Presentation on theme: "DNA: The Stuff of Life. Griffith and Transformation In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria caused."— Presentation transcript:
Griffith and Transformation In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria caused pneumonia. He isolated two different strains of pneumonia bacteria from mice and grew them in his lab.
Griffith and Transformation Performed the first major experiment that led to the discovery of DNA as the genetic material
Griffith and Transformation –Transformation Griffith determined that bacteria could pass genetic information from one to another. Griffith called this process transformation because one strain of bacteria (the harmless strain) had changed permanently into another (the disease- causing strain).
Oswald Avery Oswald Avery repeated Griffith’s work to determine which molecule was most important for transformation. Identified the molecule that transformed the R strain of bacteria into the S strain Concluded that when the S cells were killed, DNA was released R bacteria incorporated this DNA into their cells and changed into S cells.
The Hershey-Chase Experiment –Alfred Hershey and Martha Chase studied viruses—nonliving particles smaller than a cell that can infect living organisms. Bacteriophages A virus that infects bacteria is known as a bacteriophage. Bacteriophages are composed of a DNA or RNA core and a protein coat.
The Hershey-Chase Experiment If Hershey and Chase could determine which part of the virus entered an infected cell, they would learn whether genes were made of protein or DNA. They grew viruses in cultures containing radioactive isotopes of phosphorus-32 ( 32 P) and sulfur-35 ( 35 S). Copyright Pearson Prentice Hall
Hershey and Chase Used radioactive labeling to trace the DNA and protein Concluded that the viral DNA was injected into the cell and provided the genetic information needed to produce new viruses
DNA Structure Nucleotides Consist of a five-carbon sugar, a phosphate group, and a nitrogenous base
Two Kinds of Bases in DNA Pyrimidines are single ring bases.Pyrimidines are single ring bases. –Thymine & Cytosine Purines are double ring bases.Purines are double ring bases. –Adenine & Guanine C C C C N N O N C C C C N N N N N C
Chargaff Chargaff’s rule: C = G and T = A The percentages of guanine [G] and cytosine [C] bases are almost equal in any sample of DNA. The percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA.
X-ray Diffraction Rosalind Franklin’s X-ray diffraction data helped solve the structure of DNA Indicated that DNA was a double helix
Watson and Crick Built a model of the double helix that conformed to the others’ research 1. 1. two outside strands consist of alternating deoxyribose and phosphate 2. 2. cytosine and guanine bases pair to each other by three hydrogen bonds 3. 3. thymine and adenine bases pair to each other by two hydrogen bonds
DNA Structure DNA often is compared to a twisted ladder. Rails of the ladder are represented by the alternating deoxyribose and phosphate. The pairs of bases (cytosine–guanine or thymine–adenine) form the steps.
The Components and Structure of DNA Watson and Crick discovered that hydrogen bonds can form only between certain base pairs—adenine and thymine, and guanine and cytosine. This principle is called base pairing. Copyright Pearson Prentice Hall
DNA and Chromosomes –Chromosome Structure Eukaryotic chromosomes contain DNA and protein. The DNA is tightly coiled around proteins called histones. DNA and histone molecules form nucleosomes. Nucleosomes pack together, forming a thick fiber called chromatin. When chromatin is super-coiled it forms the chromosome.
DNA Replication DNA must be copied The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing: A-T, G-C Each strand of the original DNA serves as a template for the new strand
DNA Replication Semiconservative Model: Watson and Crick showed: 1.Watson and Crick showed: the two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand.. Parental DNA DNA Template New DNA
1. Why is replication necessary? 2. When does replication occur? 3. Describe how replication works. 4.Use the complementary rule to create the complementary strand: A--- ? G--- ? C--- ? T--- ? A--- ? G--- ? A--- ? G--- ? C--- ? A--- ? G--- ? T--- ? Replication Quiz
1. Why is replication necessary? So both new cells will have the correct DNA 2. When does replication occur? During interphase (S phase). 3. Describe how replication works. Enzymes unzip DNA and complementary nucleotides join each original strand. 4. Use the complementary rule to create the complementary strand: A--- T G--- C C--- G T--- A A--- T G--- C A--- T G--- C C--- G A--- T G--- C T--- A Replication Quiz
–Avery and other scientists discovered that DNA is found in a protein coat. DNA stores and transmits genetic information from one generation to the next. transformation does not affect bacteria. proteins transmit genetic information from one generation to the next. Questions
–The Hershey-Chase experiment was based on the fact that DNA has both sulfur and phosphorus in its structure Protein has both sulfur and phosphorus in its structure. both DNA and protein have no phosphorus or sulfur in their structure. DNA has only phosphorus, while protein has only sulfur in its structure. Questions
–DNA is a long molecule made of monomers called nucleotides. purines. pyrimidines. sugars. Questions
–Chargaff's rules state that the number of guanine nucleotides must equal the number of cytosine nucleotides. adenine nucleotides. thymine nucleotides. thymine plus adenine nucleotides. Questions
–In DNA, the following base pairs occur: A with C, and G with T. A with T, and C with G. A with G, and C with T. A with T, and C with T. Questions