Ch 18 Viruses and Bacteria 04 Biology 2008 From Mrs. C. Phillips, DHS black Ch 18.1 Viruses • What kinds of diseases are caused by viruses? • Measles • Mumps • Rubella • Chicken pox • Polio • Cold sores • Herpes • Rabies • Flu • Cold • HIV • Viral pneumonia • Hepatitis • Mono (if caused by Epstein-Barr virus) What kingdom do viruses belong to? • None- they are not alive!! • They are nonliving particles that cause disease • pathogens: agents that cause disease • Characteristics: – 1/2 -1/100 the size of the smallest bacteria – Do not grow, respire, metabolize, develop, respire, maintain homeostasis – Do not have scientific names (named for the disease or tissue they infect) • Ex: adenovirus (cold virus) infects adenoid tissue Viral Structure 1 Viral Structure • A virus has an inner Capsid core of nucleic acid, either RNA or DNA, and an outer Nucleic protein coat called acid a capsid. Envelope • Some relatively large viruses may have an additional layer, called an envelope, surrounding their capsids. • The arrangement of Capsid proteins in the capsid Nucleic acid of a virus determines the virus’s shape. • Polyhedral viruses resemble small crystals. Nucleic acid • The tobacco mosaic virus has a long, narrow helical shape. Capsid Replication of Viruses • There are two ways in which a virus can repilcate: 1. Lytic Cycle and 2. Lysogenic Cycle Each cycle first involves attachment to the host cell. Attachment • A virus recognizes and attaches to a host cell when one of its proteins interlocks with a molecular shape that is the receptor site on the host cell’s plasma membrane. • Viruses are specific to only certain types of cells. Host specificity Capsid • The T4 bacteriophage Nucleic can only infect E. Coli acid cells. • HIV can only infect Tail certain white blood cells. Tail fiber • Polio can only infect intestinal and nerve cells. Lytic Cycle Bacteriophage Bacterial DNA Nucleic acid Bacterial host cell B. Entry A. Attachment The bacteriophage injects its nucleic acid into the bacterial cell. E. Lysis and Release The host cell breaks open and releases new virus particles. C. Replication D. Assembly The host’s metabolic New virus particles machinery makes viral are assembled. nucleic acid and proteins. Lytic Cycle Lysogenic Cycle B. Provirus Formation A. Attachment and Entry Provirus Although the provirus is inactive, Bacterial host C. Cell Division it replicates along with chromosome the host cell’s chromosome. A lysogenic virus The viral nucleic acid is called injects its nucleic a provirus when it becomes acid into a bacterium. part of the host’s chromosome. LYSOGENIC CYCLE LYTIC CYCLE The provirus leaves the chromosome. The cell breaks open releasing viruses. Viral nucleic acid and proteins are made. Lysogenic Cycle Release of Viruses • Either lysis, the bursting of a cell, or exocytosis, the active transport process by which materials are expelled from a cell, release new viruses from the host cell. Retroviruses • Have RNA as their nucleic acid • Once inside cell, the RNA is turned into DNA by a process called reverse transcription HIV virus Reverse Transciption • This requires the enzyme reverse transcriptase which is carried along in the virus. • Then the viral DNA becomes part of the host’s DNA as a provirus. Retrovirus Cycle Retrovirus RNA DNA is made from RNA the viral RNA. DNA Reverse transcriptase Entering cell Provirus in host chromosome mRNA Retrovirus Cycle New virus parts Exiting New virus cell forming Question 1 Which of the following is NOT a reason that viruses are considered to be nonliving? A. Viruses don’t replicate. B. Viruses don’t respire. C. Viruses don’t grow. D. Viruses don’t develop. The answer is A. Question 2 Which is NOT a component of a virus? A. RNA B. capsid C. DNA D. phage The answer is D. Question 3 Which of the following is NOT determined by the arrangement of proteins in the capsid of a virus? A. shape B. what cell can be infected by the virus C. whether or not the virus will have an envelope around it D. how the virus infects a cell The answer is C. Question 4 What two ways do viruses have of getting into host cells? Answer The virus can inject its nucleic acid into the host cell, or attach to the host cell’s membrane and become surrounded by the membrane and placed in a vacuole. The virus then bursts out of the vacuole and releases its nucleic acid into the cell. Question 5 In the lytic cycle, after the host’s metabolic machinery makes viral nucleic acid and proteins the next phase is _______. A. lysis and release B. replication C. assembly D. attachment The answer is C. In the assembly phase, the new virus particles are assembled. Ch 18.2 Bacteria • Bacteria • Bacteria Importance • Bacteria Diseases • Bacterial Reproduction Question 6 Which of the following is not a way to identify bacteria? A. the way in which their cell walls reflect Gram stain B. shape C. characteristic growth patterns D. lack of a plasma membrane The answer is D. Question 7 Given their rapid reproductive rates, why aren’t there more bacteria than there actually are? Answer Bacteria don’t always have ideal growing conditions. They run out of nutrients and water, they poison themselves with their own wastes, and predators eat them. Question 8 What is a pilus used for in a bacterium? A pilus helps a bacterium stick to a surface. It is also a bridge through or on which two bacteria can exchange DNA. Capsule Cell Wall Chromosome Plasma Flagellum membrane Pilus Plasmid Question 9 With lysogenic viruses, what two phases of the lytic cycle are replaced by the lysogenic cycle? A. entry and replication B. replication and assemble C. assembly and lysis and release D. attachment and entry The answer is D. A. Attachment and Entry LYSOGENIC CYCLE LYTIC CYCLE Question 10 Explain why you can be infected with a virus but may have no symptoms of disease for years after the initial infection. Answer The virus enters a lysogenic phase remaining inactive but replicating along with the host cell’s chromosomes. Eventually, the virus enters a lytic phase where it destroys its host cells and causes symptoms of disease. Question 11 What is the difference between lysis and exocytosis with respect to host cells that contain viruses? Answer Lysis, the bursting of the host cell, is caused when viruses break out of it. In exocytosis, the virus is enclosed in a vacuole that then fuses with the host cell’s plasma membrane. The virus is then released to the outside. Question 12 What is the importance of reverse transcriptase to a retrovirus? Answer The enzyme reverse transcriptase allows the retrovirus to make DNA from its RNA so the DNA may attach to the chromosomes of the host cell and divide with the host cell. Question 13 Particles that are composed of proteins but have no nucleic acid to carry genetic information are _______. A. proviruses B. prions C. viroids D. retroviruses The answer is B. Question 14 During ______, a bacterium transfers all or part of its chromosome to another bacterium. A. binary fission B. attachment C. conjugation D. chemosynthesis The answer is C. Question 15 What causes botulism? Answer Endospores of C. botulinum bacteria get into an anaerobic environment like improperly canned food, germinate, and produce a toxin as they grow. This toxin is then ingested by humans and causes poisoning called botulism. Question 16 What causes anthrax? Endospores of B. anthracis bacteria produce endospores that can become airborne, and if inhaled in large amounts, can germinate in a person’s lungs causing a deadly infection that damages lung tissue and the circulatory system. Question 17 Describe the process in which bacteria make nitrogen in the air accessible for use by plants. Answer Several species of bacteria have enzymes that convert nitrogen gas into ammonia. Other bacteria then convert the ammonia into nitrite and nitrate that plants can use. Question 18 What are the two ways in which bacterial diseases harm people? Answer The growth of the bacteria can interfere with the normal function of body tissue, or the bacteria can release a toxin that directly attacks the host.
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