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• Chapter 12~
The
Molecular
Basis of
Inheritance
12.1 The Genetic Material
• Frederick Griffith investigated virulence of
Streptococcus pneumoniae
 Concluded that virulence could be passed
from a dead strain to a nonvirulent living strain
 Transformation
• Further research by Avery et al.
 Discovered that DNA is the transforming
substance
 DNA from dead cells was being incorporated
into the genome of living cells
2
The Genetic Material
• Griffith’s Transformation Experiment
 Mice were injected with two strains of
pneumococcus: an encapsulated (S) strain
and a non-encapsulated (R) strain.
• The S strain is virulent (the mice died); it has a
mucous capsule and forms “shiny” colonies.
• The R strain is not virulent (the mice lived); it has
no capsule and forms “dull” colonies.
3
Griffith’s Transformation
Experiment
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
capsule
Injected live
R strain has
no capsule
and mice
do not die.
Injected live
S strain has
capsule and
causes mice
to die.
a.
b.
Injected heatkilled S strain
does not cause
mice to die.
c.
Injected heat-killed
S strain plus live
R strain causes
mice to die.
Live S strain is
withdrawn from
dead mice.
d.
4
Searching for Genetic
Material
• Hershey and Chase (1952)
• bacteriophages (phages)
• DNA, not protein, is the hereditary material
• Experiment: sulfur(S) is in protein,
phosphorus (P) is in DNA; only P was
found in host cell
The Genetic Material
• Transformation of organisms today:
 Result is the so-called genetically modified
organisms (GMOs)
• Invaluable tool in modern biotechnology today
• Commercial products that are currently much used
• Green fluorescent protein (GFP) can be used as a
marker
– A jellyfish gene codes for GFP
– The jellyfish gene is isolated and then transferred to a
bacterium, or the embryo of a plant, pig, or mouse.
– When this gene is transferred to another organism, the
organism glows in the dark
8
Animation
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D:\ImageLibrary1-17\16MolecularBasisInheritance\16-02PhageT2Reproduction.mov
10
The Genetic Material
• DNA contains:
 Two Nucleotides with purine bases
• Adenine (A)
• Guanine (G)
 Two Nucleotides with pyrimidine bases
• Thymine (T)
• Cytosine (C)
11
The Genetic Material
• Chargaff’s Rules:
 The amounts of A, T, G, and C in DNA:
• Are constant among members of the same species
• Vary from species to species
 In each species, there are equal amounts of:
• A and T
• G and C
 All this suggests that DNA uses
complementary base pairing to store genetic
information
 Each human chromosome contains, on
average, about 140 million base pairs
 The number of possible nucleotide sequences
is 4140,000,000
12
Nucleotide Composition of DNA
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
NH2
adenine
(A)
C
N
C
HC
C
CH
N
O
HO
P
O
O
5
4
CH2
N
C
thymine
(T)
N
O
HN
nitrogen-containing
base
CH
C
O
CH3
C
N
O
O
C H
H C
3
OH
HO
H C1
C H
2
H
P
O
C
C
HN
4
CH2
O
C H
H C1
C H
2
H
sugar = deoxyribose
NH2
N
O
HO
P
C
O
O
5
4
CH2
O
N
CH
C
CH
N
N
O
O
C H
H C
3
OH
a. Purine nucleotides
C
cytosine
(C)
N
CH
H2N C
phosphate
5
H C
3
OH
O
guanine
(G)
O
HO
H C1
C H
2
H
P
O
b. Pyrimidine nucleotides
O
5
4
CH2
O
C H
H C
3
OH
H C1
C H
2
H
DNA Composition in Various Species (%)
Species
A
T
G
C
Homo sapiens (human)
31.0
31.5
19.1
18.4
Drosophila melanogaster (fruit fly)
Zea mays (corn)
Neurospora crassa (fungus)
27.3
25.6
23.0
27.6
25.3
23.3
22.5
24.5
27.1
22.5
24.6
26.6
Escherichia coli (bacterium)
Bacillus subtilis (bacterium)
24.6
28.4
24.3
29.0
25.5
21.0
25.6
21.6
c. Chargaff’s data
13
The Genetic Material
• X-Ray diffraction:
 Rosalind Franklin studied the structure of DNA using
X-rays.
