Biology 212 General Genetics
Lecture 1 "DNA"
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Spring 2007
Introductions
Class Roster
Handout: Course syllabus
Review of syllabus: content
 Main topics: Classical (Mendelian) Genetics, Molecular Genetics, Human
Genetics, Population Genetics
Genetics: The study of genes, the individual units of heredity
Genes: Segments of DNA that contain the information for a protein or RNA product
Molecular genetics vs. classical genetics
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Molecular genetics examines the chemical nature of genes.
o The molecule DNA contains information for our traits.
Classical or Mendelian genetics is based on the experiments of Gregor Mendel
(1860's) with the garden pea
o Developed concept that heredity is determined by discrete units
o Traits can be dominant or recessive
Human genetics: Examined through pedigree analysis (genetic family trees), karyotype
(chromosome) analysis, human genome project, DNA testing
Population genetics: Inheritance in groups of interbreeding organisms. Relevant for
conservation biology, forensics.
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Review of syllabus course requirements
 Course objectives
 Textbook
 Problem assignments
 Grading
Reading: Text Chapter 1 pp. 2-9
Lecture Outline:
1. DNA is the genetic material
a. Transformation experiments
b. Phage experiments
2. Chemical structure of DNA
3. DNA structure suits its function
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Lecture Notes:
1. DNA is the molecule of heredity: Experimental evidence
1869 Friedrich Miescher
o discovered DNA (deoxyribonucleic acid)
o DNA is abundant in cell nuclei
o DNA is a weak acid
Late nineteenth century
o Male and female reproductive cells fuse in fertilization
o Discovery of chromosomes
o Chromosomes are closely associated with DNA
1928 Frederick Griffith
o Demonstrated bacterial transformation; bacteria can be converted from a nonvirulent to a virulent strain by injection of a substance.
Fig. 1.2
S=smooth strain, causes pneumonia in mouse
R=rough strain, non-virulent
Heat-killed S cells + living R cells  inject into mouse; causes pneumonia
1944 Oswald Avery, Colin Macleod, Maclyn McCarty
o Showed that the transforming substance was DNA.
Fig. 1.3
DNA from S cells + R cells  produce S cells
Therefore the substance responsible for genetic transformation is DNA.
DNA is the genetic material.
1952 Alfred Hershey, Martha Chase
o Demonstrated that transmission of information from one generation to another
relies on DNA.
Viruses:
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Structure
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o DNA or RNA (genetic material)
o Protein coat and tail fibers
Parasites that require host cell to reproduce
Fig. 1. 4 The Hershey-Chase Experiment
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T2 virus is a bacteriophage, virus that infects bacteria
Can "tag" DNA or protein parts of T2 virus
Tag DNA of virus with radioactive phosphorus
Infect E. coli bacteria with tagged virus particles
Allow reproduction of virus and lysis of bacteria
Results:
 The bacteria release progeny viruses tagged on their DNA.
 When viral proteins were similarly tagged, the released progeny viruses do not
have tagged proteins.
2. The chemical structure of DNA
Could the molecular structure of DNA help answer
 How genetic material is duplicated?
 How DNA controls traits?
 What happens when a mutation occurs on the DNA?
1953 James Watson, Francis Crick
o Developed a 3D-structural model of DNA structure, the "DNA double helix".
Critical features of the model:
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DNA is made of nucleotides
o Sugar
o Phosphate
o Nitrogenous bases (Fig. 6.2)
 A=adenine
 C=cytosine
 G=guanine
 T=thymine
Nucleotides are linked together in long chains (Fig. 6.4)
Sugars and phosphates form the backbone
Bases occur in the interior
Bases form hydrogen bonds
o A pairs with T
o C pairs with G
The bases that pair are said to be complementary
The order of the bases on DNA comprises the information
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Two strands of DNA are antiparallel  the chains point in opposite directions
5' 3'
The two paired strands coil around each other in a double helix
3. Knowledge of the structure of DNA helps understand its function
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Each strand provides information for synthesis of a complementary strand.
DNA contains information as a linear code: the order of the bases.
Changes in the DNA (mutations) can occur from errors in copying.
DNA Replication
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Process of copying the DNA. Each parental DNA strand directs the synthesis of a
new partner strand.
DNA synthesis carried out by enzyme, DNA polymerase
Fig. 1.7
Parental DNA=template
5' A T G C C G T A 3'
3' T A C G G C A T 5'
daughter DNAs 5' A T G C C G T A 3'
3' T A C G G C A T 5'
5' A T G C C G T A 3'
3' T A C G G C A T 5'
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