Unit 4 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• The sequence of these bases ARE your genetic

code/instructions.

• 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.

• The strands are upside down mirror images of one another!