 She found that if a concentrated, viscous solution of
DNA is made, it can be separated into fibers.
 Under the right conditions, the fibers can produce an
X-ray diffraction pattern
• She produced X-ray diffraction photographs.
• This provided evidence that DNA had the following features:
– DNA is a helix.
– Some portion of the helix is repeated.
14
X-Ray Diffraction of DNA
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Rosalind Franklin
diffraction pattern
diffracted
X-rays
a.
X-ray beam
Crystalline
DNA
b.
c.
© Photo Researchers, Inc.; c: © Science Source/Photo Researchers, Inc.
15
The Genetic Material
• The Watson and Crick Model (1953)
 Double helix model is similar to a twisted ladder
• Sugar-phosphate backbones make up the sides
• Hydrogen-bonded bases make up the rungs
 Complementary base pairing ensures that a purine is
always bonded to a pyrimidine (A with T, G with C)
 Received a Nobel Prize in 1962
16
Watson and Crick Model of DNA
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
3.4 nm
0.34 nm
2 nm
b.
d.
C
a.
G
5′ end
sugar-phosphate
backbone
T
3′ end
P
A
C
G
S
P
S
A
T
P
P
T
S
3′ end
A
P
S
G
P
5′ end
C
P
complementary
base pairing
c.
C
G
P
sugar
hydrogen
bonds
a: © Photodisk Red/Getty RF; d: © A. Barrington Brown/Photo Researchers
17
Animation
Please note that due to differing
operating systems, some animations
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viewed in Presentation Mode (Slide
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All animations will appear after viewing
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18
12.2 Replication of DNA
• DNA replication is the process of copying
a DNA molecule.
• Semiconservative replication - each
strand of the original double helix (parental
molecule) serves as a template (mold or
model) for a new strand in a daughter
molecule.
19
Semiconservative Replication
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5′
3′
G
G
C
C
A
A
region of parental
DNA double helix
T
C
G
T
A
G
A
A
DNA
polymerase
enzyme
G
G
C
C
T
G
A
region of
replication:
new nucleotides
are pairing
with those of
parental strands
region of
completed
replication
new
strand
old
strand
daughter DNA double helix
5′
old
strand
3′
new
strand
daughter DNA double helix
20
Animation
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
Replication of DNA
• Replication requires the following steps:
 Unwinding, or separation of the two strands of the
parental DNA molecule
 Complementary base pairing between a new
nucleotide and a nucleotide on the template strand
 Joining of nucleotides to form the new strand
• Each daughter DNA molecule contains one old strand and one
new strand
22
DNA Replication: a closer
look
• Origin of replication (“bubbles”):
beginning of replication
• Replication fork: ‘Y’-shaped region where
new strands of DNA are elongating
• Helicase:catalyzes the untwisting of the
DNA at the replication fork
• DNA polymerase:catalyzes the elongation
of new DNA
Animation
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
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Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
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animation. Most animations will require
the latest version of the Flash Player,
which is available at
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Replication of DNA
• Eukaryotic Replication
 DNA replication begins at numerous points
along each linear chromosome
 DNA unwinds and unzips into two strands
 Each old strand of DNA serves as a template
for a new strand
 Complementary base-pairing forms a new
strand paired with each old strand
• Requires enzyme DNA polymerase
26
Replication of DNA
• Eukaryotic Replication
 Replication bubbles spread bidirectionally until
they meet
 The complementary nucleotides are joined to form
new strands. Each daughter DNA molecule
contains an old strand and a new strand.
