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The Structure of DNA

The Structure of DNA. De oxy ribo nucleic acid (DNA) Stores info., copies itself Directs cell activities hereditary material passed from cell → cell Nucleic Acid – polymer; monomer = nucleotide . two kinds: DNA and RNA. Sections in a DNA mol. called genes .

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The Structure of DNA

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  1. The Structure of DNA

  2. Deoxyribonucleic acid (DNA) Stores info., copies itself Directs cell activities hereditary material passed from cell → cell Nucleic Acid – polymer; monomer = nucleotide. two kinds: DNA and RNA.

  3. Sections in a DNA mol. called genes. • Genes code for proteins; • the hereditary info. in DNA tells cell how to make proteins

  4. Nucleotide: three components (CP: 230) (Hon: 197) 5 C sugar phosphate group nitrogenous base(4 kinds in DNA)

  5. Nucleotide: three components (CP: 230) (Hon: 197) a 5-carbon sugar a phosphate group a nitrogenous base(4 kinds in DNA)

  6. O N N O N N N N C C C C N O C C C C C C C C O C N N N N C C N N C C Cytosine C Guanine Thymine Adenine C N N Four Kinds of Nitrogenous Bases • Pyrimidines - single ring bases. • Thymine and Cytosine • Purines - double ring bases. • Adenine and Guanine • Base pairs (also called nucleotide pairs) are formed when a purine bonds with a pyrimidine • A-T and C-G (always)

  7. DNA STRUCTURE Shape is like twisted ladder. Called a double helix -two strands bonded together & twisted The bases form the rungs of the ladder hydrogen bonds hold pairs together; A-T, C-G Sugarsand phosphates form sides of ladder.

  8. The carbons in the sugar are labeled

  9. DNA Animation http://www.johnkyrk.com/DNAanatomy.html http://207.207.4.198/pub/flash/24/menu.swf

  10. Packaging DNA • Eukaryotic DNA: many levels of packaging: • Fundamental unit is Nucleosome – • DNA wound around proteins called histones. • (CP. 139) • (Hon 151)

  11. Nucleosome

  12. Nucleosomes • Nucleosomes • Lowest DNA packaging level • Can be thought of as a length of thread wound around a spool, the thread representing DNA and the spool being histone proteins.

  13. The earth is 150 billion meters or 93 million miles from the sun. DNA - By The Numbers! • Each cell has about 2 meters (6 ft) of DNA. • The average human has 60-75 trillion cells. • Avg human has enough DNA to go from the Earth to the sun more than 400 times. • DNA has a diameter of only 0.0000000002 meters (20Ǻ) [1Ǻ =10-10 m]

  14. Karyotypes • Normal human male karyotype(the total set of chrom. of an organism)

  15. Karyotypes • Normal human female karyotype

  16. The History of DNA • Gregor Mendel-1866 • Determined “Unit characters” were the method of passing on traits for inheritance • Friedrich Meischer - 1868 • Studied nuclei of pus cells obtained from discarded surgical bandages • Detected a phosphorus-containing substance that he named nuclein.

  17. Frederick Griffith 1928 : Work with Bacteria Found that DNA taken from a virulent (disease-causing) strain of bacteria (Streptococcus pneumoniae) Transformed a non-virulent form of the bacterium into a virulent form.

  18. Oswald Avery, Colin MacLeod, and Maclyn McCarty 1943Continued the study of “Transformation” principle

  19. Meischer Mendel Griffith MacLeod McCarty Avery

  20. Transformation Of BacteriaTwo Strains Of Streptococcus Capsule Rough Strain (Harmless) Smooth Strain w/Capsule (Virulent)

  21. Control Control Control Experimental Transformation Of Bacteria -Griffith’s Experiment Smooth (virulent) OUCH! Rough

  22. The History of DNA • Alfred Hershey and Martha Chase - 1952 • radioactive isotope tracer experiment • bacterial virus (bacteriophageT2) infects a host cell ( bacterium Escherichia coli) • found that T2 virus DNA, not its protein coat, enters the host cell • genetic information for replication of the virus

  23. T 2 grown in media containing S35 incorporate S35 into their proteins Bacteria grown in normal non-radioactive media T2 attach to bacteria and inject genetic material Mix-O-Matic Blending causes phage protein coat to fall off Using S35 When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet. The supernatant is radioactive, but the pellet is not. Did protein enter the bacteria? Is protein the genetic material?

  24. T2 grown in P32 containing media incorporate P32 into their DNA Bacteria grown in normal non-radioactive media T2 attach to bacteria and inject genetic material Mix-O-Matic Blending causes phage protein coat to fall off Using P32 When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet The pellet is radioactive, but the supernatant is not. Did DNA enter the bacteria? Is DNA the genetic material?

  25. The History of DNA Structure • Erwin Chargaff- 1940 - “Chargaff’s rule” • four bases may occur in varying proportions in DNA of different organisms • # of A = # of T, w/ two hydrogen bonds • = # of G and C are present w/ 3 hydrogen bonds • Rosalind Franklin and Maurice Wilkins • X-ray diffraction study concluded DNA fibers have two strands.

  26. The History of DNA Structure • James Watson and Francis Crick - University of Cambridge -1953 • Worked on problem of making a DNA molecule model that was double stranded but also had the specific A - T and G - C base equivalencies • Solution-double helical structure for DNA.

  27. Franklin Chargaff Wilkins

  28. Watson and Crick

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