science, Technology, & Society

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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

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DNA Replication

16_05DNAandRNAStructure

16_07DNADoubleHelix

16_09Overview

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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?

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PROKARYOTE

EUKARYOTE