Biology chapters 19 and 27
How are viral infections limited to some cell types or species types?
"lock-and-key" fit: how viruses identify host cells; used between viral surface proteins and specific receptor molecules on the outside of cells (portal of entry)
epidemic
-a general outbreak of a disease or widespread occurrence of an infectious disease in a community at a particular time -a general outbreak of a flu-like illness appeared in Mexico and the United States, caused by an influenza virus named H1N1 oFlu caused by new strains of influenza virus to which people have little immunity
motility of bacteria
-bacteria propel themselves by flagella scattered about the surface or concentrated at one or both ends -Flagella of bacteria, archaea, and eukaryotes are composed of different proteins and likely evolved independently
Tobacco Mosaic Virus
-stunts growth of tobacco plants and gives their leaves a mosaic coloration -has a rigid, rod-shaped capsid
A
12.What are prions? A)misfolded versions of normal brain protein B)tiny molecules of RNA that infect plants C)viral DNA that has had to attach itself to the host genome D)viruses that invade bacteria E)a mobile segment of DNA
B
12.Which statement about gram-negative bacteria is correct? A)Penicillins are the best antibiotics to use against them. B)They often possess an outer membrane containing toxic lipopolysaccharides. C)Their chromosomes are composed of DNA tightly wrapped around large amounts of D)histone proteins. E)Their cell walls are primarily composed of peptidoglycan.
B
19.Mycoplasmas are bacteria that lack cell walls. On the basis of this structural feature, which statement concerning mycoplasmas should be true? A) They are gram-negative. B) They are subject to lysis in hypotonic conditions. C) They lack a cell membrane as well. D) They undergo ready fossilization in sedimentary rock. E) They possess typical prokaryotic flagella.
B
24.Penicillin is an antibiotic that inhibits enzymes from catalyzing the synthesis of peptidoglycan, so which prokaryotes should be most vulnerable to inhibition by penicillin? A) mycoplasmas B) gram-positive bacteria C) archaea D) gram-negative bacteria E) endospore-bearing bacteria
A
24.Which of the following is the best predictor of how much damage a virus causes? A) ability of the infected cell to undergo normal cell division B) ability of the infected cell to carry on translation C) whether the infected cell produces viral protein D) whether the viral mRNA can be transcribed E) how much toxin the virus produces
B
25.Antiviral drugs that have become useful are usually associated with which of the following properties? A) ability to remove all viruses from the infected host B) interference with the viral reproduction C) prevention of the host from becoming infected D) removal of viral proteins E) removal of viral mRNAs
Viruses
8.What did Wendell Stanley discover?
Tobacco mosaic virus
9.What VIRUS DID Wendell Stanley discover?
B
9.Which of the following use light energy to generate ATP, but do not release oxygen? A)photoautotrophs B)photoheterotrophs C)chemoautotrophs D)chemoheterotrophs that perform decomposition E)parasitic chemoheterotrophs
viral genome organization
----usually organized as a single linear or circular molecule of a nucleic acid, even though the genomes of some viruses consist of multiple molecules of nucleic acid ----Can contain 4 to 1,000 genes in their genome
F factor
-A piece of DNA is required to produce pili •absence of this in cells act DNA recipients during conjugation •transferable during conjugation
Why are viral infections limited to some cell types or species types?
-Results from the evolution of recognition systems by the virus -Viral infection of multicellular eukaryotes is limited to particular tissues (cold virus infects cells lining the upper respiratory tract and AIDS virus binds to receptors only present on white blood cells)
D
A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. 53) This bacterium's ability to survive in a human who is taking penicillin pills may be due to the presence of 1. penicillin-resistance genes 2. a secretory system that removes penicillin from the cell 3. a gram-positive cell wall 4. a gram-negative cell wall 5. an endospore A) 1 or 5 B) 2 or 3 C) 4 or 5 D) 2, 3, or 5 E) 2, 4, or 5
D
Although not present in all bacteria, this cell covering often enables cells that possess it to resist the defenses of host organisms, especially their phagocytic cells. A) endospore B) sex pilus C) cell wall D) capsule
transformation
A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment
photoautotroph
An organism that harnesses light energy to drive the synthesis of organic compounds from carbon dioxide or bicarbonate (ex. Cyanobacteria)
chemoautotroph
An organism that obtains energy by oxidizing inorganic substances and needs only carbon dioxide (or bicarbonate) as a carbon source (unique to certain prokaryotes, Sulfolobus)
chemoheterotroph
An organism that requires organic molecules for both energy and carbon (many prokaryotes (Clastridium); protists; fungi; animals; and some plants)
photoheterotroph
An organism that uses light to generate ATP but must obtain carbon in organic form (unique to certain aquatic and salt-loving prokaryotes Rhodobacter, Chloroflexus)
B
Prokaryotes' essential genetic information is located in the A) nucleolus. B) nucleoid. C) nucleosome. D) plasmids. E) exospore.
E
In a bacterium that possesses antibiotic resistance and the potential to persist through very adverse conditions, such as freezing, drying, or high temperatures, DNA should be located within, or be part of, which structures? 1. nucleoid region 2. endospore 3. fimbriae 4. plasmids A) 1 only B) 1 and 2 only C) 1 and 4 only D) 2 and 4 only E) 1, 2, and 4
E
Mitochondria are thought to be the descendants of certain alpha proteobacteria. They are, however, no longer able to lead independent lives because most genes originally present on their chromosome have moved to the nuclear genome. Which phenomenon accounts for the movement of these genes? A) plasmolysis B) conjugation C) translation D) endocytosis E) horizontal gene transfer
Rhizobium, that bio luminescence bacteria in the headlight fish, Heterocysts, 500 to 1000 prokaryotes in our gut
NAME FOR ME A BACTERIAL EXAMPLE OF MUTUALISM
A
Prokaryotic ribosomes differ from those present in eukaryotic cytosol. Because of this, which of the following is correct? A) Some antibiotics can block protein synthesis in bacteria without effects in the eukaryotic host. B) Eukaryotes did not evolve from prokaryotes. C) Translation can occur at the same time as transcription in eukaryotes but not in prokaryotes. D) Some antibiotics can block the synthesis of peptidoglycan in the walls of bacteria. E) Prokaryotes are able to use a much greater variety of molecules as food sources than can eukaryotes.
B
RNA viruses require their own supply of certain enzymes because A) host cells rapidly destroy the viruses. B) host cells lack enzymes that can replicate the viral genome. C) these enzymes translate viral mRNA into proteins. D) these enzymes penetrate host cell membranes. E) these enzymes cannot be made in host cells.
