DNA: The Indispensable Forensic Science Tool

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DNA The Indispensable Forensic Science Tool

• Chapter 9 Based upon Concept Checklist Numbers
  1-8

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DNA Deoxyribonucleic Acid

• DNA is a polymer
• Polymers are very large molecules put together by
  linking units called monomers
• The monomers of DNA are called nucleotides.

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List and describe the components of a nucleotide.
How are nucleotides linked to form the double
helix known as DNA?

• Nucleotides of DNA consist of
• - a nitrogen-containing base (Either Adenine,
  Thymine, Cytosine, Guanine)
• - a sugar (deoxyribose)
• - a phosphate

• Nucleotides are linked together to form a double
  helix (twisted ladder)

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DNA Double Helix

• How are the nucleotides held together to
  form the double helix?
• What type of bonds hold the bases together?
• What type of bonds hold the sugar-phosphate
  back bone together?

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What is meant by complementary base pairing?

• Complementary Base Pairing means that
• Adenine always pairs with Thymine
• Guanine always pairs with Cytosine
• A T (2 bonds)
• G C (3 bonds)

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Structure of DNA Molecule

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Explain how complementary base pairing cuts down
on errors during DNA replication and the
synthesis of proteins.

• Adenine can only pair with Thymine because there
  needs to be two hydrogen bonds between A and T
• Guanine can only pair with Cytosine because there
  needs to be three hydrogen bonds between G and C
• Complementary Base pairing cuts down on errors
  because there are only two different pairs that
  will work to make the double helix.

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DNA Codes for Formation of Proteins

• The sequence of the bases within a DNA molecule
  code for proteins.
• Three consecutive bases known as a triplet code
  for an amino acid (or a punctuation mark- start
  or stop)
• There are 20 different amino acids. Each amino
  acid is coded by more than one possible triplet.
• Example proline, glutamate and alanine are all
  amino acids
• CCT proline, GAG glutamate, CGT alanine
• So the DNA strand that codes for these three
  amino acids would be CCT GAG CGT

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DNA sequence (to RNA) ? Amino Acids ? Protein
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What determines the shape and function of a
protein?

• The sequence of the amino acids in a protein
  chain determines the shape and function of the
  protein.

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Coding and Non-Coding Regions of DNA

• Portions of the DNA molecule code for proteins
  (sequence of bases in triplets correspond to
  amino acids which then get linked together)

• Portions of the DNA molecule contain Non-Coding
  Regions.
• These Non-Coding Regions contain sequences of
  bases that are repeated numerous times.
• TANDEM REPEAT region of a chromosome that
  contains multiple copies of a core DNA sequence
  arranged in a repeating fashion.

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Tandem Repeats

• More than 30 of the Human Genome is composed of
  repeating segments of DNA.
• These TANDEM REPEATS seem to act as filler or
  spacers between coding regions of DNA.
• Forensic Scientists use TANMEM REPEATS as a means
  of distinguishing one individual from another
  through DNA typing.

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What are TANDEM REPEATS and how are they useful
to the Forensic Scientist? (Short Answer Question)

• Tandem repeats are regions of a chromosome that
  contain multiple copies of a core DNA sequence
  arranged in a repeating fashion. They are useful
  to forensic scientists because they offer a means
  of distinguishing one individual from another
  through DNA typing.

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Describe the process of DNA replication. What is
the importance of DNA replication?

• DNA replication begins with the unwinding of the
  DNA strands in the double helix. The double
  helix is re-created as the nucleotides are
  assembled in the proper order (A with T and G
  with C). Two identical copies of DNA emerge from
  the process.
• ENZYMES known as DNA POLYMERASES are used to
  replicate DNA and to proof read for errors.

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What is polymerase chain reaction (PCR) and how
is it useful to forensic scientists? (Short
Answer Question)

• Polymerase chain reaction is a technique for
  replicating or copying a portion of a DNA strand
  outside a living cell. Three advantages of PCR
  are
• 1. PCR can be used with short DNA strands.
• 2. Shorter strands are more stable and less
  subject to degradation than longer strands
• 3. PCR can amplify minute quantities of DNA,
  thus overcoming the limited-sample-size problem
  often associated with crime scene evidence.

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What is recombinant DNA technology and what is
its purpose? How can recombinant DNA be used to
increase the production of insulin?

• Recombinant DNA is a process by which the DNA of
  an organism is altered by inserting into it
  fragments of DNA from another organism.
  Recombinant DNA technology is used when the gene
  for insulin production is inserted into bacteria.
  As the bacteria live and multiply, insulin is
  made.

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Recombinant DNA Technology
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Recombinant DNA Technology Enzymes

• Restriction enzymes Cut DNA into fragments by
  recognizing specific sequences.
• DNA polymerases replicate DNA outside of a living
  cell.
• DNA ligases glue portions of the DNA molecule
  together.

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Restriction Fragment Length Polymorphisms

• The TANDEM REPEATS are cut out of the DNA
  molecule by restriction enzymes.
• The DNA fragments are known as Restriction
  Fragment Length Polymorphisms.
• The restriction enzymes act as chemical scissors
  that cut DNA at specific locations.

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Electrophoresis

• Electrophoresis is a technique for separating
  molecules through their migration on a support
  medium under the influence of an electric
  potential.
• http//wps.prenhall.com/wps/media/objects/3801/389
  2550/electrophoresis.swf

• Electrophoresis is a technique for separating
  molecules through their migration on a support
  medium under the influence of an electric
  potential.
• http//wps.prenhall.com/wps/media/objects/3801/389
  2550/electrophoresis.swf

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Short Tandem Repeats (STRs)

• Short Tandem Repeats (STR) is a region on a DNA
  molecule that contains short segments of three to
  seven repeating base pairs.
• Examples TH01 A-A-T-G
• Multiplexing A technique that simultaneously
  detects more than one DNA marker in a single
  analysis.

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DNA Typing with STRs

• http//www.cstl.nist.gov/biotech/strbase/fbicore.h
  tm

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Sex Identification using STRs

• The AMELOGENIN gene is located on both the X and
  Y chromosomes. It is a gene that codes for tooth
  pulp.
• The AMELOGENIN is shorter on the X chromosome by
  six bases than on the Y chromosome. This
  differential length causes them to become
  different band amounts on electrophoresis.
• Males show 2 bands
• Females show only 1 band