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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 10
Molecular Biology of the Gene
Modules 10.1 – 10.5
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Saboteurs Inside Our Cells
• The invasion and damage
of cells by the herpesvirus
can be compared to the
actions of a saboteur
intent on taking over a
factory
– The herpesvirus hijacks
the host cell’s molecules
and organelles to
produce new copies of
the virus
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• Viruses provided
some of the earliest
evidence that genes
are made of DNA
• Molecular biology
studies how DNA
serves as the
molecular basis of
heredity
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In 1928, Frederick Griffith, an English army doctor, wanted
to make a vaccine against a bacteria named Streptococcus
pneumoniae, which caused a type of pneumonia. Since the
time of Pasteur, about 50 years before, vaccines had been
made using killed microorganisms which could be injected
into patients to elicit the immune response of live cells
without risk of disease. Though he failed in making the
vaccine he stumbled on a demonstration of the transmission
of genetic instructions by a process we now call the
"transformation principle".
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Experiments showed that DNA is the genetic material
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• What was the transforming principal??????
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Experiments showed that DNA is the genetic material
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• DNA was the genetic, transforming principal….
Oswald Avery: the professor, DNA, and the Nobel Prize that
eluded him.
Professor Emeritus of Pathology, Dalhousie University.
In 1944, two Canadians, Oswald Avery and Colin MacLeod, and an
American, McCarty, published a paper in The Journal of
Experimental Medicine that demonstrated genes to be the chemical,
deoxyribonucleic acid (DNA). Even though this paper is now
regarded as the single most important publication in biology of the
20th century, Avery was not awarded the Nobel Prize. This raises the
question as to why his work did not earn him the Prize. These are
several possible reasons: the discovery may have been ahead of tis
time; all three authors were physician-scientists and not recognized
chemists or geneticists; and Avery, the principal author, had reached
an advanced age and characteristically took an extremely cautious
and low-key approach to his work. Discussion of these reasons in
turn raises other issues surrounding the recognition of the work of
celebrated scientist, from Galileo and Copernicus onwards.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Experiments showed that DNA is the genetic
material
• The Hershey-Chase
experiment showed
that certain viruses
reprogram host
cells to produce
more viruses by
injecting their DNA
Head
DNA
Tail
Tail
fiber
Figure 10.1A
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• Phage reproductive cycle
Phage attaches
to bacterial cell.
Phage injects
DNA.
Phage DNA directs host
cell to make more phage
DNA and protein parts.
New phages assemble.
Cell lyses and releases
new phages.
Figure 10.1C
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• The Hershey-Chase Experiment
1
Mix radioactively
labeled phages with
bacteria. The phages
infect the bacterial
cells.
Phage
2
Agitate in a blender
to separate phages
outside the bacteria
from the cells and
their contents.
Radioactive
protein
Bacterium
3
Centrifuge the mixture
so bacteria form a
pellet at the bottom of
the test tube.
4
Empty
protein shell
Measure the
radioactivity in
the pellet and
liquid.
Radioactivity
in liquid
Phage
DNA
DNA
Batch 1
Radioactive
protein
Centrifuge
Pellet
Batch 2
Radioactive
DNA
Radioactive
DNA
Figure 10.1B
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Centrifuge
Pellet
Radioactivity
in pellet
For his fundamental contributions to molecular biology,
Hershey received the 1958 Albert Lasker Award and the
1965 Kimber Genetics Award. However, it was not until
1969 that Hershey, together with Delbrück and Luria, was
awarded the Nobel Prize for physiology or medicine.
Martha Chase was a lab assistant in the 1950’s and did not
receive the Nobel Prize for her work.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
DNA and RNA are polymers of nucleotides
• DNA is a nucleic acid, made of long chains of
nucleotides
Phosphate
group
Nitrogenous
base
Sugar
Phosphate
group
Nitrogenous base
(A, G, C, or T)
Nucleotide
Thymine (T)
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate backbone
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Figure 10.2A
• DNA has four kinds of bases, A, T, C, and G
Thymine (T)
Cytosine (C)
Pyrimidines
Adenine (A)
Guanine (G)
Purines
Figure 10.2B
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Note the designation of the Carbons as 1-5.
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10.3 DNA is a double-stranded helix
• James Watson and Francis Crick worked out
the three-dimensional structure of DNA, based
on work by Rosalind Franklin
Figure 10.3A, B
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• The structure of DNA consists of two
polynucleotide strands wrapped around each
other in a double helix
1 chocolate coat,
Blind (PRA)
Twist
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Figure 10.3C
• Hydrogen bonds between bases hold the
strands together
– Each base pairs with a complementary partner
– A pairs with T
– G pairs with C
Chargaff’s Rule
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• Three representations of DNA
Hydrogen bond
Ribbon model
Partial chemical structure
Computer model
Figure 10.3D
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Z-form
A-form
right-handed
B-form
right-handed
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left-handed
DNA REPLICATION
10.4 DNA replication depends on specific base
pairing
• In DNA replication, the strands separate
– Enzymes use each strand as a template to
assemble the new strands
A
Nucleotides
Parental molecule
of DNA
Both parental strands serve
as templates
Two identical daughter
molecules of DNA
Figure 10.4A
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• Untwisting and replication of DNA
Figure 10.4B
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10.5 DNA replication: A closer look
• DNA replication begins at specific sites
Origin of replication
Parental strand
Daughter strand
Bubble
Two daughter DNA molecules
Figure 10.5A
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Tid Bits
• 1. If multiple sites were not being replicated
simultaneously:
– Fruit fly DNA would take 16 days to replicate only 8
chromosomes
– In bacteria, 500 nucleotides are being added per
second/ eukaryotes are adding 50 nucleotides per
second.
2. Replication must take place in a 5’ to 3’ direction and
the DNA strand is antiparallel
3. Eukaryotes have directional issues and telomere
issues!!! (To be discussed soon, stay tuned)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Each strand of the
double helix is
oriented in the
opposite direction
5 end
3 end
P
P
• There is only 1 error
per billion base
pairs!!
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P
Figure 10.5B
P
P
P
• Nucleotides can only
be added to the free 3’
end of the DNA
strand.
P
P
3 end
5 end
• How DNA
daughter
strands are
synthesized
DNA polymerase
molecule
5 end
• The daughter
strands are
identical to
the parent
molecule
Daughter strand
synthesized
continuously
Parental DNA
5
3
– 5’ – 3’
direction
Daughter
strand
synthesized
in pieces
3
5
P
5
3
3
5
P
DNA ligase
Overall direction of replication
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Figure 10.5C
• The Enzymes of DNA Synthesis
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DNA polymerase I
fills in the spaces
between the Okasaki
Fragments.
DNA polymerase III
adds nucleotides to
the “free 3.”
Gyrase unwinds the
DNA by catalyzing
the formation of
negative supercoils.
Helicase separates
the strands.
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DNA polymerase II is a
prokaryotic DNA
polymerase most likely
involved in DNA repair
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The initial requirement for a free 3' hydroxyl group is fulfilled by the
RNA primers that are synthesized at the initiation sites by primase
enzymes.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• RNA is also a nucleic acid
– RNA has a slightly different sugar
– RNA has U instead of T
Nitrogenous base
(A, G, C, or U)
Phosphate
group
Uracil (U)
Sugar
(ribose)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.2C, D