 Replication is semiconservative:
• One original strand is conserved in each daughter
molecule, i.e., each daughter double helix has one
parental strand and one new strand.
27
Aspects of DNA Replication
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
OH
5′
P Is attached here
base is attached here
CH2
4′ C
H
O
OH
C
1′
H H
C
3′ C
OH
2′
1
H
H
De ox yrib os e m o lec u le
2
DNA polymerase
attaches a new
nucleotide to the
3 ′ carbon of the
previous nucleotide.
5′ end
P
P
P
P
G
C
C
G
3′ e nd
P
P
5′
P
T
A
P
C
G
3 ′end
P
P
5′ end
template strand
3′
template
strand
P
new strand
lagging
strand
DNA polymerase
leading
new strand
3′
Direction of replication
5
4
3
helicase at replication fork
RNA primer
template
strand
6
Okazaki fragment
3′
5′
5′
parental DNA helix
7
DNA ligase
3′
Replication fork introduces complications
DNA polymerase
28
Replication of DNA
• Accuracy of Replication
 DNA polymerase is very accurate, yet makes
a mistake about once per 100,000 base pairs.
• Capable of identifying and correcting errors
29
DNA Replication, II
• Antiparallel nature:
sugar/phosphate backbone runs in
opposite directions (Crick);
• one strand runs 5’ to 3’, while the other
runs 3’ to 5’;
• DNA polymerase only adds nucleotides
at the free 3’ end, forming new DNA
strands in the 5’ to 3’ direction only
Figure 16.12 The two strands of DNA are antiparallel
DNA Replication, III
• Leading strand: synthesis toward the
replication fork (only in a 5’ to 3’ direction
from the 3’ to 5’ master strand)
• Lagging strand: synthesis away from the
replication fork (Okazaki fragments); joined
by DNA ligase (must wait for 3’ end to
open; again in a 5’ to 3’ direction)
• Initiation: Primer (short RNA
sequence~w/primase enzyme), begins the
replication process
DNA Replication: the leading and
lagging strand
D:\ImageLibrary1-17\16MolecularBasisInheritance
\16-13LeadingStndNarrAnim_S.
mov
D:\ImageLibrary117\16MolecularBasisInherita
nce\16-13LaggingStrandAnim_B.
mov
Figure 16.15 The main proteins of DNA replication and their functions
DNA Repair
• Mismatch repair:
DNA polymerase
• Excision repair:
Nuclease
• Telomere ends:
telomerase
Figure 16.17 Nucleotide excision repair of DNA damage
Figure 16.18 The end-replication problem
Figure 16.17 Nucleotide excision repair of DNA damage
Figure 16.19b Telomeres and telomerase
Chromosomal errors, I
• Nondisjunction: members of a pair of
homologous chromosomes do not separate
properly during meiosis I or sister chromatids fail
to separate during meiosis II
• Aneuploidy: chromosome number is abnormal
 Monosomy ~ missing chromosome
 Trisomy ~ extra chromosome (Down
syndrome)
 Polyploidy~ extra sets of chromosomes
Figure 15.11 Meiotic nondisjunction
Chromosomal errors, II
• Alterations of chromosomal structure:
• Deletion: removal of a chromosomal segment
• Duplication: repeats a chromosomal segment
• Inversion: segment reversal in a chromosome
• Translocation: movement of a chromosomal
segment to another
Figure 15.13 Alterations of chromosome structure
Figure 15.14 Down syndrome
Figure 15.x2 Klinefelter syndrome
Figure 15.x3 XYY karyotype
Chromosomal Disorders
•Down syndrome
•XXY Klinefelter syndrome
•XYY
•XXX
•XO Turner syndrome
Extranuclear Genes
•Not all genes are located on the nuclear
chromosomes. These genes do not exhibit
Mendelian genetics.
•Mitochondrial DNA which is given from the
mother only, can in some rare cases cause
some disorders. If the Mitochondrial DNA is
defected this would reduce the amount of
ATP made.