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Viruses What are Viruses? Virus—a nonliving particle made of a nucleic acid (DNA or RNA) and a protein coat called a capsid. Virology—study of viruses Living or Nonliving? Reasons viruses are NOT living organisms: Cannot grow, develop, or move (they are carried) Cannot reproduce on its own Viral Structure and Attachment Nucleic Acid Capsid A Bacteriophage ( a virus that only infects bacteria) Viral Structure and Attachment In general, viruses are species specific and some are cell type specific. – Species specific viruses can help control the spread of a viral disease (Ex. Smallpox) because they are more readily contained than viruses that can affect both animals and humans (Ex. Influenza aka “The Flu”) – The recognition and attachment process is like two pieces of a puzzle fitting together. Viral Replication Cycles 1. Lytic Cycle: when a virus uses the host cell’s energy to make new viruses and kills the cell in the process. 2. Lysogenic Cycle: when the virus’s nucleic acid is incorporated into the host cell’s chromosomes. Viral Replication Cycles Lytic viruses cause disease immediately Lysogenic viruses take longer to actively cause infection and they often reoccur: – Ex. herpes simplex I (causes cold sores in the mouth) and herpes simplex II (causes genital herpes). FYI: Lytic Cycle Chromosome Virus Host cell 1. Virus attaches to a host cell *ATTACHMENT* 4. New viruses bust out of the host cell, killing the host cell *INFECTION* 2. Virus injects its chromosome into the host cell *INCORPORATION* 3. The virus chromosome uses the host cell to make more viruses *REPLICATION* FYI: Lysogenic Cycle Virus Chromosome Host cell 1. Virus attaches to a host cell 4. When the cell reproduces, the provirus is copied as part of the chromosome 2. Virus injects its chromosome into the host cell 3. The virus chromosome is placed into the host cell’s chromosome. Provirus: viral genetic material that is placed into the host cell’s chromosome Releasing Viral Particles Exocytosis: the virus is packaged in small pieces of plasma membrane that fuse with the host cell’s plasma membrane, releasing viruses Sugar Step 1 Step 2 Host Cell Step 3 HIV Retroviruses are the most complex RNA viruses and they only involve RNA. Reverse transcriptase: an enzyme that makes DNA from the virus’s RNA (remember a virus is incorporated into the host cell’s DNA). HIV is a virus that infects white blood cell. HIV People may be infected, but show no signs of the disease because the host cell still functions normally. Spread by direct contact – Unprotected sex, blood transfusions, sharing needles for drugs **Most people with an HIV infection will eventually get AIDS because over time, more WBC’s become infected and die. Other Infectious Agents Viroid—smallest known particle that can cause infections – circular, single strands of RNA – no capsid (protein coat) Other Infectious Agents Prions—proteins that do not have any nucleic acids, but instead cause other proteins to fold incorrectly. – responsible for many animal diseases like mad cow disease and the human equivalent Creutzfeldt-Jakob disease. – ex. Kuru—occurred in many tribal places Other Viral Diseases Tobacco mosaic virus: first virus to be discovered (1930). common cold Hepatitis family (B & C are the most common in the US and can be sexually transmitted) Other Viral Diseases Ebola: 50-89% mortality; Biosafety Level (BSL) 4 –there are only a few found in the major countries of the world Prevention and Treatment 1. Interferons- proteins in the immune system that inhibit viral replication within other cells of the body 2. Vaccines- contain live or dead viruses and they trick the body into thinking it’s already infected. 3. Antiviral drugs- they are made to destroy viruses or to prevent viral replication. Treatment Antibiotics Generally WILL NOT WORK ON Viruses!!! Vaccination with Cowpox A cartoon satirizes British physician Edward Jenner, who is shown injecting patients with cowpox virus, resulting in their transformation into cows. Jenner lived from 1749 to 1823. His discovery that cowpox was an effective vaccine against smallpox was initially greeted with skepticism, but soon accepted. The procedure dramatically reduced the incidence of smallpox, once a major cause of death in the 18th century. Microsoft ® Encarta ® Encyclopedia 2004. © 1993-2003 Microsoft Corporation. All rights reserved. Kingdom Archaebacteria and Kingdom Eubacteria Prokaryote vs. Eukaryote Prokaryotic Cells Eukaryotic Cells No nucleus Has