Lecture Outline for March 4, 2005


Topic: discovery of DNA as the hereditary material

Chapter 2 – review DNA structure from section 2.3, Chapter12 sec 12.1, 12.2

Figures used in lecture:  12.2, 12.3, 12.7, 12.8, 12.9, 12.10

Additional resources

The DNA molecule is shaped like a twisted ladder. Click on "Animation" and Watson and Crick will explain DNA structure to you.

Watson and Crick - a discussion of their work

Rosalind Franklin

Discovery of DNA as the Genetic Material – Avery and mice, Chargaff, Watson & Crick

The Double Helix


Nucleic Acids

NOTE: This material is review.  We discussed this in lecture on January 24, 2005 and it is covered in section 2.3 of your textbook.

Define: nucleic acids, DNA, RNA, nucleotide, nitrogenous base, adenine (A), thymine (T), cytosine (C), guanine (G), uracil (U)

You should be able to:

1.  Describe the structure of a nucleotide

2.  Distinguish between a DNA nucleotide and a RNA nucleotide based on the structure of the sugar and the difference in the nitrogenous bases that are used in DNA and RNA

3.  Describe the structure of the double helix


DNA Is The Genetic Material

Early in the last century, scientists proposed that the genetic material was carried on the chromosomes.  Because chromosomes are composed of both DNA and protein, they did not know whether DNA or protein was carrying the genetic information..  A few experiments were done that confirmed that DNA is the genetic material.  These experiments include:

1.  Frederick Griffith, 1920’s

2.  Avery, MacLeod, McCarty, 1944

Define: Streptococcus pneumoniae, RNAse, DNAse, virulent, avirulent, transforming principle

You should be able to

1.  Describe the experiments performed by Griffith and by Avery et al., including;

     - exactly how they performed their experiment

     - the results of the experiment

     - the conclusion that was drawn from the results


Discovering the Structure of DNA

Define: "Chargaff's Rules", X-ray crystallography,

Scientists believed that discovering the structure of DNA would hopefully reveal how DNA performs its functions.  Clues to the structure of DNA came from several labs:

1.  Erwin Chargaff, 1950

2.  Rosalind Franklin and Maurice Wilkins, early 1950’s

3.  James Watson and Francis Crick, 1953

You should be able to

1.  Understand the research performed by each of the scientists listed above and how their research contributed to determining the structure of DNA

2.  Be able to identify which nitrogenous bases are purines and which are pyrimidines based on their general structures.

2.  Explain why a purine must form a complementary base-pair with a pyrimidine,


The Double Helix Structure

Define: deoxyribose, nitrogenous base, purine, pyrimidine, sugar-phosphate backbone, hydrogen bonding, complimentary base pairing, antiparallel, 5' end, 3'end, helix, double helix


Today’s Lecture (3-4-05)

DNA Topics we will cover:

1.  DNA is the hereditary material.

2.  DNA Structure

3.  DNA Function

              a.  DNA Replication

     b. DNA controls protein synthesis

         1) transcription         2) translation




Nucleic Acids

nucleotide structure:




comparison of DNA to RNA:








Early 1900’s

A primary question was “Is the DNA or the protein carrying the genetic information?”


Frederick Griffith, 1920’s

- Streptococcus pneumoniae

            S strain (smooth) – virulent;       R strain (rough) - avirulent

-investigating why only S strain causes pneumonia

-method of experiment:





Griffith’s conclusion:


Avery, MacLeod, McCarty  1944

-method of experiment:




Avery, MacLeod, McCarty”s conclusion:



Erwin Chargaff, 1950

-“Chargaff’s Rules”;



Rosalind Franklin, Maurice Wilkins

- early 1950’s

- X-ray crystallography



Franklin’s conclusion:





James Watson, Francis Crick   1953

-method of experiment:




Watson and Crick’s conclusion: