DNA & RNA The Molecular Basis of Inheritance

1. DNA & RNAThe Molecular Basis of Inheritance

2. DNA & RNAThe Molecular Basis of Inheritance By the 1940’s, scientists knew that chromosomes carried hereditary material and consisted of DNA and proteins. Most thought proteins were the genetic material because it is a complex macromolecule and little was known about nucleic acids.

3. DNAGriffith and Transformation In 1928, Frederick Griffith was trying to determine how bacteria infected people. He isolated two different strains of pneumonia bacteria 1. smooth strain (S) – polysaccharide coat, on the bacterial cell prevents attach by the immune system 2. rough strain (R) – polysaccharide coat is absent and therefore the immune system can kill the bacteria

4. DNAGriffith and Transformation Griffith performed four sets of experiments – Fig. 12-2 Experiment – injected live S strain into the mice; Results – mice developed pneumonia & died Conclusion – S strain causes disease Experiment – injected live R strain into the mice: Results – mice survived Conclusion – R strain does not cause disease

5. DNAGriffith and Transformation Griffith performed four sets of experiments – Fig. 12-2 Experiment – injected heat killed S strain Results – mice survived Conclusion – polysaccharide coat does not cause pneumonia

6. DNAGriffith and Transformation Griffith performed four sets of experiments – Fig. 12-2 Experiment – Heat killed S strain cells mixed with the live R strain cells and then injected into mice Results – mice died from pneumonia & blood samples from dead mice contained living S strain cells Conclusion – R cells had acquired “some factor” to make polysaccharide coat

7. DNAGriffith and Transformation

8. DNAGriffith and Transformation Transformation – the assimilation of external genetic material by a cell The disease causing ability was inherited by the bacterial offspring, therefore information for disease might be located on a gene.

9. Avery & DNA http://www.dnalc.org/view/16375-Animation-17-A-gene-is-made-of-DNA-.html The above link is an explanation of Griffith’s & Avery’s findings. Great site – please review. Avery discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next.

10. Hershey-Chase ExperimentMore evidence that DNA is the genetic material Bacteriophage – a virus that infects a bacterium; made up of DNA or RNA and a protein coat. – Fig. 12-3, 12-4

11. Hershey-Chase ExperimentMore evidence that DNA is the genetic material DNA – contains no sulfur but does have phosphorus Proteins – contain almost no phosphorus but do have sulfur

12. Hershey-Chase ExperimentMore evidence that DNA is the genetic material Hershey & Chase performed two sets of experiments 1. T2 with radioactive phosphorus infects bacterium – 32P shows up in bacterial DNA 2. T2 with radioactive sulfur infects bacterium – 35S does not show up in bacterial DNA 3. Conclusion – genetic material of T2 was DNA not protein

13. Hershey-Chase ExperimentMore evidence that DNA is the genetic material http://highered.mcgraw-hill.com/olc/dl/120076/bio21.swf (Hershey/Chase experiment animation)

14. Structure of DNA- Fig. 12-5 Nucleotide – functional unit; composed of a phosphate group, sugar (deoxyribose), and a nitrogenous base T- thymine A – Adenine G – Guanine C – cytosine Chargaff’s Rules – Fig. 12-6 [A] = [T] [C] = [G]

15. Structure of DNA- Fig. 12-5 X-ray evidence – x shaped pattern shows DNA strands are twisted and nitrogenous bases are in the center (Rosalind Franklin created this image which was used by Watson & Crick to explain the structure of DNA) She probably would have shared in the Nobel Peace Prize with them for this discovery if she had not died.

16. Structure of DNA- Fig. 12-5

17. Structure of DNA- Fig. 12-5

18. Structure of DNA- Fig. 12-5

19. Prokaryotic Cells lack a membrane bound nucleus; only one circular chromosome holds most of the genetic material. Fig. 12-8 Chromosomes & DNA Replication

20. Eukaryotic cells have a membrane bound nucleus; chromosomes are found in pairs and the number is species specific DNA is a very long molecule and must be a tightly folded Chromatin – DNA & histone proteins make up a unit called a nucleosome Fig. 12-10 Chromosomes & DNA Replication

