DNA ( Deoxyribonucleic acid ) 1 DNA structure DNA replication DNA repair.
AIM What is the structure of DNA?. DNA Deoxyribonucleic Acid The material that contains the...
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Transcript of AIM What is the structure of DNA?. DNA Deoxyribonucleic Acid The material that contains the...
AIM
What is the structure of DNA?
DNA
• Deoxyribonucleic Acid• The material that contains the information
that determines inherited characteristics
Gene
• A segment of DNA that is located on a chromosome and codes for a specific trait
• Instructions for inherited traits• Instructions for proteins
Searching for Genetic Material
• Fredrick Griffith: Discovery of Transformation– 1928– 2 strains of bacteria (S causes pneumonia, R
doesn’t)• Transformation: A change in the genotype
(genes) when cells take up foreign genetic material
• Outcome: Genetic Material can be transferred between cells
Searching for Genetic Material
• Oswald Avery: DNA is responsible for transformation– 1940’s– Wanted to see what caused transformation– 3 choices: DNA, RNA and Proteins– Used enzymes to destroy each part– Only when DNA was missing did transformation
not occur• Outcome: DNA is the transforming agent
Searching for Genetic Material
• Alfred Hershey and Martha Chase: DNA is hereditary material– 1952– Studied bacteriophages (viruses that invade
bacteria)• Outcome: DNA is the hereditary material
The Shape of DNA
• James Watson and Francis Crick (February 28, 1953)
• Double Helix shape-strands of repeating subunits joined at the center
Nucleotides
• Subunit of DNA that consists of 3 parts• Phosphate• Deoxyribose Sugar• Nitrogenous Base• The information in DNA is contain in the order
of the nitrogenous bases• Base-pairing structure allows DNA to be
copied quickly
Nitrogenous Bases
Purines• Two rings of Carbon per
base• Adenine• Guanine
Pyramidines• One ring of Carbon per base• Thymine• Cytosine
Base-Pairing
• A purine is always paired with a pyramidine based on their chemical structure
• They are held together with weak Hydrogen bonds
• A always pairs with T• C always pairs with G
Complementary Strands
• Now that we know the base-pairing rule we can construct complementary strands
• If given one strand (side) of the DNA, we can construct the other strand
• EX: TATGAGACT
• This ensures that each strand has the same information, with one side being the reverse of the other
Discovering the Structure of DNA
• Erwin Chargaff: 1949– In every DNA the number of Adenine was equal to
the number of Thymine and the number of Guanine was equal to the number of Cytosine
Discovering the Structure of DNA
• Rosalind Franklin: 1952– Used X-ray diffraction to take pictures of the two
forms of DNA– These photographs show that DNA as it is in
nature has a tightly coiled helix made of two chains of nucleotides
Discovering the Structure of DNA
• James Watson and Francis Crick: 1953– Built models to figure out the structure of DNA– Double Helix with phosphate and deoxyribose
sugars on the outside and nitrogenous bases on the inside
• Watson, Crick and Wilkens were awarded the Nobel Prize in 1962 for their disocovery
• Franklin who had died of Cancer was not named in the award