FINDING DNA

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FINDING DNA
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Proof of DNA as Genetic Material

• Was the genetic material protein or DNA?
• Mendel and Morgan did not know it was DNA.

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Frederick Griffith

• A medical officer was trying to find a vaccine
  against pneumococcus

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Rough and Smooth Pneumococcus
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Griffith 1920s

• Transformation

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Griffiths Conclusion

• Even though he had killed the S cells, he hadnt
  destroyed their hereditary material, which was
  the one part that caused the disease! When some
  more experiments had been done, it had been
  discovered that the harmless R cells, had used
  the information from the hereditary material of
  the dead S cells and became harmful this he
  called, hereditary transformation.

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Oswald Avery

• He had reported that DNA, not proteins (which was
  believed at the time), was the hereditary
  substance.

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Oswald Avery 1940s
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Averys Conclusion
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Bacteriophages (bacteria-eaters)

• Like bacteria, are very common in all natural
  environments and are directly related to the
  numbers of bacteria present.

Mostly made of just protein coat and DNA
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Bacteriophage Structure
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Alfred Hershey and Margaret Chase 1953

• Showed that the hereditary material in T2
  bacteriophages is DNA.

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Hershey-Chase
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Hershey-Chase

• CONCLUSION
• DNA is genetic material because    
                  (32P) nucleic acid not (35S)
  protein guides viral replication

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What is the structure of DNA?

• It is a nucleic acid
• Made of long chains of
• Nucleotides (a.k.a. polynucleotide)

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A Nucleotide

• MADE OF
• Sugar
• Phosphate
• Base

• Deoxyribose sugar
• PO4
• 4 kinds
• Adenine (A)
• Guanine (G)
• Thymine (T)
• Cytosine (C)

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DNA Nucleotide

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Nitrogenous Bases

• PURINES
• 1. Adenine (A)
• 2. Guanine (G)
• PYRIMIDINES
• 3. Thymine (T)
• 4. Cytosine (C)

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DNA Double Helix

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DNA Double Helix

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DNA backbone

• Sugar
• Phosphate

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DNA Structure

• Rungs of the Ladder
• Various orders of
• A, T, C, G
• Backbone
• Sugar and phosphates
• Alternate

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Relative Proportions () of Bases in DNA
Organisms A T G C

• Human 30.9 29.4 19.9 19.8
• Chicken 28.8 29.2 20.5 21.5
• Grasshopper 29.3 29.3 20.5 20.7 
• Sea Urchin 32.8 32.1 17.7 17.3
• Wheat 27.3 27.1 22.7 22.8
• Yeast 31.3 32.9 18.7 17.1
• E. coli 24.7 23.6 26.0 25.7

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Question

• If there is 30 Adenine, how much Cytosine is
  present?

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Answer

• There would be 20 Cytosine.
• Adenine (30) Thymine (30)
• Guanine (20) Cytosine (20)
• (50) (50)

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Chargraffs Rules

• the amount of (A)denine will always equal the
  amount of (T)hymine
• And
• the amount of
  (G)uanine will always
  equal the
  amount
  of (C)ytosine.

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DNA Structure

• NUCLEOTIDE

• POLYNUCLEOTIDE

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DNA STRUCTURE

• A-T
• C-G
• in tons of combinations
  makes our
  genetic code

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Nitrogenous Bases

• Why does A bond only with T and C only with G?
• What do you notice?

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Nitrogenous Bases

• T and C are single-ring
• Pyrimidines
• A and G are double-ring
• Purines
• A single bonds with a
• double

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What is the complementary base sequence on the
other strand of the DNA?
A T T G C C C T A A
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2 chains of nucleotides bind to form a DNA
molecule

• Hydrogen bonds form between the nitrogenous bases
  to join the 2 chains together
• The sugar and phosphate group together is known
  as the sugar-phosphate backbone

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Whats RNA?

• Ribonucleic Acid
• Three types
• mRNA
• tRNA
• rRNA

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Comparing DNA and RNA

• DNA
• Double stranded
• Sugar deoxyribose
• Bases A-T, C-G
• Larger
• Can repair itself

• RNA
• Single stranded
• Sugar ribose
• Bases A-U, C-G
• Smaller
• Cannot repair itself

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DNA
RNA
Both

• Single stranded molecule
• Contains uracil
• Contains ribose sugar
• - Found in nucleus and cytoplasm

• Made of nucleotides
• - Contain adenine, guanine and cytosine

• Double stranded molecule
• Contains Thymine
• Contains deoxyribose sugar
• - Found only in nucleus

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Pretty Similar

• Uracil

• Thymine

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The Race is On!

• To Determine the Structure of the DNA molecule.

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DNA Geek

• Linus Pauling was a Caltech chemist (USA), who in
  1951 had discovered the alpha helical nature of
  protein structure.

I remember his books Vitamin C and the Common
Cold and Cancer and Vitamin C also The Nature of
the Chemical Bond and protested nuclear testing
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DNA Geeks

• James Watson, a biologist from Indiana
  University, and Francis Crick, a physicist, were
  working at the Cavendish Lab in Cambridge,
  England on the structure of DNA

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Watson and Cricks Wire Model
DOUBLE HELIX First put the nitrogenous bases on
the outside
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DNA Geek

• Maurice Wilkins, a New Zealand physicist who had
  worked on the Manhattan Project, was the deputy
  director of the King's College biophysics lab.

Worked with Rosalind Franklin, but not nice to her
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DNA Geek

• Rosalind Franklin was an English chemist who was
  working in an X-ray crystallography lab in Paris,
  France in 1951.

FAMOUS PHOTO 51
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DNA Base Pairs

• Adenine with Thymine
• Guanine with Cytosine

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X ray Diffraction
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Franklins Suggestion
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DNA Bases
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Franklin

• Knew Watson and Cricks original model was wrong.
• She knew from her X-ray diffraction that the
  nitrogenous bases belonged on the inside.
• Died of ovarian cancer before she could earn the
  Nobel Prize.
• SHE WAS RIPPED OFF!!!!!!!!!!!!!!!!!!!!!!!!