Download DNA: the thread of life

DNA: the thread of life
Lectured by
Chompunuch Virunanon
This presentation Partial Fulfillment of the Requirements
for the 2303107 General Biology teaching, Department of Biology
Chulalongkorn University
Academic Year 2011
Thread of Life" -Mendel's Gene Theory
Explained.
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1
What are genes?
Deoxyribonucleic acid
• Deoxyribonucleic acid or DNA, is the
genetic material that provides the blueprint
to produce an individual traits.
• Each person’s DNA id distinct and unique.
Even identical twins shows minor
difference in their DNA sequence.
• Likewise, genetics techniques have many
important application in biotechnology, are
used in criminal justices, forensic, to
provide evidence of guilt or innocent.
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What are SNPs?
DNA: genetic material
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Griffith’s experiment explanation:
bacerial transformation experiments indicated the existence of biochemical
genetic material
• In 1920, English microbiologist’
Frederick Griffith, studied a
type of bacterium known than
Pneumococci and now
classified as Streptococcus
pneumoniae.
• Some strains of S.
pneumoniae secrete
polysaccharide capsule, while
other strains do not.
S. pneumoniae
Griffith’s experiments that showed the transformation of bacteria
by a “transformation principle”
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The Avery, MacLeod and McCarty
experiment
Biochemical identification of genetic
material
1. Information: The genetic material must contain the information
necessary to construct an entire organism
2. Replication: The genetic material must be accurately copied.
3. Transmission: After it replicated, the genetic material can be passes
from parent to offspring. It also must pass from cell to cell during the
process cell division.
4. Variation: difference in genetic material must account for variation
within each species and among different species.
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• Eight years after the famous Avery, MacLeod, and
McCarty experiment was published, two scientists
named Alfred Hershey and Martha Chase performed an
entirely different type of genetic experiment.
• For their experimental system, they selected an
extremely small virus called a bacteriophage (or just
phage), which only infects bacterial cells. At that time,
scientists knew that when these phage infect a bacterial
cell, they somehow “reprogram” the bacterium to
transform itself into a factory for producing more phage.
• They also knew that the phage itself does not enter the
bacterium during an infection. Rather, a small amount of
material is injected into the bacteria and this material
must contain all of the information necessary to build
more phages. Thus, this injected substance is the
genetic material of the phage
T2 bacteriophage
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Left. Electron Micrograph of bacteriophage T4. Right. Model of phage T4. The phage possesses a
genome of linear ds DNA contained within an icosahedral head. The tail consists of a hollow core
through which the DNA is injected into the host cell. The tail fibers are involved with recognition of
specific viral "receptors" on the bacterial cell surface.
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Nucleotides contain a phosphate, a
sugar and base
DNA
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RNA
8
Levels of DNA structure to create a chromosome
Where’s DNA locate in cell?
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The structural characteristics of
prokaryotic and viral chromosome
• An early prediction was that, when DNA isolated
from a bacterial or virus is centrifuged, all of the
DNA would sediment at the same rate, forming a
band in centrifuge tube at the end of the
experiment.
• However, in 1963, Jerome Vinograd obtained an
unexpected results.
• When he centrifuged circular DNA from Polyoma
virus, two band were observed.
The structural characteristics of
prokaryotic and eukaryotic
chromosome
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Prokaryote cell
DNA organization
• DNA Organization In prokaryotes
• DNA Organization In eukaryotes
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The structural characteristics of
prokaryotic chromosome
• Bacterial chromosome
Electron micrographs of plasmid DNA (relaxed nonsupercoiled
DNA)
Bacterial
chromosome
• We learned that
the DNA of the
bacterium
Escherichia coli is
located in a central
region called the
nucleoid.
• If an E. coli cell is
lysed gently, the
DNA is released in
a highly folded
state.
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DNA Supercoiling
• 1963 observation that polyoma virus DNA
preparations had 3 different “types” of DNA
which had uniquely different sedimentation
velocities
• 1965, two are circular, one linear
– One circular molecule is “underwound”
• Negatively supercoiled (more than 10.4 bp/turn of
helix)
• Topoisomers
– Created by topoisomerases
• Types I and II
• His investigations of
this finding led to an
understanding that
circular DNA can
exist in a relaxed or
supercoiled form.
