DNA Analysis
Lesson 1.2
PBS
What is DNA?
• Deoxyribonucleic Acid (DNA)
– A double-stranded, helical nucleic acid molecule capable
of replicating and determining the inherited structure of a
cell’s proteins.
• Human DNA is a unique code of over three billion base
pairs that provides a genetic blueprint of an individual.
– The fundamental building block of life.
– Hereditary material found in all living organisms.
– Found in nucleus of cells.
What is DNA?
• DNA is packaged as chromosomes, which each
contain numerous genes, or segments of DNA
sequence that code for traits.
• Chromosomes: any of the usually linear bodies in the cell
nucleus that contain the genetic material.
• Gene: a discrete unit of hereditary information consisting of
a specific nucleotide sequence in DNA (or RNA, in some
viruses).
– Consists of thousands of genes that contain
instructions for building different parts of the cell.
– Determines physical characteristics we have and some
of the diseases we will develop.
DNA Structure
• DNA from all living
organisms has the same
basic structure – the
differences are in the
sequences of the
nucleotides.
• Nucleotide
– A building block of DNA,
consisting of a five-carbon
sugar covalently bonded to a
nitrogenous base and a
phosphate group.
Pentose Sugar
• 5-Carbon sugar called
deoxyribose.
• Found on outside of
DNA molecule.
• Covalently bonded to
phosphate.
Nitrogenous Bases
• Adenine
– A component of nucleic acids, energy-carrying molecules such as ATP, and
certain coenzymes. Chemically, it is a purine base.
• Cytosine
– A component of nucleic acids that carries hereditary information in DNA and
RNA in cells. Chemically, it is a pyrimidine base.
• Guanine
– A component of nucleic acids that carries hereditary information in DNA and
RNA in cells. Chemically, it is a purine base.
• Thymine
– A component of nucleic acid that carries hereditary information in DNA in
cells. Chemically, it is a pyrimidine base.
• Base pairs found on inside of DNA molecule.
• The sequence of these bases determine an organism’s traits.
Phosphate Group
• Found on the outside of
the molecule.
• Covalently bonded to
deoxyribose sugar.
Double-Helix
• Helix: something spiral in
form.
– Antiparallel double helix.
• Chargaff’s Rules:
– Adenine binds to Thymine
• Amount of A=T
• 2 Hydrogen Bonds
– Guanine binds to Cytosine
• Amount of G=C
• 3 Hydrogen Bonds
How does DNA differ from person to
person?
• The difference between different people’s
DNA is only about 0.1%.
• The sequence of nucleotides differs from
individual to individual creating a unique DNA
profile for every person.
– Only identical twins have the same DNA profile.
How do scientists isolate DNA in order
to study it?
• DNA Extraction
– Can be isolated from plant and animal cells.
– Take advantage of unique chemical properties of the
DNA.
– Cell Components:
• Cell walls/cellulose (PLANTS ONLY)- physical action to break
down.
• Cell membranes/nuclear membranes- detergents/soaps
break down.
• Proteins- meat tenderizer breaks down.
• Ethanol removes contaminates like proteins and other
cellular components.
DNA Can Be Extracted From:
• Cells in:
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Bone
Blood
Hair Root & Shaft
Semen
Saliva
Teeth
Urine & Feces
Fingernail Debris
Muscle Tissue
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Cigarette Butts
Postage Stamps
Envelope Sealing Flaps
Dandruff
Fingerprints (Touch DNA)
Personal Items: razor
blade, chewing gum,
wrist watch, ear wax,
toothbrush.
Challenges When Extracting
• Contamination
• Degradation- heat, humidity, UV damage.
• Mixed Samples (Will show multiple profiles)
How can tools of molecular biology be
used to compare the DNA of two
individuals?
• DNA Extraction
• DNA Amplification- process called Polymerase
Chain Reaction (PCR) where multiple choices
of the DNA sample are made.
• DNA Analysis
– Restriction Enzymes
– Gel Electrophoresis
What are restriction enzymes?
• Enzymes are proteins that speed up chemical
reactions.
• Restriction Enzyme (Restriction Endonucleases):
– A degradative enzyme that recognizes specific
nucleotide sequences and cuts up DNA.
– Attaches to the DNA and reads the base sequence;
then breaks the covalent bonds between the sugar
and phosphate at the restriction site and “cuts” the
DNA into multiple pieces.
– Found in bacteria.
Restriction Enzymes: Molecular Scissors
• Cut DNA at specific
sequences
• What kinds of bonds are
broken when restriction
enzymes cut?
– Covalent bonds (within a
single strand)
– Hydrogen bonds
(between strands) as a
result of the strands
coming apart
Hydrogen
bond
Covalent bond
What are restriction fragment length
polymorphisms?
• Restriction Fragment Length Polymorphisms
(RFLPs)
– Differences in DNA sequence on homologous
chromosomes that can result in different patterns
of restriction fragment lengths (DNA segments
resulting from treatment with restriction
enzymes).
– Different segments of DNA; measured in base pair
length/number of base pairs.
– Analyzed using gel electrophoresis.
What is gel electrophoresis and how
can the results of this technique be
interpreted?
• Since the sequence of DNA is to small to see,
gel electrophoresis separates DNA fragments
based on size and electrical charge.
• Measure their rate of movement through an
electrical field in a gel.
Gel Electrophoresis
• DNA is loaded into an agarose (sugar) gel.
• An electrical current is supplied to separate
the different size DNA fragments.
• DNA has a negative charge (from the
phosphate groups) and is repelled by the
negative side of the apparatus and
attracted to the positive side.
• The DNA shows up as bands on the gel.
Smaller pieces of DNA move faster (further) because they
have less frictional resistance in the agarose.
DNA Profiles or DNA Fingerprints
DNA Profiling Uses
• Can be used to:
– Match suspect and crime scene DNA.
– Match a baby with possible fathers.
– Match bone DNA or body parts with a missing
person DNA.
– Track genealogy.
– Study bio-history (Anthropology & Archeology).
– Diagnose disease (gene therapy, genetic
counseling, genetic conditions).