Transformation, Transduction, Conjugation
THREE PROCESSES THAT CAUSE GENETIC RECOMBINATION?
to protect from cytolyzing of a cell due to hypotonic environment
WHAT IS THE Function of the cell wall in prokaryotic cells?
Myxoplasma (doesn't gram stain)
WHAT IS THE NAME OF THE SMALLEST PROKARYOTE?
750 microns µm
WHAT IS THE SIZE OF THE LARGEST PROKARYOTE FOUND? (proper units are necessary)
They are all gram negative
WHAT IS the ONE UNIFYING FEATURE THAT ALL PROTEOBACTERIA HAVE IN COMMON (THE ANSWER IS NOT that they are BACTERIA)
Peptidoglycan
WHAT STRUCTURAL ELEMENT IN THE CELL WALL SEPARATES BACTERIA FROM THE OTHER TWO DOMAINS?
It shrivels - loses water to the external environment
What happens when a prokaryotic cell plasmolyzes?
B
What is the function of reverse transcriptase in retroviruses? A) It hydrolyzes the host cell's DNA. B) It uses viral RNA as a template for DNA synthesis. C) It converts host cell RNA into viral DNA. D) It translates viral RNA into proteins. E) It uses viral RNA as a template for making complementary RNA strands.
Defense against viral genetic material
What purpose does a restriction enzyme play within a cell?
C
Which of the following characteristics, structures, or processes is common to both bacteria and viruses? A) metabolism B) ribosomes C) genetic material composed of nucleic acid D) cell division E) independent existence
C
Which of these statements about prokaryotes is correct? A) Bacterial cells conjugate to mutually exchange genetic material. B) Their genetic material is confined within vesicles known as plasmids. C) They divide by binary fission, without mitosis or meiosis. D) The persistence of bacteria throughout evolutionary time is due to their genetic homogeneity (in other words, sameness). E) Genetic variation in bacteria is not known to occur, because of their asexual mode of reproduction.
A
Which statement about the domain Archaea is true? A) Genetic prospecting has recently revealed the existence of many previously unknown archaean species. B) No archaeans can reduce CO₂ to methane. C) The genomes of archaeans are unique, containing no genes that originated within bacteria. D) No archaeans can inhabit solutions that are nearly 30% salt. E) No archaeans are adapted to waters with temperatures above the boiling point.
E
Which statement about the genomes of prokaryotes is correct? A) Prokaryotic genomes are diploid throughout most of the cell cycle. B) Prokaryotic chromosomes are sometimes called plasmids. C) Prokaryotic cells have multiple chromosomes, "packed" with a relatively large amount of protein. D) The prokaryotic chromosome is not contained within a nucleus but, rather, is found at the nucleolus. E) Prokaryotic genomes are composed of circular DNA.
B
Which two structures play direct roles in permitting bacteria to adhere to each other, or to other surfaces? 1. capsules 2. endospores 3. fimbriae 4. plasmids 5. flagella A) 1 and 2 B) 1 and 3 C) 2 and 3 D) 3 and 4 E) 3 and 5
E
Which viruses have single-stranded RNA that acts as a template for DNA synthesis? A) lytic phages B) proviruses C) viroids D) bacteriophages E) retroviruses
B
Why do RNA viruses appear to have higher rates of mutation? A) RNA nucleotides are more unstable than DNA nucleotides. B) Replication of their genomes does not involve proofreading. C) RNA viruses replicate faster. D) RNA viruses can incorporate a variety of nonstandard bases. E) RNA viruses are more sensitive to mutagens.
"resistance genes"
code for enzymes that specifically destroy or hinder the effectiveness of certain antibiotics; carried by R plasmids
flagellum
composed of a motor, hook, and filament; Many of the proteins are modified versions of proteins that perform other tasks in bacteria; likely evolved as existing proteins were added to an ancestral secretory system
pandemic
a global epidemic oThe 2009 flu likely passed to humans from pigs; for this reason it was originally called the "swine flu"
viral envelope composition
contain a combination of viral origin (proteins and glycoproteins) and host cell molecules (phospholipids and membrane proteins)
Helical viruses
contains over a thousand molecules of a single-type of protein arranged in a helix; rod-shaped capsid
temperate phage
a phage that is capable of replicating by either a lytic or lysogenic cycle
virulent phage
a phage that only replicates by the lytic cycle
viroids
a plant pathogen consisting of a molecule of naked, circular RNA a few hundred nucleotides long; disrupt plant growth
nucleiod
a region of cytoplasm that appears lighter than the surrounding cytoplasm in electron micrographs
symbiosis
an ecological relationship in which two species live in close contact: a larger host and smaller symbiont; prokaryotes often form symbiotic relationships with larger organisms
gram-negative
less peptidoglycan and an outer membrane that can be toxic; likely to be antibiotic resistant; cell appears pink or red due to red safranin dye
slime wall
less well organized sticky layer of polysaccharide or protein layer
extreme halophiles
live in highly saline environments
rod-shaped, polyhedral, or more complex
different capsid structures
heterocysts
filament cell that carries out nitrogen fixation; surrounded by a thick cell wall that restricts entry of O2 produced by neighboring photosynthetic cells; transport fixed nitrogen to neighboring cells and to receive carbohydrates
Wendell M. Stanley
first to discover and crystallize a virus discovered the tobacco mosaic virus
pili (sex pili)
hair like appendages longer than fimbriae; pull two cells together prior to DNA transfer from one cell to the other
fimbriae
hair like appendages that allow them to stick to their substrate or other individuals in a colony; only some prokaryotes have them
vertical transmission
inheriting the virus from a parent; can occur in asexual propagation (cuttings) or in sexual reproduction via infected seeds
biofilms
metabolic cooperation occurs in these surface-coating colonies; secrete signaling molecules that recruit nearby cells that cause colonies to grow; produce polysaccharides and proteins that stick the cells to the substrate and to one another; channels allow nutrients to reach cells in the interior and wastes to be expelled
obligate anaerobes
poisoned by O2; live exclusively by fermentation or extract energy by anaerobic respiration
mutation
rates during binary fission are low, but because of rapid reproduction, can accumulate rapidly in a population
methanogens
release methane as a by-product of their unique ways of obtaining energy; strict anaerobes and are poisoned by O2; use CO2 to oxidize H2 (produces energy and methane waste); live in swamps and marshes or under ice
gram-positive
simpler walls with a large amount of peptidoglycan; crystal violet is not stripped by alcohol, so the stain appears blue
plasmids
smaller rings of replicating DNA molecules
transduction
the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)
chemotaxis
the movement toward or away from a chemical stimulus
AIDS (acquired immunodefiency syndrome)
