DNA, RNA, & Protein Synthesis

1. DNA, RNA, & Protein Synthesis Discovery of DNA DNA Structure DNA Replication Protein Synthesis

2. Introduction • Mendel - concluded that hereditary factors determine many of an organisms traits • But he didn’t know what these hereditary factors were • How did they share info • Answers to these questions emerged during the pneumonia epidemic in London in the 1920s

3. Griffith’s Experiments • Griffith was studying bacterium, Streptococcus pneumoniae • Cause lung disease pneumonia • Trying to develop a vaccine against a disease-causing agent, or virulent strain of the bacterium • S strain & R strain

4. Nature of Hereditary Material • Experiments 1 & 2 • Injected either live R o live S cells into mice • Only S cells killed the mice • Experiment 3 • Injected heat killed S bacteria into mice • Mice survived • Experiment 4 • Injected mice w/ both heat-killed S cells and live R cells • Mice died

5. Conclusions from Griffiths Experemint • ? • Heat-killed virulent bacterial cells release a hereditary factor that transfers the disease-causing ability to the live harmless cells • Transfer of genetic material from one cell to another cell or from one organism to another organism = Transformation • file:///Users/eastlmat/Documents/Biology%20'08-'09/Biology%20PPT/Ch10/60427.html

6. Avery’s Experiments • 1940s, Oswald Avery, wanted to test whether the transforming agent in Griffith’s test was protein, RNA, or DNA • Used enzymes to separately destroy each of the 3 molecules in heat killed S cells • Protease Enzyme • Rnase • DNase

7. What Happened in Avery’s Exp? • They mixed the 3 experimental batches of heat-killed S cells w/ live R cells • What Happened? • Cells missing RNA & Protein were able to transform R cells into S cells = mice died • Cells missing DNA did not transform R cells into S cells = mice survived • DNA is transforming agent

8. Hershey-Chase Experiment • 1952, Martha Chase & Alfred Hershey, tested whether DNA or protein was the hereditary material viruses transfer when viruses enter a bacterium • Viruses that infect a bacterium = bacteriophages

9. Steps of the Experiment • 1: radioactive isotopes to label protein & DNA in the phage • DNA labeled & protein labeled phages were separately allowed to infect E. coli • 2: removed the phage coats • 3: centrifuged to separate the phage from E. coli • Found all viral DNA & little protein entered cells • DNA is the hereditary molecule in viruses • file:///Users/eastlmat/Documents/Biology%20'08-'09/Biology%20PPT/Ch10/61132.html

10. DNA Structure Section 2

11. DNA Double Helix • Watson & Crick in 1953 created a model for the structure of DNA • 2 chains that wrapped around each other • Double helix shape: winding spiral staircase • Used X-ray diffraction and work of many scientists to determine structure

12. DNA Nucleotides • DNA made of: • 2 long chains of nucleotides, which are repeating subunits • Nucleotide consists of: • 5-carbon sugar = deoxyribose • Phosphate group = P atom + 4 Oxygen • Nitrogenous base = N atoms & C atoms, base

13. DNA Nucleotides

14. Bonds Hold DNA Together • DNA Double Helix = Spiral Staircase • Alternating sugar & phosphate molecules = the side “handrails” • Nucleotides connected by covalent bonds • Nitrogenous bases face center & connect w/ bases of opposite strand using H bonds • Either 2 H bonds or 3 H bonds • Form the “steps” of staircase

15. Visual Aid of DNA Bonds

16. Nitrogenous Bases 4 Kinds: Pyrimidines Adenine = A Guanine = G Purines Cytosine = C Thymine = T

17. Complementary Bases • % of Adenine = % of Thymine • % of Cytosine = % of Guanine • Helps understand structure • Base-pairing rules in DNA • Cytosine–––Guanine • Adenine–––Thymine • Complimentary Pairs • C–G • A–T • Notice anything about the pairs?

18. Complimentary Bases • Base Sequence: • AAAATTTGGC on one strand, what is the opposite strand? • TTTTAAACCG • Important for 2 reasons: • H bonds hold together • Explains replication of DNA

19. DNA Replication Section 3

20. How DNA Replication Occurs • DNAReplication = process by which DNA is copied in a cell before mitosis, meiosis, or binary fission • 2 Nucleotide strands separate along the bases • Complimentary strands serve as templates for new strands

21. Steps of DNA Replication • 1: helicase enzyme separate DNA strands by breaking the H bonds • Y-shaped region that results from the separation is a replicationfork

22. Steps of DNA Replication • 2: DNA polymerases add complimentary nucleotides to each strand • Covalent bonds form b/w adjacent nucleotides, deoxyribose sugar and P groups

23. Steps of DNA Replication • 3: DNA polymerases finish & fall off • Results in 2 new DNA strands that are identical • Semi-conservativereplication: replication in which each new DNA molecule has kept one of the 2 original strands

24. Steps of DNA Replication

25. Action at the Replication Fork • DNA synthesis: • Occurs in different directions on each strands • Synthesis of one strand follows the movement of the replication fork • Replication occurs from 5’ to 3’ • http://www.youtube.com/watch?v=nIwu5MevZyg&feature=related

