Basic Review of DNA

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Basic Review of DNA
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Biomolecules

• These are the molecules that make up all living
  things
• Carbohydrates
• Lipids
• Proteins-chains of amino acids
• Nucleic acids-chains of nucleotides

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Elements

• 99 of any living thing is made up of just 4
  elements.
• Carbon-C
• Hydrogen-H
• Oxygen-O
• Nitrogen-N
• Phosphorus-P

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Carbohydrates

• Sugars such as glucose and starches
• The function is to store energy
• Made up of C,H,O

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Lipids

• Fats and oils
• The functions are energy storage, insulation,
  protective cushion, and is the main component of
  cell membranes
• Made up of C, H, H

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Proteins

• Structural proteins such as keratin, enzymes like
  amylase, most hormones like insulin
• Functions include structure, growth, development,
  and metabolism
• Made of C, H, O, N

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Nucleic Acids

• DNA and RNA
• Storing hereditary information, directing the
  production of proteins.
• Made of C, H, O, N, P

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How DNA is related to traits

• DNA is protected in the nucleus of cells, it has
  the directions for making proteins
• DNA is transcribed into RNA which can go out of
  the nucleus to the ribosomes (protein factories)
• RNA is read by the ribosomes and translated into
  proteins
• Proteins determine the traits you see.

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• DNA RNA PROTEIN TRAIT
• Only 1 of the DNA leaves the nucleus of the
  cell.
• That 1 is responsible for making DNA a factor in
  Forensic testing

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Structure of DNA

• Made up of two chains of nucleotides
• Each nucleotide has 3 subunits
• Deoxyribose sugar
• Phosphate ion
• One of four bases
• Adenine
• Guanine
• Cytosine
• Thymine

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• The two chains of nucleotides come together to
  form a ladder.
• The nitrogenous bases are the rungs of the ladder
  
• Sugars and phosphates are the outsides of the
  ladder.
• Adenine bonds with Thymine (Two bonds)
• Guanine bonds with Cytosine(Three bonds)

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Recombinant DNA

• When a genetic code is identified on a strand of
  DNA as having the instructions for a certain
  protein, biologists want to use this protein for
  research and drugs.
• A recombinant DNA is a sequence of DNA that has
  been spliced at specific places to use the
  natural chemical producing abilities.

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Restriction Enzymes

• These are the enzymes that cut the recombinant
  DNA.
• They are special scissors that cut a specific
  strand of the DNA molecule when it recognizes the
  bases.
• These pieces of DNA are introduced into bacterial
  or animal cells that reproduce the protein over
  and over.

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Tandem Repeats

• This is a region of the chromosome that has
  multiple copies of a core DNA sequence that
  repeat constantly.
• More than 30 of the human genome is made up of
  these.
• Seem to have no impact on genetic function or
  appearance.

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Restriction Fragment Length Polymorphisms (RFLP)

• Different fragment lengths of base pairs that
  result from cutting a DNA molecule with
  restriction enzymes.
• All humans have the tandem repeats but the number
  of repeats differs greatly.
• The first scientifically accepted protocol for
  DNA typing in the USA

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Polymerase Chain Reaction PCR

• This is a technique to copy and multiply DNA
  strands.
• Uses a DNA polymerase to synthesize a specific
  region of DNA
• Uses temperature to break bonds and stimulate
  replication.
• Better than RFLP, extremely sensitive. Has been
  used to ID saliva on stamps, coke cans and
  envelopes.

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Short Tandem Repeats STR

• Locations on the chromosome that contain short
  sequence elements that repeat themselves within
  the DNA molecule.
• Usually only 3-7 bases. Much shorter than RFLP
  procedure.
• STRs can be found in bodies and stains that have
  been decomposed.

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STR v/s Y-chromosome STR

• Amelogenin gene- gene for tooth pulp, is shorter
  by 6 bases on X chromosome than the Y chromosome.
• Y chromosome is male specific and always paired
  with the X
• Very useful when more than one males is involved
  in assault.

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• Currently 20 different Y-STR markers have been
  id. A test kit is avail for 6 Y-STR .
• This is only from the male so when looking at a
  DNA profile it will take out lots of overlapping
  info.on the profile Ex. A rape specimen XX
  from female
• XY from 1st suspect
• XY from 2nd suspect

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Mitochondrial DNA

• Nuclear DNA is found only in nucleus and contains
  23 pairs of chromosomes
• Mitochondrial DNA- mtDNA- outside the nucleus and
  is inherited only from the mother.
• The mitochondria are responsible for supplying
  the energy of the cell.
• Each cell in our body has 100 to 1000 of
  mitochondria.

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• Used in cases where the DNA is degraded such as
  charred remains and small quantities like the
  hair shaft
• When a reference sample from a deceased or
  missing person, they can get mtDNA from any
  maternally related relative.However people with
  the same maternal linkage are indistinguishable.
• This testing is more sensitive than nuclear DNA
  but is much more costly and time consuming.
• The FBI has strict limits on the types of cases
  they will accept these samples from.

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Combined DNA index System CODIS

• Allows crime labs to compare DNA types recovered
  from crime scenes to DNA of convicted sex
  offenders and convicted criminals.
• Uses 13 standard STRs

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Collection procedures

• Biological evidence must be packaged in a paper
  bag or well ventilated box, never in an airtight
  container.
• Must be refrigerated or stored out of direct
  sunlight in a cool place, unless it is blood
  mixed with soil which must be frozen immediately

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• Must collect 7cc of whole blood for a reference
  or a buccal swab inside the mouth. To be kept
  refrigerated.
• Contamination can occur if the collector sneezes
  or coughs during the collection .

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Ways to prevent contamination

• Change gloves before each item
• Collect a control
• Pick up small items with forceps
• Each piece of evidence gets its own bag