the symptoms and signs present during the late stages of HIV infection, defined by a specified reduction in the number of T cells and the appearance of characteristic secondary infections
extreme thermophiles
thrive in very hot environments
binary fission
•A single prokaryotic cell divides into 2 cells, which then divide into 4, 6, 8... cells •Prokaryotes can divide every 1-3 hours under optimal conditions •a new species can be produced in 20 minutes
restriction enzymes
•an endonuclease that recognizes and cuts DNA molecules foreign to a bacterium (such as phage genomes) •cuts at specific nucleotide sequences (restriction sites) •main defense against phages
prions
•an infectious agent that is a misfolded version of a normal cellular protein •increase in number by converting correctly folded versions of the protein to more prions •Scrapie in sheep, mad cow disease, and Creutzfeldt-Jakob disease in humans are all caused by prions
gram staining
•classify bacteria by cell wall composition; used by scientists; developed by Hans Christian Gram •Process: samples are stained with crystal violet dye and iodine, then rinsed in alcohol, and then stained with a red dye such as safranin
capsule
•dense and well-defined polysaccharide or protein layer that covers many prokaryotes •can protect against dehydration and host immune systems; enables prokaryotes to adhere to their substrate or to other individuals in a colony
chlamydia
•parasites that live within animal cells and depend on hosts for resources like ATP; •gram-negative walls lack peptidoglycan •trachomatis causes blindness and nongonococcal urethritis by sexual transmission
cyanobacteria
•photoautotrophs that generate O2 •self-sufficient and only need light, CO2, N2, water, and some minerals to grow •Solitary and filamentous are abundant components of freshwater and marine phytoplankton •Use nitrogen fixation
endospores
•resistant cells that are metabolically inactive and can remain viable in harsh conditions for centuries •original cell produces a copy of its chromosome and surrounds it with a tough multilayered structure •if water is removed, metabolism halts (can resume when environment improves) •the original cell lyses and cels releases
The 3 ways viruses cause disease
1) Viruses may damage or kill cells by causing the release of hydrolytic enzymes from lysosomes 2) Some viruses cause infected cells to produce toxins that lead to disease symptoms 3) Others have molecular components such as envelope proteins that are toxic
D
23.Which of these is the most common compound in the cell walls of gram-positive bacteria? A) cellulose B) lipopolysaccharide C) lignin D) peptidoglycan E) protein
B
1.Which of the following represents a difference between viruses and viroids? A)Viruses cannot pass through plasmodesmata; viroids can. B)Viruses infect many types of cells, whereas viroids infect only plant cells. C)Viruses have capsids composed of protein, whereas viroids are only capsid without genetic material. D)Viruses contain introns; viroids have only exons. E)Viruses always have genomes composed of DNA, whereas viroids always have genomes composed of RNA.
D
10.Which of the following is characteristic of the lytic cycle? A)Many bacterial cells containing viral DNA are produced. B)Viral DNA is incorporated into the host genome. C)The viral genome replicates without destroying the host. D)A large number of phages is released at a time. E)The virus-host relationship usually lasts for generations.
Methylation
11.WHAT PROCESS PREVENTS RESTRICTION ENZYMES FROM DESTROYING BACTERIAL DNA?
B
13.The host range of a virus is determined by WHAT? A)whether its nucleic acid is DNA or RNA. B)the proteins on its surface and that of the host. C)the proteins in the hostʹs cytoplasm. D)the enzymes produced by the virus before it infects the cell. E)the enzymes carried by the virus.
E
14.Which of the following molecules make up the viral envelope? A)carboproteins B)proteosugars C)carbopeptides D)peptidocarbs E)glycoproteins
E
15.AN ORGANISM WITH LEPROSY IS ANALYSED HISTOLOGICALLY, WHAT IS VISUALLY SEEN? A) GRAM + (staining purple B) GRAM - (straining pink) C) GRAM + (staining pink) D) GRAM - (staining purple) E) None of the Above
A
15.Why are viruses referred to as obligate parasites? A) They cannot reproduce outside of a host cell. B) Viral DNA always inserts itself into host DNA. C) They invariably kill any cell they infect. D) They can incorporate nucleic acids from other viruses. E) They must use enzymes encoded by the virus itself.
A
16.Most human-infecting viruses are maintained in the human population only. However, a zoonosis is a disease that is transmitted from other vertebrates to humans, at least sporadically, without requiring viral mutation. Which of the following is the best example of a zoonosis? A) rabies B) herpesvirus C) smallpox D) HIV E) hepatitis virus
Rapid Reproduction, mutations, genetic recombination
16.WHAT ARE THE THREE FEATURES THAT ADD TO PROKARYOTIC GENETIC DIVERSITY?
C
17. Which of the following statements describes the lysogenic cycle of lambda (_) phage? A) After infection, the viral genes immediately turn the host cell into a lambda-producing factory, and the host cell then lyses. B) Most of the prophage genes are activated by the product of a particular prophage gene. C) The phage genome replicates along with the host genome. D) Certain environmental triggers can cause the phage to exit the host genome, switching from the lytic to the lysogenic. E) The phage DNA is incorporated by crossing over into any nonspecific site on the host cell's DNA.
Instructions for sex pili
17.WHAT IS AN F PLASMID?
biofilm
18.A term describing Many prokaryotes living together acting in ways that individually would be impossible?
B
18.Why do RNA viruses appear to have higher rates of mutation? A) RNA nucleotides are more unstable than DNA nucleotides. B) Replication of their genomes does not involve the proofreading steps of DNA replication. C) RNA viruses replicate faster. D) RNA viruses can incorporate a variety of nonstandard bases. E) RNA viruses are more sensitive to mutagens.
E
19. Most molecular biologists think that viruses originated from fragments of cellular nucleic acid. Which of the following observations supports this theory? A) Viruses contain either DNA or RNA. B) Viruses are enclosed in protein capsids rather than plasma membranes. C) Viruses can reproduce only inside host cells. D) Viruses can infect both prokaryotic and eukaryotic cells. E) Viral genomes are usually more similar to the genome of the host cell than to the genomes of viruses that infect other cell types.
B
20.Though plants, fungi, and prokaryotes all have cell walls, we place them in different taxa. Which of these observations comes closest to explaining the basis for placing these organisms in different taxa, well before relevant data from molecular systematics became available? A) Some closely resemble animals, which lack cell walls. B) Their cell walls are composed of very different biochemicals. C) Some have cell walls only for support. D) Some have cell walls only for protection from herbivores. E) Some have cell walls only to control osmotic balance.
