4/7/2007. Key Concepts: Viruses, Bacteria and Diseases: Are We Ahead of Them? Objectives:

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1 Viruses, Bacteria and Diseases: Are We Ahead of Them? Objectives: 1. To learn the basic structures of viruses. 2. To understand the life cycles of viruses. 3. To learn the differences between various species of bacteria. 4. To learn fundamental biological principles regarding bacteria. Key Concepts: A virus can have one of several different structures. A virus does not necessarily cause a disease - it can be lytic or lysogenic. There are many different viruses which cause human diseases. Bacteria are classified according to the morphological configuration which they have. The gram stain differentiates between the two types of cell walls found in bacteria. Bacteria can produce toxins. of viruses -- A virus is a nucleic acid (usually RNA) which is surrounded by a protein coat. Viruses are much smaller than bacteria and are obligate intracellular parasites. -- The head of a virus is composed of small units called capsids. Some viruses have glycoprotein structures which are spikes that aid in attachment. Viruses comes in three basic shapes: (1) helical: rod-shaped (2) polyhedral: many sides (example: polio) (3) mixed: (example: bacteriophage) The tobacco mosaic virus is helical, while the influenza and the adenovirus are polyhedral. Some viruses and their effects. (a) Particles of a DNA virus that causes a herpes infection in humans. (b) Particles of an enveloped RNA virus that causes influenza in humans. (c) Streaking of a tulip blossom. A harmless virus infected pigment-forming cells in the colorless parts. (d) An orchid leaf infected by a rhabdovirus. Label the structures below. Draw any capsomeres which have been deleted. Where would the RNA be in each of these drawings? 1

2 Paramecium infected bacterial cell A. Lytic Cycle one virus particle A. Lysogenic Cycle A. Lytic and Lysogenic Cycles The Two Cycles of a Virus Summary of Viral Multiplication Cycles B. Multiplication Cycle of an Animal Virus Includes 5 basic steps: (1) Attachment (2) Penetration (3) Replication (4) Assembly (5) Release 2

3 I Common Viruses C. Three types of viral infections 1. New viral production a. AIDS b. ebola 2. Latent infection (silent infection) a. herpes simplex I (cold sores) b. shingles 3. Tumor a. cancer b. warts I Common Viruses Some viruses can actually be carried by insects. Organisms like this are called vectors. Yellow fever, for example is carried by a mosquito. Some plant diseases are transmitted in the same manner. The curly disease in sugarbeets is an example Bacteria and Diseases: Are We Ahead of Them? I. Shape The shape of bacteria is often useful in differentiating between species. For example a bacillus is so named because of its rod shaped appearance. There are several different configurations which a bacteria can have. These are dependent upon the plane in which the bacteria divides. The Cell Wall and the Gram Stain The Cell Wall and the Gram Stain gram The gram stain is a differential stain which divides all bacteria into 2 categories. The first category is positive and the second is gram negative. These two categories exist due to differences in the cell wall. In gram positive bacteria, there is a large layer of peptidoglycan, a sugar polymer cross-linked with proteins which covers the plasma membrane. 3

4 I by cell Toxins There are two types of toxins. List them: a. exotoxin -- poisonous substance secreted certain bacteria b. endotoxin -- poisonous component of the walls of certain bacteria. Fill out the chart below regarding toxins Exotoxins: A protein synthesized by the cell and liberated in medium (botulism) Very potent: 1 gram of botulinum toxin can kill a million people Denatured by heat Endotoxins: Released only when the bacteria die (salmonella) Mildly potent; potent pyrogen (i.e., causes fever) Can denature with heat IV. Bacterial Growth Bacteria compete by outgrowing other cells. Bacteria can colonize wide ranges of habitats such as ph extremes, temperature extremes or salinity extremes. What are some adaptations that bacteria would have to make in order to live at such extremes? (Hint: Remember what the plasma membrane is composed of?) Psychrophiles live in cold conditions. Mesophiles live in moderate conditions. Thermophiles live in hot conditions. IV. Bacterial Growth Bacterial growth is exponential. The formula is N t = N 0 2 kt where N t = the number of organisms at a certain period of time N 0 = the original number of organisms k = the intrinsic rate of growth t = amount of time which has passed 2 = each generation, the number of organisms double I inoculate one bacterial cell into a culture medium. If the intrinsic rate of growth is 3 generations/hour and two hours have passed, how many organisms do you now have? V. Nutrients Carbon Source Autotrophs - carbon dioxide is the sole or principle biosynthetic carbon source Heterotrophs - metabolize organic Energy Source Phototrophs - light Chemotrophs - oxidation of organic or inorganic Hydrogen or Electron Source Lithotrophs - reduced inorganic Organotrophs - organic VI. Kochs Postulates The rules used in microbiology to determine if a specific organism causes a specific disease. 1. The organism must be present in every case and absent from all healthy organisms. 2. You must be able to isolate and grow the organism in a culture. 3. If injected into a healthy animal the organism must cause the same disease. 4. You must be able to recover the organism from the injected animal. 4

5 V Bacteria and Antibiotics VI 1. Antibiotics work on bacteria and not people because they destroy the ribosomes/ peptidoglycans of the bacteria. This is why penicillin is often so effective against gram positive bacteria. 2. Antibiotics sometimes do not work on diseasecausing bacteria because we overuse them. 1. The genus Rhizobium is essential for nitrogen fixation. Examples of plants that do this include alfalfa, clover, peas, green beans, and soybeans. This relationship between the bacterium and the plant is referred to as symbiosis. Soybean roots: -- non-nodulated on left -- nodulated on right VI VI 3. Some bacteria are produced to be used in cleaning up oil spills, and therefore are extremely important in keeping the ecosystem clean. 4. Can you think of other uses? 1. The genus Rhizobium is essential for nitrogen fixation. Examples of plants that do this include alfalfa, clover, peas, green beans, and soybeans. This relationship between the bacterium and the plant is referred to as symbiosis. 2. Many bacteria play key roles as decomposers and by doing this they are responsible for recycling of key elements such as carbon, nitrogen, phosphorous, and sulfur. 5