Virus Chapter 21

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microorganisms prokaryotic cells and single-celled protistans too small to be seen without the aid of a microscope.
What is the kingdom that contains the most individuals? prokaryotic
Pathogens infectious, diease causing agents that invade target organisms and multiply inside or on them.
Where do prokaryotic cells show the greatest diversity? in their means for securing resources
photoautotrophic species build organic compounds by photosynthesis, light driven self-feeders.
What is the energy and carbon source for photoautotrophic species? energy source is the sun and carbon source is Carbon dioxide,
What are the two places photoautotrophs may get their electrons and hydrogen? some get it from water molecules and release oxygen as a waste product. Others get them from inorganic compunds such as gaseous hydrogen and hydrogen sulfide.
chemoautotrophs self-feeders that use carbon dioxide as their carbon source.
Two different ways chemoautotrophs obtain required energy? Some oxidize organic compounds for energym others oxidize inorganic compunds such as iron, hydrogen, sulfur and nitrogen compounds.
Photoheterotrophs not self-feeders. They capture sunlight energy for photosynthesis. They get carbon from various organic compounds such as fatty acids and carbohydrates that other organisms produce.
Chemoheterotrophic prokaryotc cells parasites or saprobes, not self-feeders.
what is the difference between a saprobe and a parasite? a parasite draws glucose and other nutrients from a living host, where saprobes get nutrients by digesting organic products, wastes, or remains of other organisms.
the three shapes of bacteria coccus, bacillus, spirillum
coccus sphere
bacillus rod-shaped
spirillum spiral shaped
Prokaryotic means these cells were around before the evolution of the nucleated cell.
What is usually around the plasma membrane in prokaryotic cells? the cell wall
what is the purpose of the cell wall? This semi-rigid, permeable structure helps the cell maintain shape and resist rupturing when internal fluid pressures rise.
eubacterial cell walls are composed of... peptidoglycan
describe the structure of the peptiglycans: in these molecules, peptide groups crosslink many polysaccride strands to one another.
Gram stain a sample of unknown species is exposed to purple dye, then iodine, then an alcohol wash, then a counter stain.
what color represents Gram-positive? purple
what color represents Gram-negative? pink. Loses the purple during the wash, but the counter stain stains it pink.
glycocalyx a sticky mesh that often encloses the cell wall.
what is the glycocalyx composed of? polysaccrides, polypeptides, or both.
what does the glycocalyx look like when orgainized? Not organized? when organized, it forms a capsule. When not organized, it forms a slime layer.
what is the purpose of the glycocalyx? it helps a prokaryotic cell attach to teeth, mucous membranes, and other surfaces. Its also helps the cell avoid being phagocized by other cells that are usually fighting infection in their host cell.
bacterial flagella some species have one or more of these motile structures. They rotate like a propeller.
pili some species also have these short, filamentous proteins that project above the cell wall.
pupose of the pili? it helps the cells connect to each other for conjugation.
How do you measure the growth of prokaryotic cells? by increases of number of cells in a population.
what is different about the K12 strain of E. coli? it was the strain that was originally isolated from the human gut. It has been culticvated in the lab for so long that it is no longer able to grow when introduced into its natural habitat.
bacterial chromosome a circulized, double stranded DNA molecule that has only a few proteins attached to it.
prokaryotic fission the most common form of reproduction used by prokaryotic cells.
the steps of prokaryotic fission: 1) The bacterial chromosome is attached to the plasma membrane before DNA replication starts. 2) Replication starts and proceeds in both directions. 3) The DNA copy is attached at a membrane site of the parent DNA molecule. 4) the two DNA molecules are moved apart by membrane growth. 5) the two seperate cells now seperate from each other.
plasmid a small, self-replicating circle of extra DNA with a few genes.
F plasmid fertility plasmid. includes genes that confer the means to engage in a form of conjugation.
Describe how conjugation works: the F plasmid carries genetic information for synthesizing a structure called a sex pilus. The sex pili at the surface of the donor cell can hook to a recipient cell and pull it right up next to the donor. a conjugation tube forms between the two cells through which a plasmid DNA is transferred.
numerical taxonomy the traits of the unidentified cell are compared with those of a known prokaryotic group.
the types of traits looked at during numerical taxonomy: cell shape, motility, staining attributes of the cell wall, nutritional requirements, metabolic patterns and the presence or absence of endospores.
Another way to identify the relationship between two prokaryotic cells? nucleic acid hybridization between the rRNA.
eubacteria the most common prokaryotic cells (typical)
strain if two cells under study show only minor differences, one of them might be classified as a strain.
Three major groups of archeabacteria: extreme thermophiles, methanogensm and extreem halophiles.
extreme thermophiles heat lovers
where might you find extreme thermophiles? geothermally heated soils, hot springs, wastes from coal mines, etc.
what do extreme thermophiles use as their electron acceptor or donor? sulfur. (strict anaerobes)
solfolobus the first extreme thermophile discovered. grows in acidic hot springs.