A
20.What is the name given to viruses that are single-stranded RNA that acts as a template for DNA synthesis? A) retroviruses B) proviruses C) viroids D) bacteriophages E) lytic phages
A
21.Which is the bacterial structure that acts as a selective barrier, allowing nutrients to enter the cell and wastes to leave the cell? A) plasma membrane B) capsule C) cell wall D) nucleoid region E) pili
A
21.Which of the following can be effective in preventing viral infection in humans? A) getting vaccinated B) taking nucleoside analogs that inhibit transcription C) taking antibiotics D) applying antiseptics E) taking vitamins
B
22.Which of the following describes plant virus infections? A) They can be controlled by the use of antibiotics. B) They are spread throughout a plant by passing through the plasmodesmata. C) They have little effect on plant growth. D) They are seldom spread by insects. E) They can never be inherited from a parent.
C
22.Which statement about bacterial cell walls is false? A) Bacterial cell walls differ in molecular composition from plant cell walls. B) Cell walls prevent cells from bursting in hypotonic environments. C) Cell walls prevent cells from dying in hypertonic conditions. D) Bacterial cell walls are similar in function to the cell walls of many protists, fungi, and plants. E) Cell walls provide the cell with a degree of physical protection from the environment.
A
23.The difference between vertical and horizontal transmission of plant viruses is that A) vertical transmission is transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant. B) vertical transmission is the spread of viruses from upper leaves to lower leaves of the plant, and horizontal transmission is the spread of a virus among leaves at the same general level. C) vertical transmission is the spread of viruses from trees and tall plants to bushes and other smaller plants, and horizontal transmission is the spread of viruses among plants of similar size. D) vertical transmission is the transfer of DNA from one type of plant virus to another, and horizontal transmission is the exchange of DNA between two plant viruses of the same type. E) vertical transmission is the transfer of DNA from a plant of one species to a plant of a different species, and horizontal transmission is the spread of viruses among plants of the same species.
A
25.Jams, jellies, preserves, honey, and other foodstuffs with a high sugar content hardly ever become contaminated by bacteria, even when the food containers are left open at room temperature. This is because bacteria that encounter such an environment A) undergo death by plasmolysis. B) are unable to metabolize the glucose or fructose, and thus starve to death. C) undergo death by lysis. D) are obligate anaerobes. E) are unable to swim through these thick and viscous materials
E
26.Which of the following series best reflects what we know about how the flu virus moves between species? A) An avian flu virus undergoes several mutations and rearrangements such that it is able to be transmitted to other birds and then to humans. B) The flu virus in a pig is mutated and replicated in alternate arrangements so that humans who eat the pig products can be infected. C) A flu virus from a human epidemic or pandemic infects birds; the birds replicate the virus differently and then pass it back to humans. D) An influenza virus gains new sequences of DNA from another virus, such as a herpesvirus; this enables it to be transmitted to a human host. E) An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates and is passed to a new species such as a bird, the virus mutates and can be transmitted to humans.
E
27.Which of the following is the most probable fate of a newly emerging virus that causes high mortality in its host? A) It is able to spread to a large number of new hosts quickly because the new hosts have no immunological memory of them. B) The new virus replicates quickly and undergoes rapid adaptation to a series of divergent hosts. C) A change in environmental conditions such as weather patterns quickly forces the new virus to invade new areas. D) Sporadic outbreaks will be followed almost immediately by a widespread pandemic. E) The newly emerging virus will die out rather quickly or will mutate to be far less lethal.
C
3.What is the function of reverse transcriptase in retroviruses? A)It converts host cell RNA into viral DNA. B)It hydrolyzes the host cellʹs DNA. C)It uses viral RNA as a template for DNA synthesis. D)It translates viral RNA into proteins. E)It uses viral RNA as a template for making complementary RNA strands.
photoautotroph, chemoautotroph, photoheterotroph, chemoheterotroph
4 major nutritional modes
D
4) The predatory bacterium, Bdellovibrio bacteriophorus, drills into a prey bacterium and, once inside, digests it. In an attack upon a gram-negative bacterium that has a slimy cell covering, what is the correct sequence of structures penetrated by B. bacteriophorus on its way to the prey's cytoplasm? 1. membrane composed mostly of lipopolysaccharide 2. membrane composed mostly of phospholipids 3. peptidoglycan 4. capsule A) 2, 4, 3, 1 B) 1, 3, 4, 2 C) 1, 4, 3, 2 D) 4, 1, 3, 2 E) 4, 3, 1, 2
A
4. Cyanobacteria are... A) photoautotrophs. B) photoheterotrophs. C) chemoautotrophs. D) chemoheterotrophs that perform decomposition. E) parasitic chemoheterotrophs.
C
5.Which of the following terms describes bacteriophage DNA that has become integrated into the host cell chromosome? A) intemperate bacteriophages B) transposons C) prophages D) provirus E) plasmids
A
6.Some pathogens undergo rapid changes resulting in antigenic variation. Which of the following is such a pathogen? A)the influenza virus, which expresses alternative envelope proteins B)the strep bacteria, which can be communicated from patient to patient with high efficiency C)human papilloma virus, that can remain latent for several years D)the causative agent of an autoimmune disease such as rheumatoid arthritis E)Chylamidias
Cells burst, The lytic cycle, an environmental signal that tells the virus to enter the lytic cycle
6.WHAT HAPPENS AT THE END OF THE LYSOGENIC CYCLE?
External environmental signal
7.WHAT CAUSES THE TRANSITION BETWEEN CYCLES?
D
A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have A) T2 protein and T4 DNA. B) T2 protein and T2 DNA. C) a mixture of the DNA and proteins of both phages. D) T4 protein and T4 DNA. E) T4 protein and T2 DNA
E
A fish that has been salt-cured subsequently develops a reddish color. You suspect that the fish has been contaminated by the extreme halophile, Halobacterium. Which of these features of cells removed from the surface of the fish, if confirmed, would support your suspicion? 1. the presence of the same photosynthetic pigments found in cyanobacteria 2. cell walls that lack peptidoglycan 3. cells that are isotonic to conditions on the surface of the fish 4. cells containing bacteriorhodopsin 5. the presence of very large numbers of ion pumps in its plasma membrane A) 2 and 5 B) 3 and 4 C) 1, 4, and 5 D) 3, 4, and 5 E) 2, 3, 4, and 5
C
A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. 54) Adherence to the intestinal lining by this bacterium is due to its possession of A) fimbriae. B) pili. C) a capsule. D) a flagellum. E) a cell wall with an outer lipopolysaccharide membrane.
