Viruses and Bacteria. Viral structure –DNA or RNA genome –Capsid Protein coat.
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Transcript of Viruses and Bacteria. Viral structure –DNA or RNA genome –Capsid Protein coat.
• Viruses are not cells
• Cannot metabolize independently
• Forces infected host cells to replicate viral DNA
• Takes over cell’s translation and transcription to reproduce
• Origin of viruses–Escaped gene hypothesis
• Viruses are often host species-specific
• Similarity of virus genome to host genome
• 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
• Lysogenic cycle–Usually does not kill the host–Viral genome replicated along with
host DNA• Attachment• Penetration• Integration• Replication
• Viral infection of animal cells–Surface attachment proteins bind
to specific cell receptors
–Fuse with plasma membrane
–Endocytosis
• Viral infection of plant cells– Cannot penetrate cell walls unless they are
damaged– Spread by insects that feed on plants or by
infected seeds
• 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
• Cell walls in eubacteria– Gram-positive
• Very thick peptidoglycan
– Gram-negative• Thin layer of peptidoglycan• Outer membrane
– Capsule• Surrounding the cell wall
• Pili– Protein structures that extend from the cell– Help bacteria adhere to surfaces
• Flagella– Produce a rotary motion
• Genetic material– Circular DNA molecule– Plasmids
• Asexual reproduction– Binary fission– Budding– Fragmentation
• Transformation– Intake of DNA fragments
• Transduction– Phage carries bacterial DNA between cells
• Conjugation– Cells of different mating types
• Heterotrophs– Photoheterotrophs– Chemoheterotrophs
• Feed on dead organic matter
• Autotrophs– Photoautotrophs– Chemoautotrophs
• Most bacteria are aerobic
• Faculatative anaerobes use oxygen if it is available
• Obligate anaerobes carry on metabolism only anaerobically
• Domain Eubacteria
• Domain Archaea– Cell walls do not have peptidoglycan– Translation mechanisms similar to eukaryotes
• Methanogens– Produce methane gas– Anaerobic environments
• Extreme halophiles– Inhabit saturated salt solutions
• Extreme thermophiles– Inhabit environments over 100°C