CHAPTER 12 Molecular Genetics

1. CHAPTER 12 Molecular Genetics

2. Today covering pages 329-335

3. Molecular Genetics Chapter 12 DNA Structure • Nucleotides (thymine, cytosine, adenine, guanine, uracil) • Consist of a five-carbon sugar, a phosphate group, and a nitrogenous base

4. Molecular Genetics Chapter 12 Chargaff • Chargaff’s rule: C = G and T = A

5. Molecular Genetics Chapter 12 Watson and Crick • Built a model of the double helix that conformed to 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

6. Molecular Genetics Chapter 12 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.

7. Molecular Genetics Chapter 12 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′. • This is called “antiparallel”

8. Molecular Genetics Chapter 12 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.

9. The gist More accurate How DNA is Replicated

10. 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 Semiconservative Replication

11. Molecular Genetics Chapter 12 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.

12. Molecular Genetics Chapter 12 Base pairing • DNA polymerase III continues adding appropriate nucleotides to the chain by adding to the 3′ end of the new DNA strand.

13. Molecular Genetics Chapter 12 • One strand is called the leading strand and is elongated as the DNA unwinds. • 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.

14. Molecular Genetics Chapter 12 Joining • DNA polymerase I removes the RNA primer and fills in the place with DNA nucleotides. • DNA ligase links the two sections.

15. Molecular Genetics Chapter 12 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.

16. Molecular Genetics Chapter 12 • RNA • Contains the sugar ribose and the base uracil • Usually is single stranded

17. Molecular Genetics Chapter 12 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

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

19. Molecular Genetics Chapter 12 RNA Processing • The code on the DNA is interrupted periodically by sequences that are not in the final mRNA. • Intervening sequences are called introns. Introns may code for gene expression or help to prevent mistakes in the DNA sequence • Remaining pieces of DNA that serve as the coding sequences are called exons. The code provided by exons is translated into amino acids.

20. Molecular Genetics Chapter 12 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.

21. Molecular Genetics Chapter 12 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.

23. Molecular Genetics Chapter 12 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.

24. Molecular Genetics Chapter 12 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

25. Molecular Genetics Chapter 12 Mutations • A permanent change that occurs in a cell’s DNA is called a mutation. • Types of mutations • Point mutation • Insertion • Deletion

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

27. Molecular Genetics Chapter 12 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.

28. Molecular Genetics Chapter 12 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.

29. Read only pages 364-366 and 370-371 THIS INFORMATION WILL BE ON WEDNESDAY’S TEST!!!! Chapter 13

30. DNA and Gene Technology • Bacteria contain enzymes that act as a defense against viruses. • Shaped so that they cut viral DNA at a specific sequence. • Called restriction enzymes • Cutting creates “sticky ends” • EcoRI cuts at GAATTC

31. Useful because we know exactly where they will cut strands of DNA Sticky ends are important because we can insert other pieces of DNA that are complementary Human genome is 2.9 million base pairs (bp) Restriction Enzymes

33. Gel Electrophoresis • Separates DNA fragments by size • Everyone’s DNA is unique, your gel will not look like anyone else’s • DNA fragments are negatively charged so will be attracted to the (+) end of the gel when the current is run through it • SO ALWAYS LOAD A GEL AT THE (-) END!! • Loading a gel

34. Smaller fragments of DNA move faster through the gel Heavier fragments stay closer to the well

35. Some bacterial genes are circular Called plasmids Plasmids used as a vector for a gene of interest Recombinant DNA can then be inserted into bacteria, process is called transformation Recombinant DNA

37. Transgenic organisms have had genes from a different species inserted in them Transgenic plants can be made to be resistant to pests Transgenic bacteria are used for many purposes Medicines- insulin, other hormones Bioremediators Transgenic Organisms

38. Transgenic organisms Golden rice