C
A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. 55) What should be true of the cell wall of this bacterium? A) Its innermost layer is composed of a phospholipid bilayer. B) After it has been subjected to Gram staining, the cell should remain purple. C) It has an outer membrane of lipopolysaccharide. D) It is mostly composed of a complex, cross-linked polysaccharide. E) Two of the responses above are correct.
D
A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. 56) Some of the proteins that allow this bacterium to swim are related (in an evolutionary sense) to proteins that A) attach to the single chromosome. B) act as restriction enzymes. C) synthesize peptidoglycan for the cell wall. D) move penicillin out of the cell. E) comprise its ribosomes.
D
A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. 57) In which feature(s) should one be able to locate a complete chromosome of this bacterium? 1. nucleolus 2. prophage 3. endospore 4. nucleoid A) 4 only B) 1 and 3 C) 2 and 3 D) 3 and 4 E) 2, 3, and 4
C
A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. 58) The cell also lacks F factors and F plasmids. Upon its death, this bacterium should be able to participate in A) conjugation. B) transduction. C) transformation. D) Three of the responses above are correct. E) Two of the responses above are correct.
C
A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. 59) This bacterium derives nutrition by digesting human intestinal contents (in other words, food). Thus, this bacterium should be an A) aerobic chemoheterotroph. B) aerobic chemoautotroph. C) anaerobic chemoheterotroph. D) anaerobic chemoautotroph.
C
A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. 60) This bacterium derives nutrition by digesting human intestinal contents (in other words, food). Humans lacking this bacterium have no measurable reproductive advantage or disadvantage relative to humans who harbor this bacterium. Consequently, the bacterium can be properly described as which of the following? 1. symbiont 2. endosymbiont 3. mutualist 4. commensal A) 4 only B) 1 and 2 C) 1 and 4 D) 2 and 3 E) 2 and 4
C
A researcher lyses a cell that contains nucleic acid molecules and capsomeres of tobacco mosaic virus (TMV). The cell contents are left in a covered test tube overnight. The next day this mixture is sprayed on tobacco plants. Which of the following would be expected to occur? A) The plants would develop some but not all of the symptoms of the TMV infection. B) The plants would develop symptoms typically produced by viroids. C) The plants would develop the typical symptoms of TMV infection. D) The plants would not show any disease symptoms. E) The plants would become infected, but the sap from these plants would be unable to infect other plants.
A
Assuming that each of these possesses a cell wall, which prokaryotes should be expected to be most strongly resistant to plasmolysis in hypertonic environments? A) extreme halophiles B) extreme thermophiles C) methanogens D) cyanobacteria E) nitrogen-fixing bacteria that live in root nodules
B
Bacteria perform each of the following ecological roles. Which role typically does not involve a symbiosis? A) skin commensalist B) decomposer C) aggregates with methane-consuming archaea D) gut mutualist E) pathogen
E
Broad-spectrum antibiotics inhibit the growth of most intestinal bacteria. Consequently, assuming that nothing is done to counter the reduction of intestinal bacteria, a hospital patient who is receiving broad-spectrum antibiotics is most likely to become A) unable to fix carbon dioxide. B) antibiotic resistant. C) unable to fix nitrogen. D) unable to synthesize peptidoglycan. E) deficient in certain vitamins and nutrients.
D
Carl Woese and collaborators identified two major branches of prokaryotic evolution. What was the basis for dividing prokaryotes into two domains? A) microscopic examination of staining characteristics of the cell wall B) metabolic characteristics such as the production of methane gas C) metabolic characteristics such as chemoautotrophy and photosynthesis D) genetic characteristics such as ribosomal RNA sequences E) ecological characteristics such as the ability to survive in extreme environments
obligate anaerobe
DESCRIBES A CATEGORY OF LIFE THAT IS POISONED BY OXYGEN?
Host range
Each virus can infect cells of only a limited number of host species
D
Emerging viruses arise by A) mutation of existing viruses. B) the spread of existing viruses to new host species. C) the spread of existing viruses more widely within their host species. D) mutation of existing viruses, the spread of existing viruses to new host species, and the spread of existing viruses more widely within their host species. E) none of these.
B
Foods can be preserved in many ways by slowing or preventing bacterial growth. Which of these methods should be least effective at inhibiting bacterial growth? A) Refrigeration: slows bacterial metabolism and growth. B) Closing previously opened containers: prevents more bacteria from entering, and excludes O₂. C) Pickling: creates a pH at which most bacterial enzymes cannot function. D) Canning in heavy sugar syrup: creates osmotic conditions that remove water from most bacterial cells. E) Irradiation: kills bacteria by mutating their DNA to such an extent that their DNA-repair enzymes are overwhelmed.
E. coli
GIVE ME A BACTERIAL EXAMPLE OF COMMENSALSIM
Chlamydia, Rickettsia
GIVE ME A EXAMPLE OF AN OBGLIGATE INTRACELLULAR BACTERIA
E
Genetic variation in bacterial populations cannot result from A) transduction. B) transformation C) conjugation D) mutation. E) meiosis.
viral envelopes function
Help infect the host
A
Hershey and Chase performed an elegant experiment that convinced most biologists that DNA, rather than protein, was the genetic material. This experiment subjected bacteria to the same gene transfer mechanism as occurs in A) transduction. B) transformation. C) conjugation. D) binary fission. E) endosymbiosis.
A
If a bacterium regenerates from an endospore that did not possess any of the plasmids that were contained in its original parent cell, the regenerated bacterium will probably also A) lack antibiotic-resistant genes. B) lack a cell wall. C) lack a chromosome. D) lack water in its cytoplasm. E) be unable to survive in its normal environment.
D
If all prokaryotes on Earth suddenly vanished, which of the following would be the most likely and most direct result? A) The number of organisms on Earth would decrease by 1020%. B) Human populations would thrive in the absence of disease. C) Bacteriophage numbers would dramatically increase. D) The recycling of nutrients would be greatly reduced, at least initially. E) There would be no more pathogens on Earth.
D
If archaeans are more closely related to eukaryotes than to bacteria, then which of the following is a reasonable prediction? A) Archaean DNA should have no introns. B) Archaean chromosomes should have no protein bonded to them. C) Archaean DNA should be single-stranded. D) Archaean ribosomes should be larger than typical prokaryotic ribosomes. E) Archaeans should lack cell walls.