21. The two DNA strand separate Each strand is a template for assembling a complementary strand. Nucleotides line up singly along the template strand in accordance with the base-pairing rules ( A-T and G-C) DNA polymerase links the nucleotides together at their sugar-phosphate groups. http://www.youtube.com/watch?v=hfZ8o9D1tus DNA Replication – Fig. 12-11

22. DNA Replication – Fig. 12-11

23. RNA and Protein Synthesis DNA  RNA  Protein  Trait Stucture of RNA Single stranded Sugar is ribose instead of deoxyribose Uracil (U) replaces Thymine (T)

24. RNA vs DNA

25. Messenger RNA – mRNA, contains “code” or instructions for making a particular protein Ribosomal RNA – rRNA (part of the ribosome), facilitates the orderly linking of amino acids into polypeptide chains Transfer RNA – tRNA, brings amino acids from the cytoplasm to the ribosome Types of RNA – Fig. 12-12

26. mRNA

27. tRNA

28. rRNA

29. Transcription is the synthesis of RNA using DNA as a template: Fig. 12-14 RNA polymerase binds to DNA strand and separates it RNA polymerase will bind to a promoter, a specific “start’ region of the DNA molecule Nucleotides are assembled into a strand of RNA Transcription stops when RNA polymerase reaches a specific “stop” region of the DNA molecule Transcription

30. Transcription

31. http://www.youtube.com/watch?v=aiPHi1d_t5w&feature=related (basic) http://www.youtube.com/watch?v=P6Nyce-4oG4 (advanced) Transcription

32. Only a small portion of the original RNA sequence leaves the nucleus as mRNA because portions are edited out. Fig. 12-15 • Introns are the noncoding sequences in the DNA that are edited out of the pre mRNA molecule • Exons are the coding sequences of a gene that are transcribed and expressed (translated into a protein) RNA Editing

33. RNA Editing

34. Transcription

35. Fig. 12-16, 12-17 • A codon is a three-nucleotide sequence in mRNA that: • signals the starting place for translation • specifies which amino acid will be added to a growing polypeptide chain • signals termination of translation • Some amino acids are coded for by more than one codon The Genetic Code

36. The Genetic Code

37. Fig. 12-18 • Translation is the synthesis of a • polypeptide chain, which occurs under the idrection of mRNA • Three major steps of translation include: Initiation, Elongation, and Termination • Initiation - must bring together the mRNA, two ribosomal subunits, and a tRNA Translation

38. Fig. 12-18 • Elongation – polypeptide assembly line • 1) Codon on mRNA bonds with anticodon site on tRNA • The amino acid that is brought in by tRNA is added to the growing polypeptide chain • 3) tRNA leaves ribosome • Termination – stop codon is reached and the entire complex separates Translation (cont.)

39. Translation

40. Translation (cont.) http://www.youtube.com/watch?v=5bLEDd-PSTQ (translation)

41. From Polypeptide to Functional Protein – depends upon a precise folding of the amino acid chain into a three-dimentional conformation Translation (cont.)

42. Any change in the genetic material is a mutation. Gene mutations – changes in a single gene – Fig. 12-20 1. point mutations – changes involving only one or a few nucleotides (substitution, insertion, deletion) that affects only one amino acid Mutations

43. 2. frameshift mutation (a type of point mutation) – “reading frame” of the genetic message is changed because of insertion or deletion of a nucleotide, therefore the entire sequence of amino acids can change Mutations (cont.)

44. Substitution Mutations (cont.)

45. Insertion and Deletion Mutations (cont.)

46. Chromosomal mutations – changes in the number of structure of chromosomes; includes – deletion, duplication, inversion, and translocation – Fig. 12-21 Mutations (cont.)

47. Genes can be switched “on” or “off” depending on the cell’s metabolic needs, (i.e. muscle cell vs. neuron, embryonic cell vs. adult cell) Fig. 12-22 Gene Regulation

48. Gene Regulation inProkaryotes – Fig. 12-23 Structural gene – gene that codes for a protein Operon – a group of genes that operate together Operator – a DNA segment between an operon’s promoter and structural genes, which controls access of RNA polymerase to structural genes

49. Gene Regulation inProkaryotes – (cont.) Repressor – a specific protein that binds to an operator and blocks transcription of the operon The lacoperon is turned off by repressors and turned on by the presence of lactose.

50. http://www.sumanasinc.com/webcontent/animations/content/lacoperon.html (lacoperon animation) Gene Regulation