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DNA Organization In Eukaryotes
• DNA protein complex called chromatin
– Human chromosomes about 19,000 to 73,000
microns in length, total about 2 meters/cell
– Nucleus about 5-10 microns in diameter
– Condensation about 10,000X
A Microscopists' View of
Chromosome Organization
Heterochromatin
This is the condensed form of chromatin organization. It is seen as dense patches of
chromatin. Sometimes it lines the nuclear membrane, however, it is broken by clear
areas at the pores so that transport is allowed. Sometimes, the heterochromatin forms
a "cartwheel" pattern. Abundant heterochromatin is seen in resting, or reserve cells
such as small lymphocytes (memory cells) waiting for exposure to a foreign antigen.
Heterochromatin is considered transcriptionally inactive. See Alberts et al, Molecular
Biology of the Cell, Garland Publishing, 1994, pages 352 and 353
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• An important issue in transcription is
identifying the right gene
• Different type of gene
– Housekeeping genes: encode proteins that
are used all the time
– Other genes are activated only under certain
cercumstances
• eg. lactose operon of Escherichia coli
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Euchromatin
• Euchromatin is
threadlike, delicate. It is
most abundant in active,
transcribing cells. Thus,
the presence of
euchromatin is
significant because the
regions of DNA to be
transcribed or duplicated
must uncoil before the
genetic code can be
read.
Chromatin Structure
• Chromatin proteins subdivided into histones
and nonhistones
• Histones
– Very high contents of lysine + arginine (20-30%)
– Amino acid sequences very conserved between
species
• Histone IV differs by one amino acid between pea and
cow
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Chromatin in
metaphase
The first level of organization you see is a tangle of
20-30 nm fibers. These are actually coils of the DNA
and histones. The figure on the left shows the
tangled chromatin fibers in the left panel. Shearing
forces can be used to further uncoil and stretch
these fibers and the beaded filaments appear. The
strands between the beads are segments of double
stranded DNA.
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DNA Condensation
• DNA duplex 2 nm in diameter
• Nucleosome string about 11 nm in diameter
• Nucleosomes form coiled solenoid-shaped fiber
with 6 nucleosomes per spiral
– 30 nm fiber
• 30 nm fiber then folded/looped to form 300 nm
fiber
• 300 nm fibers coiled/folded to form 700 nm fiber
that forms chromatid in meiosis/mitosis
Levels of DNA
Condensation
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How DNA and Histones are
organized in chromosomes.
How can DNA duplicate itself?
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19
An overview of DNA replication
• Meselson and Stahl use density of measurement to in
vestigate mechanism of DNA replication
Three propose mechanisms for
DNA replication
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DNA replication
How gene express?
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The central dogma of molecular biology
• Protein include enzymes that catalyze
reaction use to make energy
• Proteins control cellular processes like
replication
• Protein provide channels in the membrane
for cell to communicate with each other
share metabolites
The central dogma
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Molecular gene expression in
prokaryote Vs eukaryote
• prokaryote
Molecular gene expression in
prokaryote Vs eukaryote
• eukaryote
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How can genetic material transfer
from parent to offspring ?
Thread of Life" -Mendel's Gene Theory
Explained.
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24
Mendel’s law
1. Law of Segregation (The
"First Law")
The Law of Segregation states that
when any individual produces
gametes, the copies of a gene
separate so that each gamete
receives only one copy. A gamete
will receive one allele or the other.
2. Law of Independent
Assortment (The "Second Law")
The
Law
of
Independent
Assortment,
also
known
as
"Inheritance Law" states that alleles
of
different
genes
assort
independently of one another
during gamete formation. While
Mendel's experiments with mixing
one trait always resulted in a 3:1
ratio
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Pedigree
Autosomal dominant
or recessive????
Pedigree analysis
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Genetic Technology
The first cloned pet:
In 2002 is cat!, called
CC (for carbon copy)
Gene cloning is done to achieve
one main goal
• Producing large amount of DNA or specific
gene
• Expressing the cloned gene to produce
the encoded protein
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Gene cloning
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