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Viruses and Bacteria. Viral structure –DNA or RNA genome –Capsid Protein coat.

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Presentation on theme: "Viruses and Bacteria. Viral structure –DNA or RNA genome –Capsid Protein coat."— Presentation transcript:

1 Viruses and Bacteria

2 Viral structure –DNA or RNA genome –Capsid Protein coat

3 Tobacco mosaic virus

4 Adenovirus

5 T4 bacteriophage

6 Viruses are not cells Cannot metabolize independently Forces infected host cells to replicate viral DNA Takes over cell’s translation and transcription to reproduce

7 Origin of viruses –Escaped gene hypothesis Viruses are often host species- specific Similarity of virus genome to host genome

8 Origin prior to divergence of the three domains –Similarities between protein structures of capsids –Genetic similarities between viruses that infect the Eubacteria and the Archaea –Convergent evolution unlikely

9 Phages infecting E. coli bacterium

10 Lytic cycle –Destroys the host cell Attachment Penetration Replication Assembly Release

11 Lytic cycle

12 Lysogenic cycle –Usually does not kill the host –Viral genome replicated along with host DNA Attachment Penetration Integration Replication

13 Lysogenic cycle

14 Viral infection of animal cells –Surface attachment proteins bind to specific cell receptors –Fuse with plasma membrane –Endocytosis

15 Membrane Fusion

16 Endocytosis

17 Viral infection of plant cells –Cannot penetrate cell walls unless they are damaged –Spread by insects that feed on plants or by infected seeds

18 Retrovirus reproductive cycle –Reverse transcriptase catalyzes synthesis of DNA complementary to the viral RNA –Integrase integrates DNA into the host chromosome –Viral DNA used to transcribe viral RNA and synthesize proteins

19 Life cycle of HIV

20 Viroids –Short RNA strands with no protective coat –Cause plant diseases Prions –Only protein

21 Prokaryotes –No membrane-enclosed organelles such as nuclei or mitochondria

22 Common shapes –Cocci –Bacillus (rod-shaped) –Spirillum (rigid helix)

23 Micrococcus coccus bacteria

24 Salmonella bacilli bacteria

25 Spiroplasma spirilla bacteria

26 Cell walls in eubacteria –Gram-positive Very thick peptidoglycan –Gram-negative Thin layer of peptidoglycan Outer membrane –Capsule Surrounding the cell wall

27 Gram-positive cell wall

28 Gram-negative cell wall

29 Pili –Protein structures that extend from the cell –Help bacteria adhere to surfaces Flagella –Produce a rotary motion

30 Bacterial flagellum

31 Genetic material –Circular DNA molecule –Plasmids Asexual reproduction –Binary fission –Budding –Fragmentation

32 Transformation –Intake of DNA fragments Transduction –Phage carries bacterial DNA between cells Conjugation –Cells of different mating types

33 Transduction

34 Heterotrophs –Photoheterotrophs –Chemoheterotrophs Feed on dead organic matter Autotrophs –Photoautotrophs –Chemoautotrophs

35 Most bacteria are aerobic Faculatative anaerobes use oxygen if it is available Obligate anaerobes carry on metabolism only anaerobically

36 Domain Eubacteria Domain Archaea –Cell walls do not have peptidoglycan –Translation mechanisms similar to eukaryotes

37 Eubacteria and Archaea

38 Methanogens –Produce methane gas –Anaerobic environments Extreme halophiles –Inhabit saturated salt solutions Extreme thermophiles –Inhabit environments over 100°C

39 Vital ecological functions –Decomposers –Fixing nitrogen for plants Pathogens –Exotoxins –Endotoxins

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