Thermus aquaticus an extreme thermophile that biotechnologist utilize as a source of extremely heat-stable DNA polymerases.
methanogens (methane makers) live in oxygen free habitats, such as seamps, the guts of termites and mammals and stockyards. They are strict anaerobes and oxygen kills them.
how do methanogens produce ATP? by anaerobic ellctron transfer,
where do methanogens get their energy? They get electrons from hydrogen gas or from ethanol. they use carbon dioxide as their carbon source and as their final electron acceptor.
what do methanogens produce? methane
How much methane do methanogens produce? 2 billion tons per year.
how might methane from methanogens drastically alter the global climate in the future? If ocean circulation patterns change the huge methane deposits in the sea floor may be released all at once.
extreme halophiles salt lovers
How do extreme halophiles produce ATP? Most through aerobic pathways. When oxygen levels are low, they switch to photosynthesis.
What unique, light-absorbing pigment do extreme halophiles have under their plasma membrane? bacteriorholdopsin
what does the absorbtion of light energy do for the extreme halophiles? leads to an increase in H+ gradients across their plasma membrane. ATP forms when these ions follow their gradient and flow through the interior of transporter proteins, which span the membrane.
cyanobacteria once called blue-green algae, they are the classic example of photoautotrophic bacteria. Aerobic cells that engage in photosynthesis.
Anabaena Photoautotrophic bacteria. Convert nitrogen gas to ammonia for use in biosynthesis.
When are heterocysts formed? as nitrogen compounds dwindle, some of the photoautotrophic cells turn into these.
what are heterocysts? Cells that make a nitrogen-fixing enzyme. They synthesize and share nitrogen compounds with photosynthetic cells and in return they recieve carbohydrates.
Example of anaerobic photoautotrophs green bacteria
Where does green bacteria get its electrons? from hydrogen sulfide and hydrogen gas.
Chemoautotrophic bacteria Influence global cycling of nitrogen, sulfur and other nutrients. Nitrifying bacteria in the soil obtain electrons from ammonia.
What do chemoautotrophic bateria provide for plants? nitrate.
chemoheterotrophic bacteria nearly all known bacterial species are in this category. Many are decomposers.
Lactobacillus chemoheterotrphic bacteria. used to make pickles, buttermilk, sauerkraut, yogurt.
actinomycetes chemoheterotrophic bacteria. Sources of antibiotics.
E. coli chemoheterotrophic bacteria. Makes vitamin K and helps stop many food-borne pathogens from colonizing the gut.
Azospirillum chemoheterotrophic bacteria. Sugarcane and corn benefit from this nitrogen-fixing sirochete.
Deinococcus radiodurans chemoheterotrophic bacteria. resists high radiation doses that kill other species.
Deinococcus radiodurans chemoheterotrophic bacteria. resists high radiation doses that kill other species.
Some examples of pathogenic chemoheterotrophic bacteria? E. coli (causes a form of diarrhea that is the main cause of infant death in developing countries), Clostridium botulinum (a food taint whose toxins cause botulism). C. tetani (causes the diease tetanus)
How does the C. tetani work? It can form an endospore.
endospore This resting structure forms inside the cell, around one copy of the bacterial chromosome and part of the cytoplasm. Endospores form when a depletetion of nitrogen arrests cell growth. They are released as free spores when the plasma membrane erupts.
Why are endospores so dagerous? They are resistant to heat, drying out, irradiation, acids, disinfectanats, and boiling water. They can stay dormant, in some cases, for many decades.
Examples of pathogenic chemoheterotrophic bacteria that travels from host to host in the gut of insects: Borrelia burgdorferi (causes lyme disease) Rickettsia rickettsii (causes Rocky Mountain Fever)
Describe what happens to you when you are bitten by a tick that has Rickettsia rickettsii in its gut: After the bacterium enters the host, it penetrates the cytopasm and nucleus of the hosts cells. 3-12 days later, a fever and severe headache develop. 3-5 days later, a rash appears on extremities. Diarrhea and gastrointestinal cramps are common.
What facts point to the idea that bacteria are small but not simple? Their behavior. They will move toward nutrient-rich regions. Aerobes move toward oxygen, and anaerobes move away from it. photosynthetic types move toward light, but will move away if the light gets too intense.
Magnetotactic bacteria contain a chain of magnetite particles that serve as a tiny compass which helps them sense which way is north and also down. They swim towards the bottom of a body of water, where oxygen levels are lower and therefore more suitable for their growth.
An example of collective behavior of bacteria: millions of Myxococcus xanthus cells form a predatory colony. These cells secrete an enzyme that digests prey such as syanobacteria, that become stuck to the colony. Bacteria have also been known to migrate together, then all change direction to move toward a food source.
fruiting bodies spore-bearing structures
how do Myxobacteria form fruiting bodies? some cells in the colony differntiate and form a slime stalk, others form branches, and others form clusters of spores. The spores disperse when a cluster bursts open, each may give rise to a new colony.
what does the word virus mean? poison or venomous secretion
What is a virus? A noncellular infectious agent that has two characteristics. 1) a viral particle consists of a protein coat wrapped around a nucleic acid core (its genetic material) and 2) It can be reproduces only after its genetic material enters a host cell.
