http://www.cellsalive.com/howbig.htm

Microbial Models: Genetics of Viruses and Bacteria 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 by capsid (protein coat) and sometimes a viral envelope (membrane surrounding)

The head of a dress-maker's pin can provide seating accommodation for five hundred million rhinoviruses (cause of the common cold) !

Why not alive? Lacks: nucleus, cytoplasm, organelles, cell membrane

obligate intracellular parasites Why not alive? No reproduction by mitosis No meiosis  (require a host cell in order to reproduce) obligate intracellular parasites

resistant to dehydration by osmosis obligate intracellular parasites Why not alive? Resistant to alcohol  resistant to dehydration by osmosis obligate intracellular parasites

cells cannot form crystals obligate intracellular parasites Why not alive? virus crystallization  cells cannot form crystals obligate intracellular parasites

Reproduction: 3 ways:

Lytic Cycle

Lytic Cycle “lock & key”

Lytic Cycle phage injects DNA (hopefully, for the virus, 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

Lysogenic Cycle temperate viruses

Lysogenic Cycle “phage” inserts DNA; via. “lock & key”

Lysogenic Cycle  encorporate into bacterial DNA via. crossing over

cellular division w/ a “friend” -replicates along with bacterial DNA) Lysogenic Cycle cellular division w/ a “friend” -replicates along with bacterial DNA)

Lysogenic Cycle at some point,  exits the chromosome, & initiates a LYTIC cycle

Lysogenic Cycle Phages manufactured BOOM!!

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

Why haven’t phages exterminated all bacteria? LYSOGENY

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

Envelope derived from nuclear membrane ex. of enveloped = herpes virus Reproduce in nucleus Envelope derived from nuclear membrane Typically, leave some DNA behind in nerve cells

ex. Herpes Simplex Type 1 (cold sore)

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   Viral Envelope   

RETROVIRUS ex. HIV

human immunodificiency virus

HIV   `   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

Viral Diseases Measles Polio Smallpox Influenza S.A.R.S. Bird flu

-Joshua Lederberg, Ph.D, Nobel laureate 1969 “The single biggest threat to man's continued dominance on the planet is the virus!” -Joshua Lederberg, Ph.D, Nobel laureate 1969 (won prize with Beadle and Tatum) Actually, he won the prize for discovering that bacteria can exchange genes… but what a great quote!

Mutations of existing virus EMERGING VIRUSES: HOW? HOW?HOW? HOW? BIRD FLU... where did we get it? Mutations of existing virus

Dissemination from a small, isolated population Increasing viral traffic ie. new roads can allow virus to spread between previously isolated areas Dissemination from a small, isolated population

Mutated form spread from animals

How to combate Virus? VACCINES - -*variants of pathogen *stimulates the immune system to “arm” and “defend”

Note: Can prevent some viral illnesses, Cannot cure the viral infection

Some viruses cause Cancer

Human papilloma virus

Viral nucleic acid becomes integrated into the hosts DNA Cancer

Proto-oncogenes code for proteins that affect the cell cycle. Cancer

Viroid- “naked” RNA *disrupt metabolism of plants stunts growth

Viroid- BIG NEWS b/c *molecules* can be an infectious agent and spread disease!

Prions- infectious. present in brain cells. misfolded proteins Prions- infectious *present in brain cells *misfolded proteins *converts “regular” proteins to prion version Mad cow disease