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 that genetic information could be passed between organisms.
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). Transformation = the exchange of information between genetic material.
Oswald Avery 1931 - 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).
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
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.
Two Groups 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
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. Model was a double helix 2. 2. Backbone made of sugars and phosphates 3. 3. Base pairs attached to deoxyribose with A & T in equal amounts and C & G in equal amounts.
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 Replication –Duplicating DNA Before a cell divides, it duplicates its DNA in a process called replication. Replication ensures that each resulting cell will have a complete set of DNA. Occurs in the S phase of Interphase.
DNA Replication DNA must be copied in order for cells to multiply in number and maintain genetic information. 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
DNA Replication The sites where separation and replication occur are called replication forks. Nitrogen Bases Replication Fork DNA Polymerase Replication Fork Original strand New Strand
DNA Replication DNA must first unwind and “unzip” DNA helicase, an enzyme, is responsible for unwinding and unzipping the double helix. –Single stranded binding proteins hold the DNA open
DNA Replication DNA polymerase continues adding appropriate nucleotides to the chain by adding to the open end of the new DNA strand.
DNA Replication Okazaki fragments, sections of nucleotides created by replication in small segments, must be joined together. Finally, DNA ligase links the fragments together to form the full complementary strand.
DNA Replication Give the complementary sequence for the following strand of DNA: –DNA 5’ A T C C G A A G C T T 3’ –DNA 3’ T A G G C T T C G A A 5’