nucleic acids ex. deoxyribose nucleic acid (dna) ribonucleic acid (rna)
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Nucleic Acids
Ex. Deoxyribose Nucleic Acid (DNA)
Ribonucleic Acid (RNA)
Nucleic Acids
• Nucleic Acids– Informational Polymers: Code for all of the
proteins in an organism– Monomers: Nucleotides– Each Nucleotide is made up of:
1) Phosphate Group2) Pentose 5-C Sugar
– Ribose or deoxyribose
3) Nitrogenous bases– Adenine (A), Cytosine(C), Thymine (T), Guanine(G), and
Uracil (U)
Nucleic Acids• Polymers
– DNA – RNA (tRNA, mRNA,
rRNA)
• The nitrogenous bases (A, C, G, T) are what makes up the DNA “code”
• RNA codes are transcribed or made from DNA codes
• Proteins are then translated or made from RNA codes
DNADNA
RNARNA
ProteinProtein
Scientists call this Scientists call this the:the:
Central Central
DogmaDogma of of
Molecular Molecular
Biology!Biology!
How do we know that all of our genetic information
comes from DNA? (instead of protein)
• What type of experiment would you design to determine that DNA is the source of all genetic information?
Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation
• Frederick Griffiths was a bacteriologist studying pneumonia
• He discovered two types of bacteria:– Smooth colonies– Rough colonies
CONCLUSION:
The smooth colonies must carry
the disease!
Griffith’s 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!
• Griffith injected the heat-killed type and the non-deadly rough type of bacteria.
• The bacteria “transformed” itself from the heated non-deadly type to the deadly type.
Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation
Griffith’s Experiment did not prove that DNA was responsible for
transformationHow would you design an
experiment to prove that DNA was responsible for
transformation?
Avery, McCarty, and MacLeodRepeated Griffith’s Experiment
Oswald AveryOswald Avery Maclyn McCartyMaclyn McCarty Colin MacLeodColin MacLeod
They then added Heat-Killed Smooth to the non-deadly Rough Type of
Bacteria
CarbohydratesCarbohydrates LipidLipidss
ProteinProteinss
RNARNA DNADNA
To the Heat-Killed Smooth Type, To the Heat-Killed Smooth Type, they added enzymes that they added enzymes that
destroyed…destroyed…
S-Type S-Type Carbohydrates Carbohydrates
DestroyedDestroyed
S-Type S-Type Lipids Lipids
DestroyeDestroyedd
S-Type S-Type Proteins Proteins DestroyeDestroye
dd
S-Type S-Type RNA RNA
DestroyeDestroyedd
S-Type S-Type DNA DNA
DestroyeDestroyedd
Conclusion:Conclusion:
DNA was the DNA was the transforming factor!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
DNADNA
Protein coatProtein coat
moviemovie
Protein coats of bacteriophages labeled with Protein coats of bacteriophages labeled with Sulfur-35Sulfur-35
DNA of bacteriophages labeled with Phosphorus-32DNA of bacteriophages labeled with Phosphorus-32
BacteriumBacterium
BacteriumBacterium
PhagePhage
PhagePhage1.1. Hershey and Chase Hershey and Chase
mixed the mixed the radioactively-radioactively-labeled viruses labeled viruses with the bacteriawith the bacteria
The viruses infect The viruses infect the bacterial cells.the bacterial cells.
Protein coats of bacteriophages labeled with Protein coats of bacteriophages labeled with Sulfur-35Sulfur-35
DNA of bacteriophages labeled with Phosphorus-DNA of bacteriophages labeled with Phosphorus-3232
2.2. Separated the Separated the viruses from the viruses from the bacteria by bacteria by agitating the virus-agitating the virus-bacteria mixture in bacteria mixture in a blendera blender
Protein coats of bacteriophages labeled with Protein coats of bacteriophages labeled with Sulfur-35Sulfur-35
DNA of bacteriophages labeled with Phosphorus-DNA of bacteriophages labeled with Phosphorus-3232
3.3. Centrifuged the mixture so Centrifuged the mixture so that the bacteria would form a that the bacteria would form a pellet at the bottom of the test pellet at the bottom of the test tubetube
4.4. Measured the radioactivity in Measured the radioactivity in the pellet and in the liquidthe pellet and in the liquid
The Hershey-Chase results reinforced the Avery,
McCarty, and MacLeod conclusion:
DNA carries the genetic code!
However, there were still important details to
uncover…
But first, Review -- What are the
monomers of DNA?
• Composed of repeating nucleotides containing:– Deoxyribose 5-Carbon sugar– Phosphate group– Nitrogen base: (4 kinds)
Adenine (A) Thymine (T)Cytosine (C) Guanine (G)
The Race to Discover DNA’s Structure
The Race to Discover DNA’s Structure
19501950
Chargaff’s Rule: Chargaff’s Rule: Equal amounts of Equal amounts of AAdenine and denine and TThymine, and equal hymine, and equal amounts of amounts of GGuanine uanine and and CCytosineytosine
Erwin Erwin ChargaffChargaff
Why do you think Why do you think the bases match up the bases match up
this way?this way?
Adenine + Guanine = Too Adenine + Guanine = Too widewide
Thymine + Cytosine = Too NarrowThymine + Cytosine = Too Narrow
Adenine + Thymine = Perfect Fit from X-ray Adenine + Thymine = Perfect Fit from X-ray data or Cytosine + Guaninedata or Cytosine + Guanine
The Race to Discover DNA’s Structure
Maurice Maurice WilkinsWilkins
Rosalind Rosalind FranklinFranklin
X-Ray diffraction image of X-Ray diffraction image of DNA taken by Franklin in DNA taken by Franklin in
19511951
The Race to Discover DNA’s Structure
James WatsonJames Watson Francis CrickFrancis Crick
19531953
Compiled data Compiled data from previous from previous scientists to scientists to build a double-build a double-helical model of helical model of DNADNA
The Race to Discover DNA’s 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
DNA Replication
The “parent” molecule has two complementary The “parent” molecule has two complementary strands of DNA.strands of DNA.
Each is base paired by hydrogen bonding with its Each is base paired by hydrogen bonding with its specific partner:specific partner:
A with TA with T
G with CG with C
DNA Replication
An enzyme called “helicase” binds to a specific site An enzyme called “helicase” binds to a specific site on the DNA and separates the two strands.on the DNA and separates the two strands.
DNA Replication
Each parental strand now serves as a template Each parental strand now serves as a template that determines the order of the bases along a new that determines the order of the bases along a new complementary strand.complementary strand.
DNA polymerase enzyme moves down the strands, and inserts the correct base to pair with each half of DNA molecule.
DNA Replication
Another enzyme called Another enzyme called ligaseligase forms bonds forms bonds between the sugars and phosphates in the DNA between the sugars and phosphates in the DNA backbonebackbone
“Proofreading enzymes” double check the new strands, then the strands “zip up” and two new “daughter” DNA molecules are present.
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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