Unit 6 Notes:
DNA Structure
(1) What is DNA?• DNA = DeoxyriboNucleic Acid
• Stores genetic instructions for producing proteins.
• Stored in the Nucleus of Eukaryotes.
(2) Overall DNA Structure• Double stranded
• Helix
• Outside / Backbones Made Of:– Alternating Phosphates and Sugars
• Inside / Steps Made of: – Nitrogenous Bases
(Yes You Need To Draw This…)
(3) DNA Nucleotide• A nucleotide is the monomer for DNA.
• Structure:– Phosphate– Deoxyribose Sugar– Nitrogenous Base
• Looks Like:
(4) Nitrogenous Bases• 4 Types of Bases:
– A = Adenine– T = Thymine– G = Guanine– C = Cytosine
• A’s and T’s bond together.
• G’s and C’s bond together.
ADENINE
THYMINE
GUANINE
CYTOSINE
(5) Chargaff’s Rule• Chargaff discovered how the bases pair
together in DNA.
• He found that:– % of A bases = % of T bases– % of G bases = % of C bases
• We can use Chargaff’s Rule to find exact concentrations of bases:
(%A + %T) + (%G + %C) = 100%
Do you see how all of the %’s of A and T
are about equal?
Do you see how all of the
%’s of G and C are about
equal?
…And that if we take %A + %T + %G + %C it equals 100%!
(6) Chargaff’s Rule Example:
Within the DNA of yeast cells, it is found that 16% of the bases are Adenine…
• What % are Thymine?
• What % are Guanine or Cytosine?
(7) Anti-Parallel Strands:• Anti-Parallel refers to the two strands in
DNA being positioned in opposite directions.
• One Strand goes 5’ 3’…and the other starts at 3’ 5’…
• The strands are upside down mirror images of one another!
(Yes You Need To Draw This…)
(8) 5’ versus 3’:• The 5’ End has the phosphate “hanging off”.
• The 3’ End has the sugar “hanging off”.
• Drawing: