Microbiology Unit Outline Name ______Chapter 10: the Genetics of Viruses and Bacteria 10.17 Viral DNA May Become Part of the Host Chromosome 1
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Microbiology Unit Outline Name _______________________ Chapter 10: The Genetics of Viruses and Bacteria 10.17 Viral DNA may become part of the host chromosome 1. A virus is essentially “genes in a box,” an infectious particle consisting of a bit of nucleic acid, wrapped in a protein coat called a capsid, and in some cases, a membrane envelope. 2. Viruses have two types of reproductive cycles. a. In the lytic cycle viral particles are produced using host cell components, the host cell lyses, and viruses are released. b. Lysogenic cycle i. Viral DNA is inserted into the host chromosome by recombination. ii. Viral DNA is duplicated along with the host chromosome during each cell division. iii. The inserted phage DNA is called a prophage. Most prophage genes are inactive. iv. Environmental signals can cause a switch to the lytic cycle, causing the viral DNA to be excised from the bacterial chromosome and leading to the death of the host cell. 10.18 Many viruses cause disease in animals and plants 1. Viruses can cause disease in animals and plants. 2. DNA viruses and RNA viruses cause disease in animals. 3. A typical animal virus has a membranous outer envelope and projecting spikes of glycoprotein. 4. The envelope helps the virus enter and leave the host cell. 5. Many animal viruses have RNA rather than DNA as their genetic material. These include viruses that cause the common cold, measles, mumps, polio, and AIDS. 6. The reproductive cycle of the mumps virus, a typical enveloped RNA virus, has seven major steps: a. entry of the protein-coated RNA into the cell b. uncoating—the removal of the protein coat c. RNA synthesis—mRNA synthesis using a viral enzyme d. protein synthesis—mRNA is used to make viral proteins e. new viral genome production—mRNA is used as a template to synthesize new viral genomes f. assembly—the new coat proteins assemble around the new viral RNA 1 g. exit—the viruses leave the cell by cloaking themselves in the host cell’s plasma membrane. 7. Some animal viruses, such as herpes viruses, reproduce in the cell nucleus. 8. Most plant viruses are RNA viruses. a. To infect a plant, they must get past the outer protective layer of the plant. b. Viruses spread from cell to cell through plasmodesmata. c. Infection can spread to other plants by insects, herbivores, humans, or farming tools. 9. There are no cures for most viral diseases of plants or animals. 10.19 Emerging viruses threaten human health 1. Viruses that appear suddenly or are new to medical scientists are called emerging viruses. These include the AIDS virus, Ebola virus, West Nile virus, and SARS virus. 2. Three processes contribute to the emergence of viral diseases: a. mutation—RNA viruses mutate rapidly. b. contact between species—viruses from other animals spread to humans. c. spread from isolated human populations to larger human populations, often over great distances. 10.20 The AIDS virus makes DNA on an RNA template 1. AIDS (acquired immunodeficiency syndrome) is caused by HIV (human immunodeficiency virus). 2. HIV a. is an RNA virus, has two copies of its RNA genome, b. carries molecules of reverse transcriptase, which causes reverse transcription, producing DNA from an RNA template. 2 3. After HIV RNA is uncoated in the cytoplasm of the host cell, a. reverse transcriptase makes one DNA strand from RNA, reverse transcriptase adds a complementary DNA strand b. double-stranded viral DNA enters the nucleus and integrates into the chromosome, becoming a provirus, the provirus DNA is used to produce more mRNA copies c. the viral mRNA is translated to produce viral proteins, and new viral particles are assembled, leave the host cell, and can then infect other cells. 10.21 Viroids and prions are formidable pathogens in plants and animals 1. Some infectious agents are made only of RNA or protein. a. Viroids are small, circular RNA molecules that infect plants. Viroids replicate within host cells without producing proteins and interfere with plant growth. b. Prions are infectious proteins that cause degenerative brain diseases in animals. Prions- appear to be misfolded forms of normal brain proteins & which convert normal protein to misfolded form. Viruses Prions Infectious agents that is made up of a nucleic Infectious protein particle. acid in a protein coat. Simple particle that is able to multiply only Less complex than a virus. Body cell proteins within the living cells of a host misfold when prion is present. Can cause a wide variety of infections Mainly causes neuro-degenerative diseases 10.22 Bacteria can transfer DNA in three ways 1. Viral reproduction allows researchers to learn more about the mechanisms that regulate DNA replication and gene expression in living cells. 