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Chapter 12 Molecular Genetics

Chapter 12 Molecular Genetics. Section 1: DNA: The Genetic Material. Section 2: Replication of DNA. Section 3: DNA, RNA, and Protein. Section 4: Gene Regulation and Mutation. http://student.ccbcmd.edu/~gkaiser/biotutorials/index.html.

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Chapter 12 Molecular Genetics

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  1. Chapter 12 Molecular Genetics Section 1: DNA: The Genetic Material Section2: Replication of DNA Section 3: DNA, RNA, and Protein Section 4: Gene Regulation and Mutation http://student.ccbcmd.edu/~gkaiser/biotutorials/index.html http://glencoe.mcgraw-hill.com/sites/0078757134/student_view0/ http://library.thinkquest.org/C0118084/Genetic_Engineering.htm

  2. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material Griffith • Performed the first major experiment that led to the discovery of DNA as the genetic material

  3. The First demonstration of bacterial transformation. Experiments done by Frederick Griffith (in London) in 1928 found there were two different types of the bacterium Streptococcus pneumoniae: An "S" or SMOOTH coat strain, which is lethal to mice. An "R" or ROUGH strain, which will not hurt the mouse. Griffith found that he could heat inactivate the smooth strain. DNA is the genetic material

  4. However, if he were to take a mixture of the heat-inactivated S strain, mixed with the R strain, the mouse would die.  Thus there was some material in the heat-killed S strain that was responsible for "transforming" the R strain into a lethal form. Fred Griffith (and a lab co-worker) was killed in their laboratory in 1940 from a German bomb.  Fredrick Griffith

  5. in 1944, Oswald Avery, C.M. MacLeod, and M. McCarty carefully demonstrated that the ONLY material that was responsible for the transformation was DNA Thus, DNA was the "Genetic material" - however, many scientists were still not sure that it was REALLY DNA (and not proteins) that was the genetic material. Griffith’s work continued in U.S.

  6. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material Oswald Avery • 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.

  7. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material Hershey and Chase (1952) • Used radioactive labeling to trace the DNA (P) and protein (S) • Concluded that the viral DNA was injected into the cell and provided the genetic information needed to produce new viruses

  8. Molecular Genetics Chapter 12

  9. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material DNA Structure • Nucleotides • Consist of a five-carbon sugar, a phosphate group, and a nitrogenous base

  10. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material • Chargaff’s rule: C = G and T = A • Pyrimidines = Cytosine and Thymine • Purines = Guanine and Adenine In 1950, Erwin Chargaff analyzed the base composition of DNA composition in a number of organisms. He reported that DNA composition varies from one species to another. Such evidence of molecular diversity, which had been presumed absent from DNA, made DNA a more credible candidate for the genetic material than protein.

  11. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material X-ray Diffraction Structure Analysis (1951-1952) • X-ray diffraction data helped solve the structure of DNA • Indicated that DNA was a double helix This is the famous Rosalind Franklin - Picture 51 which was leaked to James Watson and Francis Crick by Maurice Wilkins. Sodium deoxyribose nucleate from calf thymus, Structure B, Photo 51, taken by Rosalind E. Franklin and R.G. Gosling (her student). Linus Pauling's holographic annotations are to the right of the photo. May 2, 1952

  12. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material X-ray Diffraction Rosalind Franklin (1920 - 1958) The technique with which Maurice Wilkins and Franklin set out to do this is called X-ray crystallography. With this technique a crystal is exposed to x-rays in order to produce a diffraction pattern. • If the crystal is pure enough and the diffraction pattern is acquired very carefully, it is possible to reconstruct the positions of the atoms in the molecules that comprise the basic unit of the crystal. Rosalind Franklin died from cancer in April of 1958, at the age of 37.

  13. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material Watson and Crick 1953 • Built a model of the double helix that conformed to the others’ research two outside strands consist of alternating deoxyribose and phosphate cytosine and guanine bases pair to each other by three hydrogen bonds thymine and adenine bases pair to each other by two hydrogen bonds

  14. The rules of the Nobel Prize forbid posthumous nominations; because Rosalind Franklin had died in 1958 she was not eligible for nomination to the Nobel Prize subsequently awarded to Crick, Watson, and Wilkins in 1962. The award was for their body of work on nucleic acids and not exclusively for the discovery of the structure of DNA. By the time of the award Wilkins had been working on the structure of DNA for over 10 years, and had done much to confirm the Crick-Watson model. Crick had been working on the genetic code at Cambridge and Watson had worked on RNA for some years. Nobel Prize in Medicine/Physiology

  15. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material DNA Structure – Double Helix • 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.

  16. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material Orientation • On the top rail, the strand is said to be oriented 5′ to 3′. • The strand on the bottom runs in the opposite direction and is oriented 3′ to 5′.

  17. Molecular Genetics Chapter 12 12.1 DNA: The Genetic Material Chromosome Structure • DNA coils around histones to form nucleosomes, which coil to form chromatin fibers. • The chromatin fibers supercoil to form chromosomes that are visible in the metaphase stage of mitosis.

  18. Parental strands of DNA separate, serve as templates, and produce DNA molecules that have one strand of parental DNA and Molecular Genetics one strand of new DNA. Chapter 12 12.2 Replication of DNA Semiconservative Replication

  19. Molecular Genetics Chapter 12 12.2 Replication of DNA Unwinding • DNA helicase, an enzyme, is responsible for unwinding and unzipping the double helix. • RNA primase adds a short segment of RNA, called an RNA primer, on each DNA strand. Keeping the DNA strands separate.