26. Prokaryotic & Eukaryotic Replication • Prokaryotic • 1 circular chromos. • Repl. begins at one place • 2 repl. forks moving in opposite directions at the origin • Repl. continues until entire molecule is copied • Eukaryotic • Long chromos. • DNA polymerase adds nucleotides at 50/sec, if there were only one DNA polym. it would take 53 days to finish • Multiple points of origin for replication • 2 repl forks moving in opposite directions at each origin • Fruit fly has 3500 origin sites

27. DNA Errors in Replication • Usually has great accuracy • 1:1,000,000,000 error chances in paired nucleotides added • Proofreading functions in DNA polymerases • When a mistake does happen a mutation occurs • Mutation = a change in the nucleotide sequence of a DNA molecule • Can have serious effects on fxns of genes • Chemicals & UV light damage DNA & lead to Cancer

28. DNA Replication & Cancer • DNA replication is an amazing process that passes genetic info from cell to cell • It also explains how mutations arise & lead to altered cells • May allow for better survival and repro, & these variations increase in populations over time • May cause diseases, like cancer

29. Protein Synthesis Section 4

30. Flow of Genetic Information • Gene: Hair Color • Directs making of protein, called Melanin, in the hair follicle, through an intermediate • Ribonucleic acid: RNA

31. Flow of Genetic Information • Transcription: • In Nucleus, DNA is template for RNA • Translation: • In Cytoplasm, RNA directs assembly of proteins • Protein Synthesis: • Forming proteins based on information in DNA & carried out by RNA

32. RNA Structure & Function • Contains sugar ribose • Contains nitrogenous base, uracil, instead of thymine • Usually, single stranded • Usually, much shorter than DNA

33. Types of RNA • messenger RNA: mRNA • Single-stranded • Carries instructions from gene to make protein

34. Types of RNA • ribosomal RNA: rRNA • Part of a ribosome • Where protein synthesis occurs

35. Types of RNA • transfer RNA: tRNA • Transfers amino acids to the ribosome to make the protein

37. Transcription • Genetic instructions in a specific gene are transcribed or “rewritten” into an RNA molecule • Takes place in Nucleus in eukaryotes • Cytoplasm in prokaryotes

38. Steps of Transcription • 1: RNA polymerase binds to a promoter • RNA polymerase = enzyme that catalyzes the formation of RNA on DNA template • Promoter = specific nucleotide sequence of DNA where RNA polymerase binds and initiates transcriptions

39. Steps of Transcription • 2: RNA polymerase adds free RNA nucleotides that are complementary to the nucleotides on one of the DNA strands • Results in an RNA molecule • DNA strand = ATCGAC • RNA strand = UAGCUG • Only uses a gene, not the whole DNA strand

40. Steps of Transcription • 3: RNA polymerase reaches a termination signal, or stop signal • Termination signal = specific sequence of nucleotides that marks the end of a gene • Newly formed RNA can now perform its job in the cell

41. The Genetic Code • Def: rules that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid • 3 adjacent nucleotides in mRNA specify an amino acid in a polypeptide • Codon: 3-nucleotide sequence in mRNA that encodes an amino acid, or signifies a start or stop signal

42. Translation • Protein Structure • Made of one or more polypeptides, chains of amino acids linked by peptide bonds • 20 different amino acids in living things • Each polypeptide chain may consist of hundreds or thousands of the 20 a.a., arranged in a specific sequence • Sequence determines how the polypeptides will twist and fold into the 3-D structure of the protein. • Shape is critical to its function

43. Steps of Translation • Step 1: Initiation • 2 Ribosomal subunits, mRNA, and the tRNA carrying methionine bind together • One end of tRNA contains a specific a.a. • Other end contains anticodon = 3 nucleotides on the RNA that are complementary to the sequence of a codon in mRNA

44. Steps of Translation • Step 2: Elongation • tRNA carrying the appropriate a.a., pairs its anticodon with the second codon in the mRNA • Ribosome detaches methionine from the first tRNA • Peptide bond forms b/w methionine & 2nd a.a. • Ribosome moves a distance of 1 codon along mRNA

45. Steps of Translation • Step 3: Elongation, cont’d • 1st tRNA detaches and leaves it’s a.a. behind • Polypeptide chain continues to grow one a.a. at a time

46. Steps of Translation • Step 4: Termination • Ribosome reaches the stop codon, tRNA has no complementary anticodon • Newly made polypeptide falls off

47. Steps of Translation • Step 5: Disassembly • Ribosome complex falls apart • Newly made polypeptide is released • http://www.youtube.com/watch?v=WsofH466lqk&feature=related • http://www.youtube.com/watch?v=5bLEDd-PSTQ

48. The Human Genome • Def: entire gene sequence of the complete genetic content of humans • Now known: 3.2 billion base pairs/10 yrs. • Learn what info the DNA sequences encode • Info is important b/c help diagnose, treat, and prevent genetic disorders, cancer, and infectious diseases