By Kristie Akl Scientists call this the: DNA l a r t
Cen f o a m RNA g o D r a
l u c Mole ! y g o Biol Protein
How do we know that all of our genetic information comes from DNA? What type of experiment would you design to determine that DNA is the source of all genetic information? Griffiths Experiment with Pneumonia and the accidental
discovery of Transformation Frederick CONCLUSION: Griffiths was a bacteriologist studying pneumonia The smooth He discovered colonies
must two carry typesthe of disease! bacteria: Smooth colonies Rough colonies Griffiths Experiment with Pneumonia and the accidental discovery of Transformation
When heat was applied to the deadly smooth type And injected into a mouse The mouse lived! Griffiths Experiment with Pneumonia and the accidental discovery of Transformation
Griffith injected the heatkilled type and the nondeadly rough type of bacteria. The bacteria transformed itself from the heated nondeadly type to the deadly type. Griffiths Experiment did not prove that DNA was responsible for transformation How would you design an experiment to prove that DNA
was responsible for transformation? Avery, McCarty, and MacLeod Repeated Griffiths Experiment Oswald Avery Maclyn McCarty Colin MacLeod
Avery, McCarty, and MacLeod Added the non-deadly Rough Type of Bacteria to the Heat-Killed Smooth Type To the Heat-Killed Smooth Type, added enzymes that destroyed Carbohydrates Lipid Protein
DNA Destroyed Destroye Destroye Destroye Destroye d d d d Conclusion: DNA was the transforming factor!
The Hershey-Chase Experiment Alfred Hershey & Martha Chase worked with a bacteriophage: A virus that invades bacteria. It consists of a DNA core and
a protein coat Protein coat DNA Protein coats of bacteriophages labeled with Sulfur-35 Phage 1. Hershey and Chase Bacterium
mixed the radioactivelylabeled viruses with the bacteria Phage Bacterium The viruses infect the bacterial cells. DNA of bacteriophages labeled with Phosphorus-32
Protein coats of bacteriophages labeled with Sulfur-35 2. Separated the viruses from the bacteria by agitating the virusbacteria mixture in a blender DNA of bacteriophages labeled with Phosphorus32 Protein coats of bacteriophages labeled with
Sulfur-35 3. Centrifuged the mixture so that the bacteria would form a pellet at the bottom of the test tube 4. Measured the radioactivity in the pellet and in the liquid DNA of bacteriophages labeled with Phosphorus32
The Hershey-Chase results reinforced the Avery, McCarty, and MacLeod conclusion: DNA carries the genetic code! However, there were still important details to uncover How did DNA: 1. Store information?
2. Duplicate itself easily? These questions would be answered by discovering DNAs structure The Race to Discover DNAs Structure The Race to Discover DNAs Structure
Linus Pauling 1940s Discovered the alpha-helical structure of proteins. The Race to Discover DNAs Structure
Erwin Chargaff 1950 Purine + Purine = Too wide Why do you think Chargaffs the basesRule: match up Equal amounts of
this way? Pyrimidine + Pyrimidine = Too ANarrow denine and Thymine, and equal amounts of Guanine Purine + Pyrimidine = Perfect Fit from X-ray The Race to Discover DNAs Structure
Maurice Wilkins X-Ray diffraction image of DNA taken by Franklin in Rosalind 1951 Franklin The Race to Discover DNAs Structure
1953 James Watson Compiled data from previous scientists to build a doublehelical model of DNA Francis Crick
The Race to Discover DNAs Structure was Over DNA is made up of: Four nucleotides: Adenine, Thymine, Guanine and Cytosine These follow the rules of base-pairing: Adenine bonds with Thymine Guanine bonds with Cytosine A sugar-phosphate backbone
DNA is arranged in an double-helix DNA Replication The double helix did explain how DNA copies itself We will study this process, DNA replication, in more detail
How does DNA replicate? Hypotheses: Conservative SemiConservative Dispersive Meselson-Stahl Experiment
1. Bacteria cultured in medium containing a heavy isotope of Meselson-Stahl Experiment 2. Bacteria transferred to a medium containing elemental Nitrogen Meselson-Stahl Experiment 3. DNA sample centrifuged after First
replication Meselson-Stahl Experiment 4. DNA sample centrifuged after Second replication DNA Replication The parent molecule has two complementary strands of DNA.
Each is base paired by hydrogen bonding with its specific partner: A with T G with C DNA Replication The first step in replication is the separation of the two strands. DNA Replication
Each parental strand now serves as a template that determines the order of the bases along a new complementary strand. DNA Replication The nucleotides are connected to form the sugarphosphate backbones of the new strands. Each daughter DNA molecule consists of one parental strand and one new strand.
The Race to Replicate DNA Two teams: A and B Individually, each team member will run to the board to add a nucleotide to the unzipped strand of DNA. The first team to finish base-pairing their DNA correctly will win the game.
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