1. Unit 4 Notes:
DNA Structure

2. (1) What is DNA?
• DNA = DeoxyriboNucleic Acid
• Stores genetic instructions for producing
proteins.
• Stored in the Nucleus of Eukaryotes.

4. (2) Overall DNA Structure
• Double stranded
• Helix
• Outside / Backbones Made Of:
– Alternating Phosphates and Sugars
• Inside / Steps Made of:
– Nitrogenous Bases

6. (Yes You Need To Draw This…)

7. (3) DNA Nucleotide
• A nucleotide is the monomer for DNA.
• Structure:
– Phosphate
– Deoxyribose Sugar
– Nitrogenous Base
• Looks Like:

8. (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.

9. ADENINE
THYMINE
GUANINE
CYTOSINE

11. (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%

12. 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%!

13. (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?

14. (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!

16. (Yes You Need To Draw This…)

17. (8) 5’ versus 3’:
• The 5’ End has the phosphate “hanging off”.
• The 3’ End has the sugar “hanging off”.
• Drawing: