– “Informational Polymers”: Code for all of the proteins in an organism
– Polymer: Nucleic Acid
• Monomers: Nucleotides
– Each Nucleotide is made up of:
1) Phosphate Group
2) Pentose 5-C Sugar
» Ribose or deoxyribose
3) Nitrogenous bases
» Adenine (A), Cytosine(C), Thymine (T), Guanine(G), and
Uracil (U)

• Polymers
– DNA
– RNA (tRNA, mRNA, rRNA)
• The nitrogenous bases (A,
C, G, T) are what makes up the DNA “code”
• RNA codes are transcribed or made from DNA codes
• Proteins are then translated or made from RNA codes

Scientists call this the:

How do we know that all of our genetic information comes from
DNA? (instead of protein)
• What type of experiment would you design to determine that DNA is the source of all genetic information?

Griffith’s Experiment with Pneumonia and the accidental discovery of
Transformation
CONCLUSION: bacteriologist studying
The smooth colonies
• He discovered two types of bacteria:
– Smooth colonies
– Rough colonies

Griffith’s Experiment with Pneumonia and the accidental discovery of
Transformation
• When heat was applied to the deadly smooth type…
• And injected into a mouse…
• The mouse lived!

Griffith’s Experiment with Pneumonia and the accidental discovery of
Transformation
• Griffith injected the heat-killed type and the non-deadly rough type of bacteria.
• The bacteria “transformed” itself from the heated non-deadly type to the deadly type.

Griffith’s Experiment did not prove that
DNA was responsible for transformation
How would you design an experiment to prove that DNA was responsible for transformation?

Avery, McCarty, and MacLeod
Repeated Griffith’s Experiment
Oswald Avery Maclyn McCarty Colin MacLeod

They then added Heat-Killed Smooth to the non-deadly Rough Type of Bacteria
To the Heat-Killed Smooth Type, they added enzymes that destroyed…
Carbohydrates Lipids Proteins RNA DNA

S-Type
Carbohydrates
Destroyed
S-Type
Lipids
Destroyed
S-Type
Proteins
Destroyed
S-Type
RNA
Destroyed
S-Type
DNA
Destroyed

The Hershey-Chase Experiment
Protein coat
Alfred Hershey &
Martha Chase worked with a bacteriophage:
A virus that invades bacteria.
It consists of a
DNA core and a protein coat movie
DNA

Protein coats of bacteriophages labeled with Sulfur-35
Phage
Bacterium
1. Hershey and Chase mixed the radioactively-labeled viruses with the bacteria
Bacterium
Phage The viruses infect the bacterial cells.
DNA of bacteriophages labeled with Phosphorus-32

Protein coats of bacteriophages labeled with Sulfur-35
2. Separated the viruses from the bacteria by agitating the virusbacteria mixture in a blender
DNA of bacteriophages labeled with Phosphorus-32

Protein coats of bacteriophages labeled with Sulfur-35
3. Centrifuged the mixture so that the bacteria would form a pellet at the bottom of the test tube
4. Measured the radioactivity in the pellet and in the liquid
DNA of bacteriophages labeled with Phosphorus-32

The Hershey-Chase results reinforced the Avery, McCarty, and MacLeod conclusion:
However, there were still important details to uncover…

But first, Review --
What are the monomers of DNA?
• Composed of repeating nucleotides containing:
– Deoxyribose 5-Carbon sugar
– Phosphate group
– Nitrogen base: (4 kinds)
Adenine (A) Thymine (T)
Cytosine (C) Guanine (G)

The Race to Discover DNA’s
Structure

The Race to Discover DNA’s
Structure
In the 1940’s, Linus Pauling discovered the alpha-helical structure of proteins.

The Race to Discover DNA’s
Structure
Erwin Chargaff
1950 Adenine + Guanine = Too wide
Why do you think the bases match up this way?
Adenine and Thymine, and equal amounts of
Adenine + Thymine Perfect Fit
Cytosine + Guanine
Guanine and Cytosine

The Race to Discover DNA’s
Structure
Maurice Wilkins
X-Ray diffraction image of DNA taken by Franklin in 1951 Rosalind Franklin

The Race to Discover DNA’s
Structure
James Watson
1953
Compiled data from previous scientists to build a double-helical model of DNA
Francis Crick

The Race to Discover DNA’s
Structure was Over
• DNA is made up of :
– Four nitrogenous bases: Adenine, Thymine, Guanine and Cytosine
– These follow the rules of base-pairing
• Purines bond with
Purines
– Adenine bonds with Thymine
– Guanine bonds with Cytosine
– A sugar-phosphate backbone
Pyrimidines
• A sugar-phosphate backbone plus one nitrogenous base is called a nucleotide .
• DNA is arranged in a double-helix, made up of nucleotide monomers.

a. Double helix
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5' end
P
S
P
S
S
S
3' end
P
P phosphate pyrimidine base purine base
P
3' end
P
S
P
P
S
S
3' end b. Ladder structure
S
S
S
P
P
P
5' end
5' end
4'
P
5'
S
3' 2'
1'
C
5'
O
4' C
S
C 1'
C C
2' deoxyribose c. One pair of bases
1'
2' 3'
S
4'
5'
P