Is the genetic material in a virus DNA or RNA? It can be either.
What is the purpse of the protein coat around the virus? It helps protect the genetic material on the journey to the host cell. Its contains proteins that can bind with specific receptors on host cells. It also contains spikes of glycoproteins, which spike when a predator tries to engulf it.
How can viruses often avoid immune fighters? Their genes mutate at high frequencies. That is why the flu shot is different every year.
What do we study to learn more about viruses? bacteriophages
Why is it almost impossible to study the virus itself? Because each kind of virus can multiply only in certain hosts. It cannot be studied easily unless the investigator cultures living hosts.
bacteriophages a group of viruses that infect bacterial cells.
How big are animal viruses? They range in size from parvoviruses (18 nanometers) to brick-shaped poxviruses (350 nanometers).
What obstacles must viruses overcome in order to infect a plant? How do they overcome this obstacle? They must first breach the cell wall. They typically hitch rides on the piercing or sucking devices of insects that feed on insect juices.
Example of a virus that infects plants? tobacco mosaic virus (RNA virus)
What are the four steps all viruses go through when they multiply? 1) Attachment 2) Penetration 3) replication and synthesis 4) assembly
At what stage does the way viruses multiply branch into two different paths? at step 5, Release.
Attachment stage of viral multiplication: A virus attaches to a host cell by molecular groups that can chemically recognize and lock on to specific molecular groups at the cells surface.
Penetration stage of viral multiplication: Either the whole virus or its genetic material alone penetrates the cells cytoplasm.
Replication and synthesis stage of viral multiplication: In an act of molecular piracy, the viral DNA or RNA directs the host cell into producing many copies of the viral nucleic acids and viral proteins, including enzymes.
Assembly stage of viral multiplication: The viral nuceic acids and viral proteins become organized as new infectious particles.
Lytic pathway: Steps 1-4 proceed rapidly, and new particles are released when a host cell undergoes lysis.
Lysongenic pathway A latent period extents the cycle. The virus doesn't kill the host cell outright. a viral enzyme cuts the host chromosome, then integrates viral genes into it. When the infected cells prepares to divide, it replicates the recombinant molecule. Miniature time bombs are passed on to all of the cells descendants. Later on, a molecular signal of some other stimulus may reactivate the cycle.
An example of a virus that has a latency period: Type I herpes simplex virus. Almost everyone harbors this virus, it remains latent in facial tissues inside a ganglion. Sunburn and other stress factors can make it come out.
Example of a retrovirus and how it works: HIV. Carts its own enzymes into ells. These assemble Dna on viral RNA by reverse transcriptase.
Viroids tightly folded strands or circles of RNA are smaller than anything in viruses. They too cause infections even though they do not have protein-coding genes.
do viroids have a protein coat? no, but the tight folding might help protect them from the hosts enzymes.
What are some theories about where viroids come from? They resemble introns (the noncoding portions of eukaryotic DNA). They might be self-splicing introns that escaped from DNA molecules. Or they may be remnants left over from an ancient RNA world.
Prions are largely, if not entirely, abnormal, less soluble forms of proteins necessary for the operation of neurons (the communication cells of the nervous system).
what do prions do? They catalyze the conversion of the normal proteins into more prions. They coagulate as massive deposits inside the brain and cause fatal degenerative diseases.
Creutzfeldt-Jakob disease disease that progressively destroy muscle coordination and brain function. Caused by prions.
scrapie a prion-linked disease of sheep. The sheep scratch themselves against trees or posts until all of their wool is gone.
BSE Bovine spongiform encephalopathy. (mad cow disease) Prion-linked.
How did the first case of BSE come about? Sheep with scrapie were ground up and feed to cows.
infection when a pathogen invades yout body, multiplies in cells and tissues.
disease the outcome of infection. occurs when defenses cannot be mobilized fasr enough to keep the pathogens activities from interfering with body functions.
epidemic a disease spreads fast through part of a population for a limited time, then subsides.
pandemic If an epidemic breaks out in several countries at the same time (example: AIDS)
Sporadic diseases (such as whooping cough) occur irregularly and effect few people.
Endemic diseases pop up more or less continuously but do not spread far in large populations. (example: T.B. and impetigo)
Two barriers that prevent pathogens from evoloving into a position of world dominance: any species with a history of being attacked by a certain pathogen has coevolved with it and has built defenses against it. And if a pathogen kills too quickly, it might disappear along with the host.
When will a pathogen cause an individual to die? only if it becomes host to overwhelming number of pathogens, if it is a novel host with no coevolved defenses, or if a mutant pathogenic strain has emerged and has breached current defenses.
emerging pathogens have been around for a long time and are only now taking advantage of the presence of novel human hosts. Others are newly mutated strains of existing pathogens.
Ebola one of several viruses that cause a deadly hemorrhagic fever. It may have coevolved with monkeys in africa tropical forests. By 1976, it was infecting humans.
monkeypox virus a relative of the smallpox virus. after infecting its host, this DNA virus replicates in bone marrow, the lymph nodes and the spleen. The blood stream transports new viral particles to the skin where they cause large, hardened pus-filled sores.