unit 5-concept 1 the dna discovery
TRANSCRIPT
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THE DNA DISCOVERY
Unit 5- Concept 1
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Inheritance has always puzzled people
� No one really knew how it worked
� Mendel wasn’t known till the late 1800’s
� He didn’t even know what chromosomes were!
� DNA was discovered in 1869
� No one was sure what it did
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By the early 1900’s …
� This is all we knew about inheritance
� Traits are passed from parent to offspring
� Heredity of traits can be predicted
� From Mendel
� Genes are found on chromosomes
� From Morgan
� But we still did not know what the molecule of heredity was
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Chromosomes
� Scientists had discovered that the chromosomes were made of 2 materials
� DNA
� Protein
� One of them had to be the genetic material
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The case for proteins
� Most scientists thought that protein was the genetic material because it was complex
� Lots of shapes
� No one really knew much about DNA
� Components of nucleotides had been discovered
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Important Scientist People
� Each one of these scientists helped provide evidence to confirm that DNA was the genetic material
� Griffith
� Avery/McCarty/MacLeod
� Hershey/Chase
� Franklin/Wilkins
� Watson/Crick
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Important Scientist People
� What did they do that was important with the study of DNA?
� Pretend to be a scientist
� What were you researching?
� What did you find?
� How did your research contribute to the overall discovery of DNA as the genetic material?
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Experiments shed new light
� 1928: Fredrick Griffith
� Studying the effects of Streptococcus pneumoniae
� Two strains:
� Smooth- pathogenic
� Rough - harmless
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Transformation
� Demonstrated that “something” passed from one bacteria to the other, changing the bacteria’s properties
� Transformation: the change in genotype and phenotype due to the incorporation of new DNA
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Follow-up experiments� Oswald Avery, Maclyn McCarty and Colin
MacLeod: 14 years of experiments ending in 1944
� Avery originally wanted to disprove transformation but then wanted to know what caused it
� Purified substances from Griffith’s experiment
� Demonstrated that DNA was capable of transforming bacteria
� Results received with skepticism
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Further evidence
� 1952: Alfred Hershey and Martha Chase
� Used bacteriophagesto determine whether the genetic material is DNA or protein
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Hershey-Chase Experiment
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Results
� DNA is the genetic material
� Was there any additional evidence that DNA could have been the genetic material?
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Yep. More evidence
� Scientists already knew that DNA was a polymer of nucleotides
� Sugar, phosphate, base
� 1947: Edwin Chargaff
� Discovered that the base composition of DNA varies across species
� Ratio of DNA bases
� A = 30.3 %
� T = 30.3%
� C = 19.5%
� G = 19.9%
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Ok, we get it already!
� Once accepted as the hereditary molecule, scientists worked to determine the exact structure of DNA
� Competing groups of scientists
� Linus Pauling
� Maurice Wilkins and Rosalind Franklin
� James Watson and Francis Crick
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�Maurice Wilkins and Rosalind Franklin used
X-ray crystallography to study the structure of
DNA
�1953: Watson and Crick used this
used this information to
deduce the double
helical structure of DNA
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DNA structure- The Double Helix
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DNA STRUCTURE
Unit 5- Concept 2
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The Big Idea…
� Living systems store, retrieve, transmit and respond to information essential to life processes.
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How do living things manage information?
� Storage?
� Retrieval?
� Transmission?
� Response?
�DNA!!!� With some help from RNA
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How does DNA or RNA actually do all of this information carrying/storing stuff?
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How does DNA or RNA do this?
� It carries a code.
� The structure of DNA is made of a series of chemical molecules used in a sequence.
� The specific sequence of the molecules produces a code.
� That’s the A T C G stuff
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Mini review
� DNA Structure
� Nucleotide
� Purines and Pyrimidines
� Base pairing rules
� Antiparallel double helix
� DNA is the heritable material
� RNA Structure
� Uracil
� Single strand
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Nucleotide structure
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Two classifications of monomers
� Pyrimidines: Cytosine, Thymine, Uracil
� Purines: Adenine, Guanine
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Numbering of
strands is based
on position of
deoxyribose
sugars
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� Let’s make a model