Ch 18 Microbial Models: Genetics of Viruses and Bacteria
smaller than ribosomes!
S.A.R.S. HIV Ebola Polio Bird Flu Meningitis chicken pox
Virus- *biological particle(not a cell) *composed of nucleic acid (RNA or DNA)
Virus- *surrounded bycapsid(protein coat)and sometimes aviralenvelope(membrane surrounding)
The head of a dress-maker's pin can provide seating accommodation for fivehundredmillion rhinoviruses (cause of the common cold) !
Why not alive? • Lacks: nucleus, cytoplasm, organelles, cell membrane
Why not alive? • No reproduction by mitosis No meiosis (require a host cell in order to reproduce) obligateintracellularparasites
Why not alive? • Resistant to alcohol resistant to dehydration by osmosis obligateintracellularparasites
Why not alive? • virus crystallization cells cannot form crystals obligateintracellularparasites
Reproduction: 3 ways:
Lytic Cycle “lock & key”
Lytic Cycle phage injects DNA (hopefully, forthevirus, it is resistant to the restriction nucleases!)
Lytic Cycle phage DNA hydrolysises bacterial DNA via. enzymes
Lytic Cycle phage proteins are produced, phage DNA reproduced
Lytic Cycle host cell provides: nucleotides, ribosomes, tRNA etc.
Lytic Cycle Lysozyme produced and bacterial wall is digested
Lytic Cycle BOOM!!
Lytic Cycle virulent virus
Lysogenic Cycle “phage” inserts DNA; via. “lock & key”
Lysogenic Cycle encorporate into bacterial DNA via. crossing over
Lysogenic Cycle cellular division w/ a “friend” -replicates along with bacterial DNA)
Lysogenic Cycle at some point, exits the chromosome, & initiates a LYTIC cycle
latent/ temperate virulent
Why haven’t phages exterminated all bacteria? • Restriction Enzymes in bacteria • Methylation of bacterial DNA prevents the restriction enzyme from attacking its own self
Why haven’t phages exterminated all bacteria? • Natural Selection favors the mutant bacteria w/ protein receptors that have an altered shape • no longer recognizable by phage
variations of viral reproduction
Viruses are Classified as: 1. DNA viruses 2. RNA viruses
Viruses are Classified as: 1. membranous envelope present 2. membranous envelope absent
ex.of enveloped = herpes virus Reproduce in nucleus Envelope derived from nuclear membrane Typically, leave some DNA behind in nerve cells
Herpes Viruses • Use nuclear membrane to derive new envelope. • Viral DNA integrated into Host DNA as a provirus. • Shows both lytic and lysogenic life cycles.
does not kill host Viral Envelope
HIV ` host is a WBC called a T-cell
http://www.youtube.com/watch?v=B7ITZgag6w0&feature=related http://www.youtube.com/watch?v=dyxujBKHdWc http://www.youtube.com/watch?v=9leO28ydyfU&NR=1
HIV needs to connect to TWO protein types on the outside of the Immune System’s Helper T Cells
HIV needs to connect to TWO protein types on the outside of the Immune System’s Helper T Cells (WBC)
LAST KIND • DNA
DNA Viruses 1.Insert their DNA into host/ the host produces mRNA compliment 2.Production of new viral proteins, or join with the DNA of the host cell 3.Directs production of new viruses
viral DNA replicated uses it to enter host DNA capsid removed genetic material duplicated