Ch.12-1 Identifying the Substance of Genes DNA

POINT > Describe Griffith’s experiments with bacteria and mice POINT > Describe Avery’s experiments that identified DNA as genetic material POINT > Describe Hershey & Chase experiments with viruses

3 Key Experiments Griffith’s Bacterial Transformations Avery’s Continuation of Griffith’s Work Hershey & Chase’s Viral Isotopes

Frederick Griffith (1879 – 1941) POINT > Describe Griffith’s experiments with bacteria and mice Frederick Griffith (1879 – 1941) British scientist researching bacteria Griffith studied how bacteria cause pneumonia

POINT > Describe Griffith’s experiments with bacteria and mice He used two similar bacterial types S-strain: Smooth due to outer coating of saccharide molecules. Causes disease (virulent) R-strain: Rough – no saccharide coating. Harmless

POINT > Describe Griffith’s experiments with bacteria and mice 1. Injected each strain into mice S:Virulent… R: Harmless…

POINT > Describe Griffith’s experiments with bacteria and mice Griffith then heat-killed S-strain bacteria & injected into mice Harmless…

POINT > Describe Griffith’s experiments with bacteria and mice He then mixed living R-strain with heat-killed S-strain bacteria Virulent…

POINT > Describe Griffith’s experiments with bacteria and mice Conclusions from the experiment: 1. Some “factor” was transferred from heat-killed S-strain to living R-strain 2. “Factor” must contain information causing a transformation: changed harmless bacteria into disease-causing bacteria 3. “Factor” must be a gene, because disease-causing ability was inherited by offspring bacteria

Griffith discovered that WB CHECK: Griffith discovered that a) DNA is the genetic material b) some factor from virulent bacteria could cause disease even if the bacteria was killed c) some factor from virulent bacteria could cause harmless bacteria to become virulent d) harmless bacteria could become virulent if exposed to heat

POINT > Describe Avery’s experiments that identified DNA as genetic material Oswald Avery (1877 – 1955) Canadian biologist, used Griffith’s results as starting point Which molecule in the heat-killed bacteria was the key for transformation?

POINT > Describe Avery’s experiments that identified DNA as genetic material Heat-killed S-strain, making it harmless, and extracted the macromolecules: proteins, carbohydrates, RNA, DNA

POINT > Describe Avery’s experiments that identified DNA as genetic material Treated the extract with an enzyme that destroys proteins. Then repeated with enzymes to destroy lipids, carbs, RNA Protease (destroys protein)

POINT > Describe Avery’s experiments that identified DNA as genetic material He added treated extracts to harmless R-strain They became virulent! Protease (destroys protein) +

POINT > Describe Avery’s experiments that identified DNA as genetic material Avery repeated the experiment using an enzyme that destroys DNA DNase (destroys DNA) Harmless! +

POINT > Describe Avery’s experiments that identified DNA as genetic material Avery’s conclusions: 1. DNA was the transforming factor 2. DNA stored & transmitted the information for causing disease

WB CHECK: Avery showed that a) enzymes that destroy protein destroy the genetic material b) enzymes that destroy DNA destroy the genetic material c) carbohydrates are important in heredity d) DNA had to be the genetic material e) all of the above f) a and d g) b and d

Alfred Hershey Martha Chase (1908 – 1997, 1927 – 2003) POINT > Describe Hershey & Chase experiments with viruses Alfred Hershey Martha Chase (1908 – 1997, 1927 – 2003) American scientists Experiments with viruses provided more evidence to support Avery’s work

POINT > Describe Hershey & Chase experiments with viruses Hershey/Chase used bacteriophage: Virus that infects bacteria by attaching to surface and injecting its genetic information

POINT > Describe Hershey & Chase experiments with viruses Hershey/Chase used bacteriophage: Virus that infects bacteria by attaching to surface and injecting its genetic information Structure of a bacteriophage: DNA Protein

POINT > Describe Hershey & Chase experiments with viruses Radioactive elements can be used to trace molecules 1. Phages grown in different conditions (based on elements of macromolecules) DNA has lots of phosphorus, no sulfur  Grown in radioactive phosphorus-32 (32P) Protein has lots of sulfur, no phosphorus  Grown in radioactive sulfur-35 (35S)

POINT > Describe Hershey & Chase experiments with viruses 2. S-35-labelled phages were added to bacteria and allowed to reproduce

POINT > Describe Hershey & Chase experiments with viruses 3. Phages & bacteria were separated & analyzed to detect location of radioactivity Bacteria were not radioactive

POINT > Describe Hershey & Chase experiments with viruses 4. Repeated experiment with P-32 phages & analyzed to detect location of radioactivity Bacteria were radioactive!

POINT > Describe Hershey & Chase experiments with viruses Conclusion: DNA was genetic material found in genes of other organisms (confirming and adding to Avery’s results)

Hershey & Chase showed that WB CHECK: Hershey & Chase showed that a) bacteriophages are made of protein and DNA b) radioactive sulfur showed up in infected bacteria c) radioactive phosphorus showed up in infected bacteria d) DNA had to be the genetic material e) all of the above f) c and d g) a and d

So……. If genes are made of DNA, DNA must be able to: 1. Store information 2. Replicate (during S-phase) 3. Transmit information (via sexual & asexual reproduction)

We know DNA is a macromolecule of nucleic acid …we know its importance as the genetic material… …we know that it stores and transmits genetic information… …so what is the structure of DNA, that allows it to do these things?

Homework: Read pages 338-343!! Assess #1-3 page 343 Workbook page 202