Deoxyribonucleic Acid
Organic Molecule
Contains Carbon
Nucleic Acid
Made of Nucleotides
Contains Deoxyribose
Carries Genetic Information
Individual Characteristic
Nucleotides
Monomer of nucleic acids
Phosphate Group
+
5‐Carbon Sugar
(Deoxyribose)
+
Nitrogenous Base
(A, T, C & G)
Nitrogenous Bases
Double Ringed
Single Ringed
Pyrimidines complement Purines
Sequence of bases is individual to each person
Complementary Pairs
1950: Erwin Chargaff discovered the percentage of guanine and cytosine are almost equal in any sample of DNA (the same is true of adenine and thymine).
He concluded C = G and A = T.
James Watson and Francis Crick used this information in constructing their DNA model.
Structure
Avoid Contamination
1.
2.
3.
4.
5.
Wear gloves (change often)
Use disposable instruments for each sample
Avoid touching areas you think there could be DNA
Avoid talking/sneezing/coughing over evidence
Avoid touching your face/nose/mouth when collecting/packaging evidence
6. Air‐dry thoroughly before packaging
•
Moisture  Mold  Destruction
7. Put in new paper bags/envelopes
•
No plastic!
8. If you can’t dry it, freeze it
•
No direct sunlight or heat!
Uses of DNA
• Crime scene DNA matching with suspect’s DNA
• Paternity/Maternity determination
• Identification of family members and relatives
• Suspect elimination
• Freeing those who have been falsely accused and imprisoned
• Identification of human remains
Steps Prior to Analysis
1. DNA is extracted from cells
2. DNA is cut by restriction enzymes
3. Specific DNA fragments are amplified using PCR
4. DNA fragments are separated by size during electrophoresis
DNA Fingerprinting
Forensic Scientists use short segments of DNA for comparison
Able to determine whether two DNA samples are from the same person, related people, or non‐related people
Combined DNA Index System (CODIS) is the USA’s DNA profile database