Download DNA

DNA
Created from several
PowerPoints on the state’s
website
WHAT IS DNA?
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Deoxyribonucleic acid – DNA
Inside each of 60 trillion cells in the human body
are strands of genetic material called
chromosomes
On these chromosomes are nearly 30,000
genes
The gene is the fundamental unit of heredity. It
instructs the body cells to make proteins that
determine everything from hair color to
susceptibility to disease
More about DNA
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DNA is a polymer
Discovery of DNA
James Watson and Francis Crick – 1950s
 Deduced the structure of DNA
 Controls the genetic traits of all living cells,
plants and animals
 Four types of bases associated with DNA
 Adenine, cytosine, guanine, and thymine
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DNA is composed of two DNA stands
coiled into a double helix
 A opposite T
 G opposite C
 Known as complementary base pairing
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1985 – discovery that portions of the DNA
structure of certain genes are as unique to
each individual as fingerprints
 Alec Jeffreys and colleagues at Leicester
University named process for isolating and
reading DNA markers DNA fingerprinting
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All of the human chromosomes taken
together contain about 3 billion base pairs.
From these numbers, we can begin to
appreciate the diversity of DNA and hence
the diversity of living organism consisting
of the alphabet
 A,T,G,C
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DNA at work
Inheritable traits are controlled by DNA
arise out of its ability to direct the
production of complex molecules called
proteins.
 Proteins are made by linking a
combination of amino acids
 20 known amino acids
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Evidence for a Genetic “Factor”
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1928 – Frederick Griffith’s “Transforming
Factor” Experiment
• Conclusion: “Something” from Heat-treated
Strain 1 “transformed” Strain 2 to become deadly
DNA is Proven to be that
Genetic Factor
1944 – Oswald Avery and colleagues
focused on two of the genetic factor
candidates: protein and DNA
 Repeated Griffith’s experiment, but with a
modification
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Proteases
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DNases
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Mouse dies
Mouse lives
Conclusion – DNA is the transforming,
thus genetic material
DNA REPLICATION
DNA replication begins with the unwinding
of the DNA strands in the double helix.
 Each strand is then exposed to a
collection of free nucleotides.
 Letter by letter , the double helix is
recreated as the nucleotides are
assembled in the proper order, base
pairing
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DNA polymerases are enzymes that
assemble a new DNA strand in the proper
base sequence determined by the original
or parent DNA strand.
 PCR polymerase chain reaction – using
DNA polymerases to copy a DNA strand
located outside a living cell – new lab
technology
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Small quantities of DNA or broken pieces
of DNA found in crime-scene evidence can
be copied with the aid of a DNA
polymerase
 A DNA Thermal Cycler is used for the
copying process
 Sample size no longer a limitation in
characterizing DNA recovered from csevi
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R/ship b/t base letters on a DNA strand
and the type of protein specified for
manufacture by the sequence of these
letters is called the genetic code
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Key to understanding DNA typing lies in
the knowledge that within the world’s
population numerous possibilities exists
for the number of times a particular
sequence of base letters can repeat itself
on a DNA strand. Possibilities become
greater when one deals with two ch. Each
containing different lengths of repeat sequ.
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It’s the length differences associated with
DNA strands or RFLPs(Restriction
Fragment Length Polymorphisms) that
allow forensic scientists to distinguish one
person from another
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Once DNA molecules have been cut up by
the restriction enzyme, the resulting
fragments must be sorted out – by
electrophoresis – DNA from various
sources, cut up by restriction enzymes, is
placed in an separate lanes on an
electrophoretic gel and subjected to an
electric field
During this process, DNA fragments will
migrate across a gelcoated plate –
fragments are chemically treated so that
the strands separate from each other
 RFLP DNA typing- used in impeachment
trial of President Bill Clinton – semen
stained dress of Ms. Lewinsky pg 372
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SIGNIFICANCE
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About 25% of the DNA exams conducted
by the FBI lab since 1989 have excluded
suspects identified by police as the source
of DNA evidence collected from the crime
scene
In the Beginning…..
The world of science debated on what the
genetic material was
 Some thought it was protein
 Others believed it was DNA
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The Structure of DNA
Continued
• Phosphate Group – provides the “backbone” of
DNA 5’ end (5 prime end)
• Sugar – called a deoxyribose; also part of the DNA
“backbone” 3’ end (3 prime end)
• Backbone of DNA called the sugar-phosphate
backbone
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One of the most publicized cases
performed on human remains was the id
of the individual buried in the tomb of the
Vietnam War’s unknown soldier
Pairing of Bases
In DNA G hydrogen bonds with C
 T hydrogen bonds with A
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G
C
C
G
C
G
A
T
T
A
G
C
T A
A T
C
G
G T A T
C A T A
Were believed to belong to First Lt.
Michael J. Blassie, whose A-37 warplane
was shot down near An Loc, South
Vietnam, in 1977
 1984 – US Army Central Identification Lab
– failed to identify remains by physical
characteristics
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1998 – Blassie family, mtDNA analysis
analysis and was confirmed to be
consistent with Lt. Blassie’s family
Combined DNA Index System
CODIS
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All 50 states have legislatively mandated
the collection of DNA samples from
convicted offenders of particular crimes
and the establishment of DNA databases
for law enforcement purposes
CODIS – computer software program
developed by the FBI that maintains local,
state, and national databases of DNA
profiles from convicted offenders,
unsolved crime scene evidence, and
profiles of missing persons
 READ STORY page 390
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Luminol – can be used to locate traces of
blood and areas that have been washed
nearly free of blood without compromising
the potential for DNA typing
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READ CASE page 395
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Criminalistics Chapter 13