E
In Fred Griffith's experiments, harmless R strain pneumococcus became lethal S strain pneumococcus as the result of which of the following? 1. horizontal gene transfer 2. transduction 3. conjugation 4. transformation 5. genetic recombination A) 2 only B) 4 only C) 2 and 5 D) 1, 3, and 5 E) 1, 4, and 5
C
In a hypothetical situation, a bacterium lives on the surface of a leaf, where it obtains nutrition from the leaf's nonliving, waxy covering while inhibiting the growth of other microbes that are plant pathogens. If this bacterium gains access to the inside of a leaf, however, it causes a fatal disease in the plant. Once the plant dies, the bacterium and its offspring decompose the plant. What is the correct sequence of ecological roles played by the bacterium in the situation described here? Use only those that apply. 1. nutrient recycler 2. mutualist 3. commensal 4.parasite 5. primary producer A) 1, 3, 4 B) 2, 3, 4 C) 2, 4, 1 D) 1, 2, 5 E) 1, 2, 3
B
In a hypothetical situation, the genes for sex pilus construction and for tetracycline resistance are located together on the same plasmid within a particular bacterium. If this bacterium readily performs conjugation involving a copy of this plasmid, then the result should be A) a bacterium that has undergone transduction. B) the rapid spread of tetracycline resistance to other bacteria in that habitat. C) the subsequent loss of tetracycline resistance from this bacterium. D) the production of endospores among the bacterium's progeny. E) the temporary possession by this bacterium of a completely diploid genome
B
In general, what is the primary ecological role of prokaryotes? A) parasitizing eukaryotes, thus causing diseases B) breaking down organic matter C) metabolizing materials in extreme environments D) adding methane to the atmosphere E) serving as primary producers in terrestrial environments
C
In many ways, the regulation of the genes of a particular group of viruses will be similar to the regulation of the host genes. Therefore, which of the following would you expect of the genes of the bacteriophage? A) regulation via acetylation of histones B) positive control mechanisms rather than negative C) control of more than one gene in an operon D) reliance on transcription activators E) utilization of eukaryotic polymerases
Archaea
Live in environments so extreme that few other organisms survive there
D
Match the numbered terms to the description that follows. Choose all appropriate terms. 1. autotroph 2. heterotroph 3. phototroph 4. chemotroph a prokaryote that obtains both energy and carbon as it decomposes dead organisms A) 1 only B) 4 only C) 1 and 3 D) 2 and 4 E) 1, 3, and 4
D
Match the numbered terms to the description that follows. Choose all appropriate terms. 1. autotroph 2. heterotroph 3. phototroph 4. chemotroph an organism that obtains both carbon and energy by ingesting prey A) 1 only B) 4 only C) 1 and 3 D) 2 and 4 E) 1, 3, and 4
B
Match the numbered terms to the description that follows. Choose all appropriate terms. 1. autotroph 2. heterotroph 3. phototroph 4. chemotroph an organism that relies on photons to excite electrons within its membranes A) 1 only B) 3 only C) 1 and 3 D) 2 and 4 E) 1, 3, and 4
E
Most molecular biologists think that viruses originated from fragments of cellular nucleic acid. Which of the following observations supports this theory? A) Viruses contain either DNA or RNA. B) Viruses are enclosed in protein capsids rather than plasma membranes. C) Viruses can reproduce only inside host cells. D) Viruses can infect both prokaryotic and eukaryotic cells. E) Viral genomes are usually similar to the genome of the host cell.
E
Nitrogenase, the enzyme that catalyzes nitrogen fixation, is inhibited whenever free O₂ reaches a critical concentration. Consequently, nitrogen fixation cannot occur in cells wherein photosynthesis produces free O₂. Consider the colonial aquatic cyanobacterium, Anabaena, whose heterocytes are described as having "...a thickened cell wall that restricts entry of O₂ produced by neighboring cells. Intracellular connections allow heterocysts to transport fixed nitrogen to neighboring cells in exchange for carbohydrates." 61) Given that the enzymes that catalyze nitrogen fixation are inhibited by oxygen, what are two "strategies" that nitrogen-fixing prokaryotes might use to protect these enzymes from oxygen? 1. couple them with photosystem II (the photosystem that splits water molecules) 2. package them in membranes that are impermeable to all gases 3. be obligate anaerobes 4. be strict aerobes 5. package these enzymes in specialized cells or compartments that inhibit oxygen entry A) 1 and 4 B) 2 and 4 C) 2 and 5 D) 3 and 4 E) 3 and 5
B
Nitrogenase, the enzyme that catalyzes nitrogen fixation, is inhibited whenever free O₂ reaches a critical concentration. Consequently, nitrogen fixation cannot occur in cells wherein photosynthesis produces free O₂. Consider the colonial aquatic cyanobacterium, Anabaena, whose heterocytes are described as having "...a thickened cell wall that restricts entry of O₂ produced by neighboring cells. Intracellular connections allow heterocysts to transport fixed nitrogen to neighboring cells in exchange for carbohydrates." 62) Which two questions below arise from a careful reading of this quotation, and are most important for understanding how N₂ enters heterocysts, and how O₂ is kept out of heterocysts? 1. If carbohydrates can enter the heterocysts from neighboring cells via the "intracellular connections," how is it that O₂ doesn't also enter via this route? 2. If the cell walls of Anabaena's photosynthetic cells are permeable to O₂ and CO₂, are they also permeable to N₂? 3. If the nuclei of the photosynthetic cells contain the genes that code for nitrogen fixation, how can these cells fail to perform nitrogen fixation? 4. If the nuclei of the heterocysts contain the genes that code for photosynthesis, how can these cells fail to perform photosynthesis? 5. If the cell walls of Anabaena's heterocysts are permeable to N₂, how is it that N₂ doesn't diffuse out of the heterocysts before it can be fixed? 6. If the thick cell walls of the heterocysts exclude entry of oxygen gas, how is it that they don't also exclude the entry of nitrogen gas? A) 1 and 3 B) 1 and 6 C) 2 and 5 D) 3 and 4 E) 4 and 6
A
Photoautotrophs use A) light as an energy source and CO₂ as a carbon source. B) light as an energy source and methane as a carbon source. C) N₂ as an energy source and CO₂ as a carbon source. D) CO₂ as both an energy source and a carbon source. E) H₂S as an energy source and CO₂ as a carbon source.
A
Plantlike photosynthesis that releases O₂ occurs in A) cyanobacteria. B) chlamydias. C) archaea. D) actinomycetes. E) chemoautotrophic bacteria.
D
Regarding prokaryotic genetics, which statement is correct? A) Crossing over during prophase I introduces some genetic variation. B) Prokaryotes feature the union of haploid gametes, as do eukaryotes. C) Prokaryotes exchange some of their genes by conjugation, the union of haploid gametes, and transduction. D) Mutation is a primary source of variation in prokaryote populations. E) Prokaryotes skip sexual life cycles because their life cycle is too short.
