Biodiversity: prokaryotes & viruses
All three domains contain microscopic organisms. Focus now: Prokaryotes
Prokaryotes in general Asexual, single-celled, no nucleus or organelles, circular DNA Can live as single cells or in colonies Diverse & widespread Found on & in multicellular organisms Found in habitats too extreme for eukaryotes to survive Includes the Domains bacteria & archaea Bacteria on the point of a pin, magnified 650x
Domain Bacteria Bacteria cause about ½ of all human diseases BUT, less than 1% of bacteria cause disease There are far more benign or beneficial bacteria decompose dead organisms & other organic waste material important in all chemical cycles (C, N & P) help us digest & gain vitamins from our food give taste to many foods (sour cream, yogurt, sourdough bread, more) used in biotechnology...
Characteristics used to classify Domain Bacteria Shape of cell Characteristics of cell wall Modes of nutrition
Shape of cells Cocci (round) Bacilli (rod) Spirochete (spiral)
Characteristics of bacteria cell wall Two types of cell walls; use a Gram stain to identify type Gram + simpler walls with relatively thick layer of peptidoglycan Gram more complex walls with peptidoglycan and glycolipids Important medicinally to identify type of cell wall; Gram are harder to treat with antibiotics & the lipids are often toxic
Modes of Nutrition ( trophs ) Organotrophs organic feeders consume organic molecules as source of energy ex. carbohydrates Lithotrophs rock feeders consume inorganic molecules for source of energy ex. ammonia, hydrogen sulfide, iron Photoautotrophs light self feeders use light as source of energy bacteria have chlorophyll to carry out photosynthesis to make glucose
Characteristics of Domain Archaea Were classified as bacteria until DNA analysis showed they are vastly different differences in composition of plasma membranes, cell walls & flagella Cell walls contain polysaccharides not found in bacteria or eukaryotes Several antibiotics have no effect on growth Some enzymes & ribosomes similar to eukaryotes Habitats help classify can thrive in extreme temperatures, salt, ph, pressure (extremophiles) can live in not-so extreme habitats too, including in humans
Archaea are more closely related to eukaryotes than to bacteria
What about viruses? It s not a cell... nucleic acid enclosed in a protein coat (capsid) some have a few enzymes some have an outer envelope with glycoproteins that helps virus enter & leave cell no metabolic processes* no movement of particles into or out of capsid to alter internal environment basically parasites that can only reproduce in a host cell host cells provide most of the resources for replicating, transcribing & translating viral nucleic acid
Two kinds of viruses DNA viruses the nucleic acid in the capsid is DNA relatively stable viruses; do not rapidly evolve allows vaccination to last years ex. in animals: hepatitis, chicken pox, small pox, herpes RNA viruses the nucleic acid in the capsid is RNA called retroviruses b/c they transcribe DNA from RNA...!! evolve quickly b/c they lack proofreading mutation-catching enzymes of DNA replication difficult to treat ex. in animals: common cold, flu, measles, mumps, AIDS, Ebola
Who is at risk? Practically everything; viruses can infect animals, plants & bacteria most infect just one species or only a few closely related species & enter only one kind of cell in that species measles virus only infects humans rabies virus can infect all mammals some can infect a wide range of hosts West Nile virus can infect mosquitoes, birds, horses, & humans glycoproteins on virus surface determine which host can be infected and which cells it can enter no cure for most viral infections
(In general) How viruses replicate viral genome enters host cell; mechanism varies by virus host enzymes replicate viral genome host enzymes transcribe viral genome into viral mrna; host ribosomes translate into capsid proteins replicated viral genomes & capsid proteins self-assemble into new virus particles that leave the cell mechanism varies by virus
So where should we put viruses? Next time Eukaryotic origins & Fungi