2. Bacteria are also valuable but for different reasons. a. Bacterial DNA is found in a single, closed loop chromosome. b. Bacterial cells divide by replication of the bacterial chromosome and then by binary fission. c. Because binary fission is an asexual process, bacteria in a colony are genetically identical to the parent cell. 3. Bacteria use three mechanisms to move genes from cell to cell. 4. Once new DNA gets into a bacterial cell, part of it may then integrate into the recipient’s chromosome. 3 a. Transformation is the b. Transduction is gene transfer c. Conjugation is the transfer of uptake of DNA from the by phages. DNA from a donor to a recipient surrounding environment. bacterial cell through a cytoplasmic (mating) bridge. 10.23 Bacterial plasmids can serve as carriers for gene transfer 1. The ability of a donor E. coli cell to carry out conjugation is usually due to a specific piece of DNA called the F factor. 2. During conjugation, the F factor is integrated into the bacterium’s chromosome. 3. The donor chromosome starts replicating at the F factor’s origin of replication. 4. The growing copy of the DNA peels off and heads into the recipient cell. 5. The F factor serves as the leading end of the transferred DNA. 6. An F factor can also exist as a plasmid, a small circular DNA molecule separate from the bacterial chromosome. a. Some plasmids, including the F factor, can bring about conjugation and move to another cell in linear form. b. The transferred plasmid re-forms a circle in the recipient cell. Chapter 16: Prokaryotes Introduction A. The abundant life of a coral reef depends upon microbes. 1. Photosynthesis by protists and prokaryotes feed all of the animals. 2. Prokaryotes convert dead organic material into fertilizer. 3. Protists that reside in the cells of corals use photosynthesis to produce sugars that nourish their hosts. B. Prokaryotes and protists are essential to the health of every ecosystem, including the human body. Prokaryotes 16.1 Prokaryotes are diverse and widespread 1. Prokaryotic cells are smaller than eukaryotic cells. a. Prokaryotes range from 1–5 µm in diameter. b. Eukaryotes range from 10–100 µm in diameter. 2. The collective biomass of prokaryotes is at least 10 times that of all eukaryotes. 3. Prokaryotes live in habitats too cold, too hot, too salty, too acidic, and too alkaline for eukaryotes to survive. 4. Some bacteria are pathogens, causing disease. But most bacteria on our bodies are benign or beneficial. 5. Several hundred species of bacteria live in and on our bodies a. decomposing dead skin cells b. supplying essential vitamins c. guarding against pathogenic organisms 6. Prokaryotes in soil decompose dead organisms, sustaining chemical cycles. 4 16.2 External features contribute to the success of prokaryotes 1. Prokaryotic cells have three common cell shapes. a. Cocci are spherical prokaryotic cells. They sometimes occur in chains that are called streptococci. b. Bacilli are rod-shaped prokaryotes. Bacilli may also be threadlike, or filamentous. c. Spiral prokaryotes are like a corkscrew. i. Short and rigid prokaryotes are called spirilla. ii. Longer, more flexible cells are called spirochetes. 2. Nearly all prokaryotes have a cell wall. Cell walls provide physical protection and prevent the cell from bursting in a hypotonic environment. 3. When stained with Gram stain, cell walls of bacteria are either a. Gram-positive, with simpler cell walls containing peptidoglycan b. Gram-negative, with less peptidoglycan and are more complex and more likely to cause disease. 4. The cell wall of many prokaryotes is covered by a capsule, a sticky layer of polysaccharides or protein. 5. The capsule a. enables prokaryotes to adhere to their substrate or to other individuals in a colony b. shields pathogenic prokaryotes from attacks by a host’s immune system. 6. Some prokaryotes have external structures that extend beyond the cell wall. a. Flagella help prokaryotes move in their environment. b. Hairlike projections called fimbriae enable prokaryotes to stick to their substrate or each other. 5 16.3 Populations of prokaryotes can adapt rapidly to changes in the environment 1. Prokaryote population growth a. occurs by binary fission & can rapidly produce a new generation within hours b. can generate a great deal of genetic variation by spontaneous mutations increasing the likelihood that some members of the population will survive changes in the environment. 2. The genome of a prokaryote typically a. has about one-thousandth as much DNA as a eukaryotic genome b. is one long, circular chromosome packed into a distinct region of the cell. 3. Many prokaryotes also have additional small, circular DNA molecules called plasmids, which replicate independently of the chromosome. 4. Some prokaryotes form specialized cells called endospores that remain dormant through harsh conditions. 5. Endospores can survive extreme heat or cold. 16.4 Prokaryotes have unparalleled nutritional diversity 1.