a nucleus Unicellular Unicellular or Multicellular No membrane bound organelles Membrane bound organelles Kingdoms Archaebacteria and Eubacteria Kingdoms Protista, Fungi, Plantae, and Animalia Prokaryotes Prokaryotes are classified into 2 different kingdoms: – Archaebacteria: live in extreme environments – Eubacteria: common bacteria that live almost everywhere Kingdom Archaebacteria Live in extreme habitats that are usually very low in oxygen Types of Archaebacteria 1. Methanogens—produce methane (a gas) –Live in marshes, lake sediment, digestive tracts, sewage treatment plants –Oxygen is a poison– need anaerobic conditions Kingdom Archaebacteria 2. Halophiles– like salty environments –Great Salt Lake, Dead Sea –use salt to make ATP (energy) 3. Thermophiles– live in hot, acidic sulfur springs and deep ocean vents Kingdom Eubacteria Live almost everywhere Some are heterotrophs: – Use organic molecules as food – Some are parasitic – Saphrophytes—organisms that feed on dead organisms or organic waste Kingdom Eubacteria Some are photosynthetic autotrophs: – use sunlight to carry out photosynthesis and make their own food Some are chemosynthetic autotrophs: – Carry out chemosynthesis: process of breaking down and releasing energy of inorganic compounds containing sulfur and nitrogen The Structure of Bacteria capsule pili DNA (chromosome) flagella The Structure of Bacteria Do not have a nucleus, but do have a cell wall, cell membrane, cytoplasm and ribosomes Some have a capsule: shell covering the cell wall that helps to protect the cell Some have pili: short hairlike structures on the surface of the cell that helps to hold onto host cells Many have flagella: whiplike structure on the surface of the cell that helps in movement Identifying Bacteria 1. Gram staining stains give bacteria color under a microscope – Gram staining is based upon the type of cell wall bacteria have: Gram positive bacteria stain purple Gram negative bacteria stain pink Importance: certain antibiotics only work on Gram positive bacteria while others only work on Gram negative bacteria Identifying Bacteria 2. By shape: 1. Rod (Bacilli) 2. Sphere (Cocci) 3. Spiral (Spiralla) Chains begin with the prefix strepto- Clusters begin with the prefix staphlo- Streptococci pyogenes: Necrotizing Fasciitis Facts: - If they get under the skin, they infect soft tissues and they are known as the flesh eating bacteria. -Approx 500-1500 cases a year in the US Vibrio cholerae: Cholera (a bacilli) Facts: -One of the most rapidly fatal diseases known -Found in contaminated water…how would it have gotten there??? -Last outbreak in the U.S. was back in 1911, but it’s still a problem in less developed countries Treponema pallidium: Syphillis (a spiralla) Facts: - A curable STD - If untreated, can cause serious damage to the body and deterioration in the brain, leading to madness or even death. Bacterial Reproduction Can’t reproduce by meiosis or mitosis because they don’t have a nucleus So, how do they do it??? 1. Binary fission: asexual reproduction because a bacterial cell copies itself 2. Conjugation: sexual reproduction because a bacterial cell connects to another bacterial cell through the pilus (plural, pili) and then transfers all or part of its DNA to the second bacterial cell Factors affecting growth Growing conditions must be right Obligate anaerobes– bacteria that cannot survive in presence of oxygen – Ex: Tetanus (Lock jaw): puncture wound deep into skin provides oxygen-free environment for this bacteria Facultative anaerobes– can live with or without oxygen – Ex: E. coli in intestines Obligate aerobes– bacteria that can’t survive without oxygen. – Ex: bacteria that causes TB Survival Under unfavorable conditions, some bacteria form endospores Endospore—structure that contains bacterium’s DNA and cytoplasm. Covered by tough outer protective coating. – Resting stage—no reproduction Survival – When conditions improve, endospore will germinate/reproduce Example: When canning foods, we must sterilize jars and acidify food prevents food poisoning with botulism Example: Tetanus forms endospores. When spore enters body through wound, will germinate and release toxins that lead to neurological problems. Helpful Bacteria Uses: – Sewage treatment plants—break down wastes – Food processing—bacteria create buttermilk, sour cream, yogurt, cheese, sauerkraut, some pickles – Chemicals—insecticides, clean up oil spills, genetic engineering (making insulin) – Nitrogen fixation—can take nitrogen gas and put it into useful compounds