December 4, 2009 Blog

Transduction- a virus that infects bacteria, bacteria goes into lytic/ lysogenic cycles

Conjugation- bacteria to bacteria. Sexpilus facilitates transfer of DNA; requires F plasmid

Transformation- bacteria receives DNA from the environment; requires plasmid, occurs under fixed conditions in laboratory

Transduction, conjugation, transformation: bacteria can evolve; DNA mutates

Lytic Cycle

• Lysis of host cell releases phages
• Destruction of host
• Production of new phages
• Temperate phage only

Lysogenic Cycle

• Can be induced to leave and enter lytic cycle
• Replicated and passed on
• Genome integrates into bacterial DNA (progphage)
• Virulent or temperate phage

Retroviruses

• RNA viruses
• Use reverse transcriptase (enzyme) to transcribe DNA from RNA template
• New DNA integrates into chromosome in nucleus of animal cell
• Host transcribes viral DNA into RNA

Example: HIV (no cure)

Viral diseases in animals

• Symptoms may be caused by
• Direct viral effect on cells
• Immune response of host
• Vaccines stimulate immune system to defend host against specific viruses

Prions

• Infectious proteins
• Misfolded proteins
• Cause misfolding of normal proteins

Virus

• Nucleic acid surrounded by protein coat
• Single or double-stranded
• RNA or DNA

Viroid

• Small, simple virus
• Circular RNA molecules
• Infect plants
• Do not encode proteins
• Naked nucleic acid

Gram +

• Bacteria with simple walls with a large amount of peptidoglycan
• Modified sugar polymers cross-linked with polypeptides
• Stain is not removed
• Dark violet or blue color

Gram –

• Less peptidoglycan
• Structurally more complex
• Outer membrane contains lipopolysaccharides
• Gram stain washes away
• Leaves pink or red cell

http://scienceblogs.com/retrospectacle/upload/2007/02/Prion2.gif