NOTES:NOTES: DNA Experiments & Structure

Monday 3-8-2010

(1) Griffith’s Experiment:• Question: What about a “disease” kills animals?

• Experiment:– Injected some mice w/dead bacteria– Injected some mice w/dead disease bacteria,

and living normal bacteria

• Results:– Mice w/only dead bacteria No Disease– Mice w/Mixture Disease– “Disease” carried in some molecule, which was

passed on to the living-normal bacteria!

http://www.quia.com/files/quia/users/hlrbiology/Animations/08_DNA_and_Proteins/Griffith_Mouse_Experiment.swf

(2) Hershey-Chase Experiment:• Question: Does DNA or Protein contain genetic

information?

• Experiment:– Dyed the DNA, and the protein in viruses.– Infected bacterial cells with the viruses.

• Results:– DNA ended up inside the bacteria, and made

more viruses.– Protein stayed outside the bacteria.– DNA contains genetic instructions, not protein!

• http://highered.mcgraw-hill.com/olc/dl/120076/bio21.swf

(3) Wilkins & Franklin’s Experiment:

• Question: What is the overall shape of DNA?

• Experiment:– Shot X-rays at DNA crystals– Recorded the ray-pattern

• Results:– Produced an X-Ray diffraction photograph.– Saw an uneven, X shape.– DNA is a double helix with minor and major

grooves!

(4) Watson & Crick’s Experiment:

• Question: What is the chemical structure of DNA?

• Experiment:– Pieced the DNA compounds together like a puzzle.

• Results:– Phosphate and Sugar alternate on the outside of DNA.– Nitrogenous Bases are inside the helix.– Adenine forms 2 hydrogen bonds w/Thymine.– Guanine forms 3 hydrogen bonds w/Cytosine.

(5) Nucleotide:• Nucleotide:Nucleotide: The monomer of a nucleic acid

(like DNA).

• Made Of:– 1-Phosphate– 1-Sugar– 1-Nitrogenous Base

(6) DNA Structure:• Double Stranded• Double Helix• Anti-parallel strands

• DNA Nucleotides:DNA Nucleotides:– Phosphate– Deoxyribose Sugar– Nitrogenous Bases:

• A = Adenine• T = Thymine• G = Guanine• C = Cytosine

(7) Anti-Parallel StrandsAnti = OppositeAnti = Opposite

• Strands are flip-flopped from one another

• One Strand’s 3’ End, matches the other’s 5’ End!

(8) Chargaff’s Rule:• Adenine ---- Thymine

– %A = %T

• Guanine ---- Cytosine– %G = %C

• (A+T) + (G+C) = 100%(A+T) + (G+C) = 100%– Use this to determine percentage of types of

bases.