Viruses (Ch. 18)

1. Viruses (Ch. 18)

2. 1) A model system: • Organisms frequently used by researchers in order to explore broad biological principles. • Ex: Escherichia Coli- models gram negative prokaryotes • Ex: T4- virus (bacteriophage) • Ex: Drosophila melanogaster (fruit fly) • Ex: yeast (eukaryotic cells)

3. 2) Viral genomes • Double stranded DNA, single-stranded DNA, double-stranded RNA, or single stranded RNA • Depends on the type of virus • Genome organized as either linear or circular • Four genes to 100’s of genes

4. 3) CAPSID = protein shell that surrounds the viral genome • helical • polyhedral • Combination (polyhedral “head” & spiral “tail”)

5. Capsomere of capsid Membranous envelope RNA Capsomere Capsid DNA Head RNA DNA Tail sheath Tail fiber LE 18-4 Glycoprotein Glycoprotein 70–90 nm (diameter) 80–200 nm (diameter) 18  250 mm 80  225 nm 20 nm 50 nm 50 nm 50 nm Tobacco mosaic virus Adenoviruses Influenza viruses Bacteriophage T4

6. GENETIC MATERIAL! PROTEIN! 4) A T-4 Bacteriophage

9. 5) Is a virus alive? No. Not made up of cells; they can only reproduce within a host cell; no enzymes for metabolism; no ribosomes.

10. DNA polymerases Nucleotides Enzymes tRNAs Amino acids ATP 6) Viruses use the host cell’s:

11. 7) HOST RANGE SPECIFICITY • specific receptor molecules on the surface of host cells match proteins on the outside of the virus

12. 8) Lytic Cycle: last stage of infection during which cell lyses (breaks open)20-30 minutes • Virus attaches to host cell at specific receptor sites; • Genetic material of virus is injected into host cell; • Host cell’s DNA is hydrolyzed (if host cell is a bacteria infected by T4); • Host cell produces viral components; phage parts are assembled; • Phage directs production of lysozyme; cell bursts and releases new viral particles.

14. 9) Lysogenic cycle: viral genome is replicated without destroying the host. • Virus binds to host cell & injects genetic material; • Viral DNA is incorporated into the host cell’s DNA at a specific site (viral DNA called a PROPHAGE; most prophage genes are repressed); • As host cell prepares to divide, viral DNA is copied along with host cell DNA *allows replication w/o killing host cell *(trigger to switch to lytic cycle could be radiation, presence of certain chemicals, etc.)

16. 9) Lysogenic cycle: part “c” • A few prophage genes are expressed during lysogenic cycles & these proteins cause the host bacteria to make a toxin and the toxin is harmful to humans

17. 10) Virus “Families”: • Double-stranded DNA • papilloma (warts) • respiratory diseases • herpes • smallpox • Single-stranded DNA • Parvovirus • Double-stranded RNA • Rotavirus • Colorado tick fever virus • Single-stranded RNA (serves as mRNA) • Rhinovirus- common cold • SARS • West Nile virus • Hepatitus C virus

18. 10) Virus “Families”: • Single-stranded RNA (template for mRNA synthesis) • Ebola virus • Influenza virus (flu) • Measles • Mumps • Rabies • Single-stranded RNA (template for DNA synthesis) • HIV • Leukemia (RNA tumor viruses)

19. 11) Herpes virus resides: • Copies of the herpes virus remains behind as “mini-chromosomes” in the nuclei of certain nerve cells • Remain latent until physical or emotional stress triggers new round of active virus production

21. 12) Retrovirus • Virus with RNA as its genetic material • Uses the enzyme “reverse transcriptase” to transcribe its RNA template into DNA • This newly synthesized viral DNA can then integrate in to the host’s DNA

23. 13) What is a vaccine? • Harmless variants or derivatives of pathogenic microbes that stimulate a person’s immune system to mount a defense against the “pathogen” • As part of this defense, your body produces a lot of “memory” cells that will be ready and available if you ever are exposed to the entire pathogen

24. 13) Developed vaccines? • Smallpox • Polio • Measles • Mumps • Rubella • Hepatitis B • Certain strains of influenza • Chicken pox • HPV (human papaloma virus)

25. 13) Antiviral drugs (ex: AZT) • Interfere with viral nucleic acid synthesis • Inhibits viral polymerase used to synthesize viral DNA (Acyclovir/Valtrex) • Interferes with reverse transcriptase & therefore DNA synthesis (AZT)