  20. Molecular Genetics Chapter 12 12.2 Replication of DNA Base pairing • DNA polymerase (an enzyme) continues adding appropriate nucleotides to the chain by adding to the 3′ end of the new DNA strand.

  21. Molecular Genetics Chapter 12

  22. Molecular Genetics Chapter 12 12.2 Replication of DNA • One strand is called the leading strand and is elongated as the DNA unwinds so is said to be synthesized continuously. • The other strand of DNA, called the lagging strand, elongates away from the replication fork. • The lagging strand is synthesized discontinuously into small segments, called Okazaki fragments.

  23. Molecular Genetics Chapter 12 12.2 Replication of DNA Joining • DNA polymerase removes the RNA primer and fills in the place with DNA nucleotides. • DNA ligase links the two sections.

  24. Molecular Genetics Chapter 12 12.2 Replication of DNA Comparing DNA Replication in Eukaryotes and Prokaryotes • Eukaryotic DNA unwinds in multiple areas as DNA is replicated. • In prokaryotes, the circular DNA strand is opened at one origin of replication.

  25. Molecular Genetics Chapter 12 12.3 DNA, RNA, and Protein Central Dogma: DNA to RNA to Protein • RNA • Contains the sugar ribose (instead of deoxyribose) and the base uracil (instead of thymine) • Usually is single stranded

  26. Molecular Genetics Chapter 12 12.3 DNA, RNA, and Protein Messenger RNA (mRNA) • Long strands of RNA nucleotides that are formed complementary to one strand of DNA Ribosomal RNA (rRNA) • Associates with proteins to form ribosomes in the cytoplasm Transfer RNA (tRNA) • Smaller segments of RNA nucleotides that transport amino acids to the ribosome where proteins are made by adding 1 a.a. at a time

  27. Molecular Genetics Chapter 12 12.3 DNA, RNA, and Protein

  28. Molecular Genetics Chapter 12

  29. Molecular Genetics • DNA is unzipped in the nucleus and RNA polymerasebinds to a specific section where an mRNA will be synthesized. Chapter 12 12.3 DNA, RNA, and Protein Transcription • Through transcription, the DNA code is transferred to mRNA in the nucleus.

  30. Molecular Genetics Chapter 12

  31. Molecular Genetics Chapter 12 12.3 DNA, RNA, and Protein RNA Processing • The code on the DNA is interrupted periodically by sequences that are not in the final mRNA – introns removed.. • Intervening sequences are called introns. • Remaining pieces of DNA that serve as the coding sequences are called exons. DNA and Genes

  32. Molecular Genetics Chapter 12 12.3 DNA, RNA, and Protein The Code • Experiments during the 1960s demonstrated that the DNA code was a three-base code. • The three-base code in DNA or mRNA is called a codon.

  33. Molecular Genetics Chapter 12 12.3 DNA, RNA, and Protein Translation • In translation, tRNA molecules act as the interpreters of the mRNA codon sequence. • At the middle of the folded strand, there is a three-base coding sequence called the anticodon. • Each anticodon is complementary to a codon on the mRNA.

  34. Molecular Genetics Chapter 12 12.3 DNA, RNA, and Protein Visualizing Transcription and Translation

  35. Molecular Genetics Chapter 12 12.3 DNA, RNA, and Protein One Gene—One Enzyme • The Beadle and Tatum experiment showed that one gene codes for one enzyme. We now know that one gene codes for one polypeptide. DNA from the Beginning

  36. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation ProkaryoteGene Regulation • Ability of an organism to control which genes are transcribed in response to the environment • Anoperon is a section of DNA that contains the genes for the proteins needed for a specific metabolic pathway. • Operator • Promoter • Regulatory gene • Genes coding for proteins

  37. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation The Trp Operon

  38. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation The Lac Operon Lac-Trp Operon

  39. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation Eukaryote Gene Regulation • Controlling transcription • Transcription factors ensure that a gene is used at the right time and that proteins are made in the right amounts • The complex structure of eukaryotic DNA also regulates transcription.

  40. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation Hox Genes • Hox genes are responsible for the general body pattern of most animals.

  41. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation RNA Interference • RNA interference can stop the mRNA from translating its message.

  42. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation Mutations • A permanent change that occurs in a cell’s DNA is called a mutation. • Types of mutations • Point mutation • Insertion • Deletion

  43. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation

  44. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation Protein Folding and Stability • Substitutions also can lead to genetic disorders. • Can change both the folding and stability of the protein

  45. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation Causes of Mutation • Can occur spontaneously • Chemicals and radiation also can damage DNA. • High-energy forms of radiation, such as X rays and gamma rays, are highly mutagenic.

  46. Molecular Genetics Chapter 12 12.4 Gene Regulation and Mutation Body-cell v. Sex-cell Mutation • Somatic cell mutations are not passed on to the next generation. • Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.

  47. Molecular Genetics Chapter 12 Chapter Resource Menu Chapter Diagnostic Questions Formative Test Questions Chapter Assessment Questions Standardized Test Practice biologygmh.com Glencoe Biology Transparencies Image Bank Vocabulary Animation Click on a hyperlink to view the corresponding lesson.

  48. Molecular Genetics Chapter 12 Chapter Diagnostic Questions Which scientist(s) definitively proved that DNA transfers genetic material? Watson and Crick Mendel Hershey and Chase Avery

  49. Molecular Genetics Chapter 12 Chapter Diagnostic Questions Name the small segments of the lagging DNA strand. ligase Okazaki fragments polymerase helicase

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