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DNA R37

DNA R37. Who really discovered DNA?. Who played a major role?. Linus Pauling Developed the triple strand structure Rosalind Franklin & Maurice Wilkins X-ray diffraction, crystalline structure, and equidistance between bases Erwin Chargaff Chargaff’s Ratio. DNA and RNA.

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DNA R37

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  1. DNA R37

  2. Who really discovered DNA?

  3. Who played a major role? • Linus Pauling • Developed the triple strand structure • Rosalind Franklin & Maurice Wilkins • X-ray diffraction, crystalline structure, and equidistance between bases • Erwin Chargaff • Chargaff’s Ratio

  4. DNA and RNA I. DNA- deoxyribonucleic acid • A. History of DNA as Genetic Material “code of life” • 1. Griffith and Transformation • a. Frederick Griffith made discovery while investigating bacteria known to produce pneumonia • b. Griffith isolated two different strains of bacteria

  5. 1). Disease causing strain- had smooth edges. When injected into mice caused pneumonia. • 2). Harmless strain- grew with rough edges.

  6. c. When disease causing bacteria heated- mice survived when injected • d. Mixed the heated-killed bacteria and harmless ones. When injected caused pneumonia. Concluded that one strain had been changed into another. Called transformation.

  7. 2. (Oswald) Avery and DNA- group of scientists repeated Griffith’s experiment to discover “transforming” factor. • a. Made extract from heat-killed bacteria • b. Treated extract with enzymes that destroyed proteins, lipids, carbohydrates, and other molecules- transformation still occurred. • c. Repeated using enzymes that would break down DNA. Transformation did not occur! • d. Concluded- DNA carries genetic code

  8. 3. Hershey-Chase Experiment- (1952) showed conclusively that DNA was molecule that carried genetic code • a. Studied viruses known as bacteriophages

  9. b. Used different radioactive markers to label DNA and proteins of bacteriophages

  10. B. The Structure of DNA • 1. DNA made of units callednucleotides • a. Nucleotides made up of 3 parts • 1). 5-carbon sugar called deoxyribose • 2). Phosphate group • 3). Nitrogenous (nitrogen containing)base

  11. a). Four kinds of nitrogenous bases • b). Purines- include adenine and guanine • c). pyrimidines- include cytosine and thymine

  12. b. Backbone of DNA chain formed by sugar and phosphate groups of nucleotides sugar phosphate

  13. 2. Discoveries- understanding DNA’s structure • a. Chargaff’s Rule- ratio of guanine:cytosine and adenine:thymine are equal A = T and G = C

  14. b. X-Ray evidence- 1950’s Rosalind Franklin and Maurice Wilkins used X-ray diffraction to study structure of DNA molecule. Concluded structure was coiled like a spring (helix)

  15. c. The Double Helix- after looking at Franklin and Wilkin’s work, Watson and Crick constructed a model of DNA molecule (1953)

  16. 1). Hydrogen bondsbetween base pairs holds two strands together • 2). Base Pairing–explained Chargaff’s Rule A=T and C=G

  17. In 1962, Watson, Crick and Wilkins received the Nobel Prize in medicine for their work on DNA • Rosalind Franklin had died in 1958 from cancer (most likely caused by working with X-rays) and was not recognized

  18. Complementary Base Pairs • What would the complementary strand look like for the following: • ATGCGGTCCCGAATA TACGCCAGGGCTTAT • CGAGCTTCTAGATCT GCTCGAAGATCTAGA

  19. DNA Replication R39

  20. II. Chromosomes and DNA Replication • A. DNA and Chromosomes- found in botheukaryotic and prokaryotic cells • 1. Prokaryotic cells- DNA located in cytoplasm in single circular DNA molecule (referred to as cell’s chromosome)

  21. The DNA is a bacterium is about 1000 times as long as the bacterium itself. It must therefore by very tightly folded

  22. 2. Eukaryotic Cells- DNA located in cell’s nucleus in form of a number of chromosomes

  23. B. Chromosome Structure- even the smallest of human chromosomes contains 30 million base pairs • 1. Eukaryotic chromosomes are tightly packed together; formed from the substance called chromatin. DNA coiled around proteins called histones

  24. 2. Nucleosome- DNA wrapped around histones

  25. C. DNA Replication • 1. Duplicating DNA- before cell divides, it duplicates it’s DNA in a process called replication • a. First,DNA molecule’s hydrogen bonds break and the DNA separates into two strands (helicase enzymes) • b. Two new complementary strands are produced (base pairing) each strand serves as template for new strand • c. Process carried out by series of enzymes (DNA polymerase)

  26. 5’ vs. 3’ • 5’ end • Phosphate • 3’ end • OH- • Read from 3’ to 5’ • Synthesized from 5’ to 3’

  27. DNA Interactive • www.dnai.org • “Copying the Code” • “Putting it Together”-Replication • Watch the Videos & do the Activity

  28. DNA PRACTICE WORKSHEET

  29. GENES AND RNA R40

  30. Nucleotides in DNA are grouped into genes, which contain the information required for the production of specific proteins

  31. One gene, one polypeptide • George Beadle & Edward Tatum • Orange bread mold (Neurospora crassa) • “One gene-one enzyme” hypothesis • Genes actually dictate the production of a single polypeptide (part that makes up a protein/enzyme). • One gene-one polypeptide

  32. D. RNA and Protein Synthesis • 1. Structure of RNA- 3 main differences between RNA and DNA • a. Sugar in RNA isribose • b. RNA is single stranded • c. RNA contains uracil in place of thymine

  33. 2. Most RNA involved inProtein Synthesis • 3. 3 Types of RNA • a. Messenger RNA (mRNA)- disposable copy of DNAto carry instructions to rest of cell • b. Ribosomal RNA (rRNA)- helps to assemble proteins on ribosomes. • c. Transfer RNA (tRNA)- transfers amino acids to ribosomes to construct protein molecules

  34. 4. Ribosomes are the factories where proteins are made.

  35. E. Transcription- process by which DNA makes complementary sequence of RNA • 1. Enzyme (RNA Polymerase) separates DNA strand • 2. One strand of DNA is used as template to assemble a strand of RNA. This takes place in nucleus

  36. 3. Transcription begins at specific locations on DNA (promoters)

  37. DNA Interactive • www.dnai.org • “Copying the Code” • “Putting it Together”-Transcription • Watch the Videos & do the Activity

  38. Protein Synthesis R41

  39. F. Translations- “making Proteins” Translating language of nucleic acids (base sequences) into language of proteins (amino acids) • 1. Gene carries code to make one protein (300 to 3000 base pairs) • a. Code written in language with only 4 “letters” • b. Code read 3 letters at a time (each 3 letter “word” known as a codon UCGCACGGU UCG – CAC – GGU Represents the amino acids Serine – Histidine – Glycine

  40. Triplet Code Figure 11-13 Each codon stands for a particular amino acid. The codon AUG not only stands for methionine (Met), but also functions as a signal to "start" translating an RNA transcript. There are also three "stop" codons that do not code for amino acids, but signal the end of each genetic message.

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