26. 14) What is an emerging virus? • Viruses that appear suddenly or that suddenly come to the attention of medical scientists • Ex: HIV, Ebola, West Nile virus, SARS

27. 15) What is a prion? • An infectious protein; appear to cause a number of degenerative brain diseases • Ex: scrapie (sheep), mad cow disease, Creutzfeldt-Jakob disease • Most likely transmitted in food • Alarming! • 1) very slow acting agents (incubation until symptoms = 10 years!) • 2) virtually indestructible (NOT deactivated by heat)

28. BACTERIA! (Ch. 18)

29. 1) Bacterial chromosome vs. eukaryotic chromosome • Bacterial chromosome is double-stranded DNA CIRCULAR molecule (little bit of protein) • Bacteria also have plasmids • Eukaryotic chromosome is linear and is associated with a lot of protein

31. 2) What is a plasmid? • Small, circular, self-replicating DNA molecule; contains only a few genes • Separate from the bacterial chromosome • Some can undergo reversible integration into the chromosome

32. 3) Bacterial division • Bacteria divide by binary fission (must be preceded by replication of the bacterial chromosome) • Asexual process (bacterial in a colony are clones) Why not Mitosis? Mitosis = division of NUCLEUS!

33. 4) 3 methods by which prokaryotes achieve genetic recombination • Transformation: alteration of bacterial cell’s genotype by the uptake of naked, foreign DNA from the surrounding environment • Ex: dead, broken-up cells supply the DNA • Transduction: phages (viruses) carry bacterial genes from 1 host cell to another • Conjugation& plasmids: direct transfer of genetic material between 2 temporarily joined bacterial cells • transfer is 1 way • Plasmids can cross over animation

35. 5) Function of Regulatory Gene • They are expressed continuously at a low rate and they control when other genes are expressed • PRODUCT: a protein (of course!)

37. Ch. 27 BACTERIA

38. The purpose of the CELL WALL in bacteria is to maintain cell shape, provide protection, and prevent the cell from bursting in a hypotonic environment. • The cell wall of bacteria contains peptidoglycan (polymers of sugar linked with polypeptides) instead of the cellulose of plant cell walls.

39. 2) The Gram stain is a diagnostic tool to stain bacterial cell walls. Gram + bacteria have simpler cell walls with a large amount of peptidoglycan. Gram – bacteria have less peptidoglycan and are more complex structurally. G. - G. +

40. G. - G. + Gram neg. are generally more threatening than Gram pos.

41. G. - G. +

42. 3) Why does penicillin work? • It competitively inhibits the enzyme that forms peptidoglycan cross-linking. This prevents cell wall formation (especially in gram + bacteria since it’s easier to cross membrane).

43. 4) Some species (like TB-causing bacteria) disrupt health by invading tissues & causing infection. Most species of bacteria cause “sick” symptoms by producing poisons (TOXINS).

44. EXOTOXINS = proteins secreted by prokaryote  More toxic (released by Gram - & Gram +) Clostridium botulinum (disease = botulism) Vibrio cholerae (disease = cholera) ENDOTOXINS = lipopolysaccharide components of the outer membranes of Gram – bacteria; released when bacteria die & cell walls break down or during cell growth Salmonella typhimurium (illness = food poisoning) Salmonella typhi (disease = typhoid fever) E. coli (illness = food poisoning) 5) Exotoxins vs. endotoxins

45. EXO ENDO

46. 6) Practical Applications/Uses of Bacteria: • Models for researching metabolism, molecular biology; • Bioremediation: Decompose of sewage, pesticides, petroleum products, radioactive waste; • Mining industry uses bacteria to recover metal from ores

47. 6) Practical Applications/Uses of Bacteria (continued): • Pharmaceutical production of vitamins, antibiotics, & hormones; • Production of yogurt & cheese;

48. 7 for AP) Operon (gene regulation from Ch 18) • Operon: entire stretch of E. ColiDNA required for the production of enzymes that will ultimately break down the sugar lactose • Includes a promoter region, operator region, and the 3 genes which provide the code to produce the 3 enzymes for lactose metabolism

49. Lac (Lactose) Operon • Within 15 minutes of consuming milk, the E.Coli in your intestines have produced the enzymes necessary to break lactose down. • Operator= switch to turn on/off gene expression • If operator region is blocked, RNA polymerase cannot attach to the promoter region in order for transcription to begin • A regulatory gene produces a protein that sits on the operator, thereby blocking RNA polymerase