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The Discovery and Structure of DNA

Explore the experiments and discoveries that led to the understanding of DNA, including Griffith's transformation, Avery's identification of DNA as the genetic material, the Hershey-Chase experiment, and the structure of DNA by Franklin, Watson, and Crick.

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The Discovery and Structure of DNA

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  1. Chapter #12 – DNA, RNA, & Protein Synthesis

  2. I. DNA – experiments & discoveries A. Griffith and Transformation Frederick Griffith – British scientist who experimented with bacterial strains of pneumonia in mice & discovered transformation. Transformation – process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria, ex : rough, harmless bacteria becoming smooth & disease-causing.

  3. Griffith & Transformation

  4. B. Avery and DNA Oswald Avery – Canadian biologist who repeated Griffith’s work & found that DNA causes transformation in bacteria. -His work showed that DNA stores & transmits genetic info from one generation of an organism to the next.

  5. C. The Hershey-Chase Experiment Alfred Hershey & Martha Chase – American scientists who experimented with radioactive markers in viruses & concluded that the genetic material of the bacteriophage was DNA, not protein. Virus – nonliving particles smaller than a cell that can infect living organisms. Bacteriophage – (“bacteria eater”) type of virus that infects bacteria. -Scientists conclude that genes are made of DNA.

  6. Alfred Hershey & Martha Chase

  7. D. Components & Structure of DNA DNA – (Deoxyribonucleic acid) nucleic acid that contains the sugar deoxyribose; the molecule of heredity. -DNA (nucleic acid) is made up of nucleotides. Nucleotides of DNA have 3 basic parts : 1. A 5-carbon sugar called deoxyribose. 2. A phosphate group. 3. A nitrogenous (nitrogen-containing) base. -There are 4 kinds of nitrogenousbases found in DNA : 1. Adenine (A) 2. Guanine (G) 3. Cytosine (C) 4. Thymine (T)

  8. Structure of DNA

  9. The 4 bases can be divided into 2 major groups : Purines – have 2 rings in their structures & include adenine & guanine. Pyrimidines – have 1 ring in their structure & include cytosine & thymine. -The backbone of the DNA molecule is formed by sugar & phosphate groups of each nucleotide & the nitrogenous bases stick out sideways from the chain. -Nucleotides can be joined together in any order to make different sequences of bases. Chargaff’s Rule : In any sample of DNA, the percentages of guanine & cytosine bases are nearly equal & the percentages of adenine & thymine bases are nearly equal.

  10. Rosalind Franklin Rosalind Franklin – British scientist who used a technique called X-ray diffraction to Record information about the structure of DNA. -Her work revealed that DNA is shaped like a helix (twisted strands like the coils of a spring).

  11. James Watson and Francis Crick James Watson & Francis Crick – American biologist & British physicist who built the first accurate structural model of DNA, after viewing Rosalind Franklin’s work. -Watson & Crick’s model of DNA was a double helix, in which 2 strands were wound around each other.

  12. The Twisted Ladder -A double helix looks like a twisted ladder or a spiral staircase. -In DNA, hydrogen bonds only form between certain nitrogenous bases in the double helix to hold it together, this is known as base pairing. -Every adenine molecule binds with a thymine and every cytosine molecule binds with a guanine.

  13. Applying Concepts : *Given this sequence, determine the bases that would match it in a double helix : A C G T C T G C A G

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