Bacteria and Viruses

1. Bacteria and Viruses Soja AP - biology

2. Domain Bacteria Domain Archaea Domain Eukarya Common ancestor Prokaryotes Domain Bacteria Domain Archaebacteria

3. Bacteria live EVERYWHERE! • Bacteria live in all ecosystems • on plants & animals • in plants & animals • in the soil • in depths of the oceans • in extreme cold • in extreme hot • in extreme salt • on the living • on the dead Microbes alwaysfind a way tomake a living!

4. Bacterial diversity rods and spheres and spirals… Oh My!

5. eukaryote cell prokaryotecell Prokaryote Structure • Unicellular • bacilli, cocci, spirilli • Size • 1/10 size of eukaryote cell • 1 micron (1um) • Internal structure • _________________________________ • _____________________________ • _____________________________ • _________________________________ • not wrapped around proteins

6. outer membrane of lipopolysaccharides Gram-negative bacteria Gram-positive bacteria peptide side chains outer membrane cell wall peptidoglycan cell wall peptidoglycan plasma membrane plasma membrane protein Prokaryote Cell Wall Structure That’simportant foryour doctorto know! peptidoglycan = polysaccharides + amino acid chains lipopolysaccharides = lipids + polysaccharides

7. Genetic variation in bacteria • Mutations • bacteria can reproduce every 20 minutes • ______________________ • error rate in copying DNA • 1 in every 200 bacteria has a mutation • you have billions of E. coli in your gut! • lots of mutation potential! • Genetic recombination • bacteria swap genes • ____________________ • small supplemental circles of DNA • ____________________ • direct transfer of DNA conjugation

8. Bacteria as beneficial (& necessary) • Life on Earth is dependent on bacteria • ___________________________ • recycling of nutrients from dead to living • ___________________________ • only organisms that can fix N from atmosphere • needed for synthesis of proteins & nucleic acids • plant root nodules • ___________________________ • digest cellulose for herbivores • cellulase enzyme • produce vitamins K & B12 for humans • _________________________ • from yogurt to insulin

9. Structure of Viruses Viruses • Are very small infectious particles consisting of nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope • Not Considered to be living organisms

10. Viral Genomes • Viral genomes may consist of • Double- or single-stranded DNA • Double- or single-stranded RNA

11. Capsomereof capsid RNA DNA Capsomere Glycoprotein 18  250 mm 70–90 nm (diameter) 20 nm 50 nm (b) Adenoviruses Figure 18.4a, b (a) Tobacco mosaic virus Capsids and Envelopes • A capsid • Is the protein shell that encloses the viral genome • Can have various structures

12. Membranousenvelope Capsid RNA Glycoprotein 80–200 nm (diameter) 50 nm (c) Influenza viruses Figure 18.4c Viral Envelopes Some viruses have envelopes • Which are membranous coverings derived from the membrane of the host cell

13. Head DNA Tail sheath Tail fiber 80  225 nm 50 nm (d) Bacteriophage T4 Figure 18.4d Bacteriophages Bacteriophages, also called phages • Have the most complex capsids found among viruses

14. General Features of Viral Reproductive Cycles • Viruses are obligate intracellular parasites • They can reproduce only within a host cell • Each virus has a host range • A limited number of host cells that it can infect

15. VIRUS DNA Entry into cell and uncoating of DNA Capsid Transcription Replication HOST CELL Viral DNA mRNA Viral DNA Capsid proteins Self-assembly of new virus particles and their exit from cell Figure 18.5 Viral Reproduction • Viruses use enzymes, ribosomes, and small molecules of host cells • To synthesize progeny viruses

16. The Lytic Cycle • The lytic cycle • Is a phage reproductive cycle that culminates in the death of the host • Produces new phages and digests the host’s cell wall, releasing the progeny viruses

17. The Lysogenic Cycle • The lysogenic cycle • Replicates the phage genome without destroying the host • Temperate phages • Are capable of using both the lytic and lysogenic cycles of reproduction

18. Glycoprotein Viral envelope Capsid RNA(two identicalstrands) Reversetranscriptase Figure 18.9 Retroviruses Retroviruses, such as HIV, use the enzyme reverse transcriptase • To copy their RNA genome into DNA, which can then be integrated into the host genome as a provirus

19. 1 Reverse transcriptase catalyzes the synthesis of a DNA strand complementary to the viral RNA. 2 The virus fuses with the cell’s plasma membrane. The capsid proteins are removed, releasing the viral proteins and RNA. Membrane of white blood cell HIV Reverse transcriptase catalyzes the synthesis ofa second DNA strand complementary to the first. 3 Reverse transcriptase HOST CELL Viral RNA 4 The double-stranded DNA is incorporated as a provirus into the cell’s DNA. RNA-DNAhybrid 0.25 µm HIV entering a cell DNA ChromosomalDNA NUCLEUS Provirus 5 Proviral genes are transcribed into RNA molecules, which serve as genomes for the next viral generation and as mRNAs for translation into viral proteins. RNA genomefor the nextviral generation mRNA 6 The viral proteins include capsid proteins and reverse transcriptase (made in the cytosol) and envelope glycoproteins (made in the ER). 7 Capsids are assembled around viral genomes and reverse transcriptase molecules. Vesicles transport the glycoproteins from the ER to the cell’s plasma membrane. 8 9 New viruses bud off from the host cell. Figure 18.10 New HIV leaving a cell • The reproductive cycle of HIV, a retrovirus

20. Vaccines • Vaccines • Are harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the actual pathogen • Can prevent certain viral illnesses

21. Figure 18.12 Viral Diseases in Plants • More than 2,000 types of viral diseases of plants are known • Common symptoms of viral infection include • Spots on leaves and fruits, stunted growth, and damaged flowers or roots