Download Chap 10 – DNA Structure

Chapter 10
Molecular Biology of the Gene
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
THE STRUCTURE OF THE
GENETIC MATERIAL
© 2012 Pearson Education, Inc.
Experiments showed that DNA is the genetic
material
 Requirements for the genetic material:

Must be able to code for unlimited amount of information

Must be stable

Yet able to change (everyone has a unique genetic sequence)
 Until the 1940s, the case for proteins serving as the
genetic material was stronger than the case for DNA.
– Proteins are made from 20 different amino acids.
– DNA was known to be made from just four kinds of nucleotides.
© 2012 Pearson Education, Inc.
Experiments showed that DNA is the genetic
material
 Frederick Griffith discovered that a “transforming
factor” could be transferred into a bacterial cell.
 Hershey and Chase experiment
 Only radio-labeled DNA entered bacteria cell
Animation: Hershey-Chase Experiment
Animation: Phage T2 Reproductive Cycle
© 2012 Pearson Education, Inc.
LE 16-2
Living S cells
(control)
Living R cells
(control)
Heat-killed
S cells (control)
Mixture of heat-killed
S cells and living
R cells
RESULTS
Mouse dies
Mouse healthy
Mouse healthy
Mouse dies
Living S cells
are found in
blood sample
LE 16-3
Phage
head
Tail
Tail fiber
Bacterial
cell
100 nm
DNA
Figure 10.1A
Head
Tail
Tail fiber
DNA
Radioactive Sulfur used to label protein
Phage
Empty
protein shell
Radioactive
protein
Bacterium
Phage
DNA
DNA
Batch 1:
Radioactive
protein
labeled in
yellow
The radioactivity
is in the liquid.
Centrifuge
Pellet
1
Batch 2:
Radioactive
DNA labeled
in green
2
3
4
Radioactive
DNA
Centrifuge
Pellet
Radioactive Phosphorous used to label DNA
The radioactivity
is in the pellet.
10.2 DNA and RNA are polymers of nucleotides
 DNA and RNA are nucleic acids.
 One of the two strands of DNA is a DNA
polynucleotide, a nucleotide polymer (chain).
 A nucleotide is composed of a
– nitrogenous base,
– five-carbon sugar, and
– phosphate group.
 The nucleotides are joined to one another by a
COVALENT BOND between sugar-phosphate
backbone.
Animation: DNA and RNA Structure
© 2012 Pearson Education, Inc.
Thymine (T)
Cytosine (C)
Pyrimidines
Guanine (G)
Adenine (A)
Purines
Nitrogenous base
(can be A, G, C, or T)
Thymine (T)
Phosphate
group
Sugar
(deoxyribose)
DNA nucleotide
RNA
 RNA (ribonucleic acid)
is unlike DNA in that it
– uses the sugar ribose
(instead of deoxyribose
in DNA) and
Nitrogenous base
(can be A, G, C, or U)
Phosphate
group
Uracil (U)
– RNA has the
nitrogenous base
uracil (U) instead of
thymine.
– RNA is a single, linear
strand
© 2012 Pearson Education, Inc.
Sugar
(ribose)
Figure 10.2D
Cytosine
Uracil
Adenine
Guanine
Ribose
Phosphate
The nucleotides are joined to one another by a COVALENT BOND
between sugar-phosphate backbone.
T
A
C
T
G
Sugar-phosphate
backbone
A
C
G
T
A
C
G
A
G
T
Covalent
bond
joining
nucleotides
T
C
A
C
A
C
A
A
G
T
Phosphate
group
Nitrogenous
base
Nitrogenous base
(can be A, G, C, or T)
Sugar
C
G
T
A
A DNA
double helix
DNA
nucleotide
T
Thymine (T)
T
Phosphate
group
G
G
G
G
Sugar
(deoxyribose)
DNA nucleotide
Two representations
of a DNA polynucleotide
Sugar–phosphate
backbone
Nitrogenous
bases
5 end
Thymine (T)
The nucleotides are
joined to one another by
a COVALENT BOND
between sugarphosphate backbone.
Adenine (A)
Cytosine (C)
Phosphate
Sugar (deoxyribose)
3 end
DNA nucleotide
Guanine (G)
Figure 10.3B
LE 16-6
Rosalind Franklin
Franklin’s X-ray diffraction
photograph of DNA
DNA is a double-stranded helix
 In 1953, James D. Watson and Francis Crick
deduced the secondary structure of DNA, using
– X-ray crystallography data of DNA from the work of
Rosalind Franklin and Maurice Wilkins and
– Chargaff’s observation that in DNA,
– the amount of adenine was equal to the amount of thymine
and
– the amount of guanine was equal to that of cytosine.
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Chargaff’s Rule: Equal proportion of A:T and G:C
10.3 SCIENTIFIC DISCOVERY: DNA is a
double-stranded helix
 Watson and Crick reported that DNA consisted of
two polynucleotide strands wrapped into a double
helix.
– The sugar-phosphate backbone is on the outside.
– The nitrogenous bases are perpendicular to the
backbone in the interior.
– Specific pairs of bases give the helix a uniform shape.
– A pairs with T, forming two hydrogen bonds, and
– G pairs with C, forming three hydrogen bonds.
Animation: DNA Double Helix
© 2012 Pearson Education, Inc.
Figure 10.3C
Twist
Nucleotides in opposing strands are
connected by HYDROGEN bonds
5 end
Hydrogen bond
3 end
1 nm
3.4 nm
3 end
0.34 nm
Key features of DNA structure
5 end
Partial chemical structure
Space-filling model
Notice the two nucleotide strands run anti-parallel (opposite)
of each other!
LE 16-8
Sugar
Adenine (A)
Sugar
Thymine (T)
Sugar
Sugar
Guanine (G)
Cytosine (C)