The Structure of D.N.A.
Brain Tap
• What do we know about DNA?
D.N.A
• Deoxyribose Nucleic Acid
• Found in the nucleus of cells
• Ultimate function is to store and transmit genetic
information that tells cells which proteins to make, and
when to make them
Structure
• An Organic compound, made up of repeating subunits called
NUCLEOTIDES
• Each DNA molecule consists of two long chains of
nucleotides
• Each DNA Nucleotide has 3 parts
• Deoxyribose- 5 carbon sugar molecule
• Phosphate Group- phosphorous (P) atom, surrounded by Oxygen
•
(O)
Nitrogen-containing base- Containing Nitrogen (N) atom
• 4 different types of Nitrogen-containing bases
D.N.A Nucleotide
Nitrogenous bases
• Four Nitrogen-Containing bases found in DNA
nucleotides:
• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)
• Separated into two groups
• Purines: Adenine and Guanine
• Characterized by two rings of Carbon and Nitrogen
• Pyrimididines: Thymine and Cytosine
• Characterized by one ring of Carbon and Nitrogen
The Double Helix
• Watson and Crick (1950s)- suggested the “double helix” model for DNA,
providing explanation for how DNA can be made and how genetic info may
be stored in cell
• Alternating Deoxyribose sugar molecules and phosphate group molecules
form the backbone of to which nitrogenous bases attach (one strand of
DNA)
Double Helix
• Nitrogen bases, face towards centre of helix
• Allows one strand of DNA to face the bases on another strand
• Form Hydrogen Bonds between N-bases of other DNA strand
• Base pairing will be uniform in length as a 2-ring purine will
always match with a 1-ring pyrimidine
Complementary Base Pairing
• Notice in all the diagrams
• Guanine pairs with Cytosine, Thymine pairs with Adenine
• These pairs of bases are Complementary Base pairs
• General Rule: these base pairs will ALWAYS match up with
one another (A-T, C-G)
• C-G Form 3 Hydrogen Bonds, A-T  For 2 Hydrogen Bonds
(Fig 10.3)
Delicious D.N.A.
• DNA has made you, now it is your turn to make DNA!
• Please partner up, and follow along with your licorice lab
manual!
Next Class
• Learn How D.N.A. makes copies of its self!
• DNAs single cousin, RNA
• Transcription