The Discovery and
Structure of The
Genetic Material
called “DNA”
AP Biology
2006-2007
Frederick Griffith finds a “Transforming Factor”
live pathogenic
strain of bacteria
A.
mice die
live non-pathogenic heat-killed
strain of bacteria
pathogenic bacteria
B.
C.
mice live
mice live
mix heat-killed
pathogenic &
non-pathogenic
bacteria
D.
mice die
“Transformation” something in heat-killed bacteria
could
AP
Biology still transmit disease-causing properties
So what is this “transforming factor”
 Deoxyribonucleic Acid
or what we have been calling DNA
 every single organism on our planet has
its own DNA molecule
 “blueprint of life” why is it called this?

AP Biology
Franklin
Wilkins
Pauling
 Watson & Crick
Watson and Crick
APWatson
Biology
Crick

developed
double helix
model of DNA
DNA is a Nucleic Acid
• Nucleic Acids are made from Nucleotides
• A Nucleotide has three parts:
1. phosphate group
2. sugar molecule (Deoxyribose)
3. nitrogen-containing base (A,T,C,G)
You will have to
recognize nucleotide
shape on EOC!!!!!!
phosphate group
AP Biology
sugar
nitrogen-containing
base
A closer look at the different nitrogen
bases!
nucleotide – nucleotide – nucleotide – nucleotide

4 different nucleotides


A – adenine T – thymine
C – cytosine G - guanine
sugar
phosphate
AP Biology
N base
Making the DNA Molecule
 Base pairing rules:


AP Biology
adenine (A) = thymine (T) “AT”
guanine (G) = cytosine (C)
Don’t forget about the other nucleic acid
 RNA is different from DNA molecules



AP Biology
single strand of nucleotides
sugar is ribose
Thymine (T) is replaced with Uracil (U)
“DNA Replication”
How do cells make
new DNA molecules?
AP Biology
Copying DNA
Remember why DNA must be duplicated…
Cells divide so each cell
needs own copy of DNA
DNA in chromosomes
cell
nucleus
duplicated chromosomes
cell
AP Biology
nucleus
But how is DNA copied?
 Its called replication of
DNA

AP Biology
DNA unzips and each
side serves as a
template for a new
strand
DNA Replication
 Step 1: DNA Strands “unzip” at the

weak bonds between bases
Enzyme used - helicase
helicase
AP Biology
DNA Replication
Step 2: Complementary
strand is made
DNA bases
in nucleus
 Enzyme
DNA polymerase
 adds new bases

DNA
polymerase
AP Biology
DNA Replication
 Result is 2 exact copies of DNA to split
between new cells
DNA
polymerase
DNA
polymerase
AP Biology
Replication is fast and accurate.
• DNA replication starts at many points in eukaryotic
chromosomes.
• Called “replication bubbles”
AP Biology
Copying DNA
 Build daughter DNA
strand direction
opposite direction
 anti-parallel
- think divided highway
DNA
Polymerase
AP Biology
So lets sum it up
AP Biology