Attatchment
The T4 phage uses its tail fibers to bind to specific receptor sites on the outer surface of an E. coli cell
Synthesis of Viral genomes and proteins.
The phage DNA directs production of phage proteins and copies of the phage genome by host and viral enzymes, using components within the cell.
Release
The phage directs production of an enzyme that damages the bacterial cell wall, allowing fluid to enter. The cell swells and finally bursts, releasing 100 to 200 phage particles.
Entry of phage DNA and degradation of host DNA.
The sheath of the tail contracts, injecting the phage DNA into the cell and leaving an empty capsid outside. The cell's DNA is hydrolyzed.
D
The termite gut protist, Mixotricha paradoxa, has at least two kinds of bacteria attached to its outer surface. One kind is a spirochete that propels its host through the termite gut. A second type of bacteria synthesizes ATP, some of which is used by the spirochetes. The locomotion provided by the spirochetes introduces the ATP-producing bacteria to new food sources. Which term(s) is (are) applicable to the relationship between the two kinds of bacteria? 1. mutualism 2. parasitism 3. symbiosis 4. metabolic cooperation A) 1 only B) 1 and 2 C) 2 and 3 D) 1, 3, and 4 E) 2, 3, and 4
C
The thermoacidophile, Sulfolobus acidocaldarius, lacks peptidoglycan, but still possesses a cell wall. What is likely to be true of this species? 1. It is a bacterium. 2. It is an archaean. 3. The optimal pH of its enzymes will lie above pH 4. The optimal pH of its enzymes will lie below pH 5. It could inhabit certain hydrothermal springs. 6. It could inhabit alkaline hot springs. A) 1, 3, and 6 B) 2, 4, and 6 C) 2, 4, and 5 D) 1, 3, and 5 E) 1, 4, and 5
C
The typical prokaryotic flagellum features A) an internal 9 + 2 pattern of microtubules. B) an external covering provided by the plasma membrane. C) a complex "motor" embedded in the cell wall and plasma membrane. D) a basal body that is similar in structure to the cell's centrioles. E) a membrane-enclosed organelle with motor proteins.
Assembly
Three separate sets of proteins self-assemble to form phage heads, tails, and tail fibers. The phage genome is packaged inside the capsid as the head forms.
C
To cause a human pandemic, the H5N1 avian flu virus would have to A) spread to primates such as chimpanzees. B) develop into a virus with a different host range. C) become capable of human-to-human transmission. D) arise independently in chickens in North and South America. E) become much more pathogenic.
B
Viral envelopes can best be analyzed with which of the following techniques? A) transmission electron microscopy B) antibodies against specific proteins not found in the host membranes C) staining and visualization with the light microscope D) use of plaque assays for quantitative measurement of viral titer E) immunofluorescent tagging of capsid proteins
Double or single stranded RNA (RNA virus) or Double or single stranded DNA (DNA virus)
Viral genomes may consist of either
D
Viral genomes vary greatly in size and may include from four genes to several hundred genes. Which of the following viral features is most apt to correlate with the size of the genome? A) size of the viral capsomeres B) RNA versus DNA genome C) double- versus single-strand genomes D) size and shape of the capsid E) glycoproteins of the envelope
D
Which of the following accounts for someone who has had a herpesvirus-mediated cold sore or genital sore getting flare-ups for the rest of his or her life? A) re-infection by a closely related herpesvirus of a different strain B) re-infection by the same herpesvirus strain C) co-infection with an unrelated virus that causes the same symptoms D) copies of the herpesvirus genome permanently maintained in host nuclei E) copies of the herpesvirus genome permanently maintained in host cell cytoplasm
D
Which of the following involves metabolic cooperation among prokaryotic cells? A) binary fission B) endospore formation C) endotoxin release D) biofilms E) photoautotrophy
D
Which of the following is an important source of endotoxin in gram-negative species? A) endospore B) sex pilus C) flagellum D) cell wall E) capsule
D
Which of the following is characteristic of the lytic cycle? A) Many bacterial cells containing viral DNA are produced. B) Viral DNA is incorporated into the host genome. C) The viral genome replicates without destroying the host. D) A large number of phages are released at a time. E) The virus-host relationship usually lasts for generations.
E
Which of the following is least associated with the others? A) horizontal gene transfer B) genetic recombination C) conjugation D) transformation E) binary fission
A
Which of the following is the best predictor of how much damage a virus causes? A) ability of the infected cell to undergo normal cell division B) ability of the infected cell to carry on translation C) whether the infected cell produces viral protein D) whether the viral mRNA can be transcribed E) how much toxin the virus produces
C
Which of the following obtain energy by oxidizing inorganic substancesenergy that is used, in part, to fix CO₂? A) photoautotrophs B) photoheterotrophs C) chemoautotrophs D) chemoheterotrophs that perform decomposition E) parasitic chemoheterotrophs
D
Which of the following statements is not true? A) Archaea and bacteria have different membrane lipids. B) Both archaea and bacteria generally lack membrane-enclosed organelles. C) The cell walls of archaea lack peptidoglycan. D) Only bacteria have histones associated with DNA. E) Only some archaea use CO₂ to oxidize H₂, releasing methane.
D
Which of the following traits do archaeans and bacteria share? 1. composition of the cell wall 2. presence of plasma membrane 3. lack of a nuclear envelope 4. identical rRNA sequences A) 1 only B) 3 only C) 1 and 3 D) 2 and 3 E) 2 and 4
F plasmid
allows cells to function as DNA donors during conjugation
Rhizobium
alpha proteobacteria that live in nodules within the roots of legumes where the bacteria converts N2 to compounds the host plant can use to make proteins
parasitism
an organism called a parasite harms but does not kill its host
endotoxins
are released only when bacteria die and their cell walls break down
exotoxins
are secreted and cause disease even if the prokaryotes that produce them are not present
Rapid reproduction
binary fission allows organisms to rapidly evolve
mutualism
both symbiotic organisms benefit
extremophiles
organism that favor extreme environments
horizontal gene transfer
movement of genes from one organism to another
Icosahedral viruses
multiple identical protein molecules arranged in a polyhedral capsid with 20 triangular facets (icosahedron)
obligate aerobes
must use O2 for cellular respiration and cannot grow without it
commensalism
one organism benefits while neither harming nor helping the other in any significant way
capsomeres
protein subunits that make up capsids
main defense against phages
restrictions are the
HIV
retrovirus that causes AIDS
anaerobic respiration
substances other than O2, like Nitrate ions (NO3-) or sulfate ions accept electrons at the downhill end of the electron transport chain
Viral envelope strucutre
surround the capsids of influenza viruses and many other viruses found in animals
taxis
the ability to move toward or away from a stimulus
conjugation
the process where genetic material is transferred between prokaryotic cells
capsid
the protein shell that encloses a viral genome
facultative anaerobes
use O2 if it is present but can also carry out fermentation or anaerobic respiration in an anaerobic environment
retovirus
uses reverse transcriptase to copy their RNA genome into DNA
horizontal transmission
virus entering through damaged cell walls due to wind, injury, or herbivores
Nitrogen fixation
— some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3) and cells incorporate the fixed nitrogen into amino acids and other organic molecules •Increases the nitrogen available to plants who can't use atmospheric nitrogen
Why is viral life not considered alive?
• Biologically inert • unable to reproduce outside of host cell • can't regenerate ATP (metabolic processes)
Bacteriophages
• a virus that infects bacteria • have the most complex capsids found among viruses • phages T1-T7 infect E. coli and were the first studied • Three even phages (T2, T4, T6) are similar in structure and have elongated icosahedral heads enclosing their DNA . A protein tail piece attaches the phage to the host and injects the phage DNA inside
cell surface structures
•An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, protects the cell, and prevents it from bursting in a hypotonic environment •Bacterial cell walls contain peptidoglycan •Archaea contain polysaccharides and proteins but lack peptidoglycan •Many antibiotics target peptidoglycan and damage bacterial cell walls •Capsules and slime walls can protect against dehydration and host immune systems; enables prokaryotes to adhere to their substrate or to other individuals in a colony •Peptidoglycan: a polymer composed of modified sugar cross-linked by short polypeptides; encloses the entire bacterium and anchors other molecules that extend from its surface •Capsule: dense and well-defined polysaccharide or protein layer that covers many prokaryotes •Slime wall •Fimbriae •Pili (sex pili)
E. coli
•Can divide every 20 minutes under ideal lab conditions but only 12-24 hours in its natural environment •Model organism in research which has led to important advances in DNA technology •Gamma proteobacteria •Example of commensalism •Harmless symbiont in human intestines but horizontal gene transfer can cause it to become pathogenic
short generation ramifications
•Cells eventually exhaust their nutrient supply, poison themselves with metabolic wastes, face competition from other microorganisms, or are consumed by other organisms •Can substantially evolve in short periods of time •Prokaryotes can adapt rapidly to new conditions
Viral disease in plants
•More than 2,000 viruses cause spots on leaves and fruits, stunted growth, and damaged flowers or roots •Most plant viruses have an RNA genome •Plant viruses spread disease in two major modes oHorizontal transmission oVertical transmission
antibiotic resistance
•Mutations in chromosomal genes of a pathogen cause resistance because it is less likely that the pathogen will transfer a certain antibiotic into the cell •Altered intracellular target protein for an antibiotic molecule reduces its inhibitory effect
Nitrogen Metabolism
•Nitrogen is essential for the production of amino acids and nucleic acids •Prokaryotes can metabolize nitrogen in a variety of ways
simple viral cycle
•Once a viral genome has entered a cell, the cell begins to manufacture viral proteins •The virus makes use of host enzymes, ribosomes, tRNAs, amino acids, ATP, and other molecules •Viral nucleic acid molecules and capsomeres spontaneously self-assemble into new viruses •The simplest cycle ends with the exit of hundreds or thousands of viruses from the infected host cell which will damage or destroy the cell •Two main cycles are lytic and lysogenic
prokaryotic DNA
•Prokaryotes lack a membrane bounded nucleus -nucleiod -plasmid
bacteria internal organization
•Prokaryotic cells usually lack complex compartmentalization •Some prokaryotes do have specialized membranes that perform metabolic functions. These membranes are usually infoldings of the plasma membrane •Prokaryotic genome has less DNA than eukaryotes •Genome consists of a circular chromosome with many fewer proteins found in the linear chromosome of eukaryotes •DNA replication, transcription, and translation is similar to that of a eukaryote however prokaryotic ribosomes are smaller & differ in protein & RNA content which allows certain antibiotics, such as erythromycin and tetracycline, to bnd to ribosomes and block protein synthesis
genetic recombination
•The combining of DNA from two sources •Transformation, transduction, and conjugation bring prokaryotic DNA from different cells together
Evolution of viruses
•Viruses are found in every form of life (archaea, fungi, protists, plants, animals, bacteria) •Viruses do not fit our definition of living organisms •Since viruses can replicate only within cells, they probably evolved as bits of cellular nucleic acid •Candidates for the source of viral genomes are plasmids, circular DNA in bacteria and yeasts, and transposons, small mobile DNA segments •Plasmids, transposons, and viruses are all mobile genetic elements •Mimivirus, a double-stranded DNA virus, the largest virus yet discovered, is the size of a small bacterium •There is controversy about whether this virus evolved before or after cells
spontaneous assembly of viruses
•Viruses are obligate intracellular parasites, which means they can replicate only within a host cell •Each virus has a host range, a limited number oh host cells it can infect •Once a viral genome has entered a cell, the cell begins to manufacture viral proteins •The virus makes use of host enzymes, ribosomes, tRNAs, amino acids, ATP, and other molecules •Viral nucleic acid molecules and capsomeres spontaneously self-assemble into new viruses
viruses jumping hosts (species)
•Viruses mutate as they pass from one host species to another. When an animal like a pig or a bird is infected with more than one strain of flu virus, the different strains can undergo genetic recombination if the RNA molecules making up the genomes mix and match during viral assembly •Pigs are thought to have been the breeding ground for the 2009 flu virus, which contained sequences from bird, pig, and human flu viruses
Vaccines
•a harmless variant or derivative of a pathogen that stimulates a host's immune system to mount defenses against the pathogen •can prevent certain viral illnesses such as small-pox, rubella, mumps, hepatitis B, influenza, polio, measles
lytic cycle
•a phage replicative cycle that culminates in the death of the host cell; •produces new phages and lyses (breaks open) the host's cell wall, releasing the progeny viruses •a phage that only reproduces by the lytic cycle is called a virulent phage •Bacteria have defenses against phages, including restriction enzymes that recognize and cut up certain phages
peptidoglycans
•a polymer composed of modified sugar cross-linked by short polypeptides •encloses the entire bacterium and anchors other molecules that extend from its surface •cells with high amounts can be attacked by antibiotics
lysogenic cycle
•a type of phage replicative cycle in which the viral genome becomes incorporated into the bacterial host chromosome as a prophage, is replicated along with the chromosome, and does not kill the host •Every time the host divides, it copies the phage DNA and passes the copies to daughter cells •An environmental signal can trigger the virus genome to exit the bacterial chromosome and switch to the lytic mode