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Bacteria Bacteria (bacterium, singular), microorganisms that lack a nucleus (prokaryote) and have a cell wall Bacteria are the most common organisms on earth but they can not be seen. However, colonies of bacteria, such as those found on a laboratory culture plate, can be viewed easily without a microscope. Bacteria Structure Bacteria Placed in two domains, 1) Domain Bacteria (typical bacteria) and 2) Archae (ancient bacteria). Bacteria are placed in these domains depending on the make up of their cell membrane and cell wall. Bacteria Bacteria are often classified on the basis of their physical shapes: bacteria can be spherical (cocci), rod-shaped (bacilli), or corkscrew-shaped (spirochetes). Prefixes may be used: diplo means two staphlo means clusters strepto means chains Bacteria This scanning electron micrograph shows disease-causing Streptococcus bacteria, commonly found in the human mouth, throat, respiratory tract, bloodstream, and wounds. Often airborne in hospitals, schools, and other public places, Streptococcus bacteria are responsible for infections such as strep throat, scarlet fever, and some types of pneumonia. "Streptococcus Bacteria," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved. Bacteria Another classification system divides bacteria into gram-negative or gram-positive according to the composition of their cell walls, a distinction identified by a staining technique called the Gram stain. Bacteria that require oxygen are called aerobic bacteria, or aerobes. Bacteria that live without oxygen are called anaerobic bacteria, or anaerobes. Bacteria: Reproduction http://www.wwnorton.com/college/biology/mbio/animations/dna_replication.asp A bacterium reproduces by means of a process called binary fission. Like all cells, bacteria contain genetic material known as deoxyribonucleic acid (DNA). However, the DNA of bacteria is arranged in a single circular chromosome. Bacteria also often have additional DNA in the form of smaller rings called plasmids. In binary fission, the single chromosome is replicated, the bacteria divides into two cells, and each cell receives one chromosome. The two cells are thus genetically identical. http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter11/animation_quiz_1_.html Bacteria: Genetic Diversity Bacteria shuffle DNA between cells by several processes, including transformation, conjugation, and transduction to gain genetic diversity. Through mixing genetic material, bacteria develop new traits, including the ability to withstand changes in acidity and temperature, and resistance to antibiotics. Bacteria: Genetic Diversity In transformation, bacteria take up fragments of DNA released into the soil or water as dead bacteria are decomposed.http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_1.html In conjugation, a donor bacterium attaches itself to a recipient bacterium, generates a tube called a pilus, and transfers fragments of plasmid DNA to the recipient.http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_3.html Transduction involves the transfer of DNA fragments between bacteria cells by a bacteriophage, a virus that infects bacteria. http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_2.html http://learn.genetics.utah.edu/content/begin/cells/scale/ Virus Virus, infectious agent found in virtually all life forms, including humans, animals, plants, fungi, and bacteria. Viruses consist of genetic material—either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA)—surrounded by a protective coating of protein, called a capsid. Viruses are between 20 and 100 times smaller than bacteria. Viruses are not considered free-living, since they cannot reproduce outside of a living cell. They have evolved to transmit their genetic information from one cell to another for the purpose of replication. Although many infectious diseases, such as the common cold, are caused by viruses, there are no cures for these illnesses. Individual viruses, or virus particles, also called virions, contain genetic material, or genomes, in one of several forms. The most elaborate viruses are the bacteriophages, which use bacteria as their hosts. Virus http://highered.mcgraw-hill.com/olc/dl/120088/micro41.swf Viral Replication http://www.cellsalive.com/phage.htm http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter17/animation_quiz_2.html Immune System Immune System, group of cells, molecules, and organs that act together to defend the body against foreign invaders that may cause disease, such as bacteria, viruses, and fungi. The disease resistance provided by these systems is called immunity. There are two types of immunity: innate and adaptive. Innate, or nonspecific, immunity is the body’s first, generalized line of defense against all invaders. Innate Immunity Innate immunity is furnished by 1)barriers such as skin, tears, mucus, and saliva 2)the rapid inflammation of tissues that takes place shortly after injury or infection. When an injury occurs, chemical messengers called histamines are released. Histamines increase blood flow to the area and increase permeability of the surrounding capillaries, allowing more white cells into the area. Adaptive Immunity If an invader gets past this first line of defense, the immune system develop specifically tailored defenses against the invader. The immune system can call upon these defenses whenever this particular invader attacks again in the future. These specifically adapted defenses are known as adaptive, or specific, immunity. Adaptive immunity Adaptive immunity has four distinguishing properties: 1) It responds only after the invader is present. 2) It is specific, tailoring each response to act only on a specific type of invader. 3) It displays memory, responding better after the first exposure to an invader, even if the second exposure is years later. 4) It does not usually attack normal body components, only those substances it recognizes as nonself. White blood cells:macrophage White blood cells play an important role in the immune system. Some white blood cells, known as macrophages and neutrophils, play a function in innate immunity by surrounding, ingesting, and destroying invading bacteria and other foreign organisms in a process called phagocytosis (literally, "cell eating"), which is part of the inflammatory reaction. Immune Responses: Two Kinds Adaptive immune responses are actually reactions of the immune system to structures on the surface of the invading organism called antigens. There are two types of adaptive immune responses: 1) humoral 2) cell mediated. White blood cells:Lymphocytes Lymphocytes are specialized white blood cells whose function is to identify and destroy invaders. All lymphocytes begin in the bone marrow, the soft tissue that fills most bone cavities, but they mature in two different places (bone marrow or thymus gland. Lymph nodes are located throughout the body and contain large numbers of white blood cells. They filter pathogens (disease-causing agents). and expose them to white blood cells. The spleen, an organ behind the stomach, filters pathogens from the blood. White blood cells: T Cells Helper T lymphocytes, regulate the immune system by controlling the strength and quality of all immune responses. Each lymphocyte, as it matures, makes an antigen receptor—that is, a specific structure on its surface that can bind with a matching structure on the antigen like a lock and key. Immune Responses: Humoral Humoral immune responses resist invaders that act outside of cells, such as bacteria and toxins (poisonous substances produced by living organisms). Humoral immune responses can also prevent viruses from entering cells. White blood cells:B Cells Some lymphocytes mature in the bone marrow and are called B lymphocytes. During humoral immune responses, B lymphocytes, or B cells, make antibodies, which circulate through the blood and other body fluids, binding to antigens and helping to destroy them. Humoral Immune Response First, macrophages take up some of the antigen and attach it to transport molecules, which then present the antigen to T helper cells. The interleukins in turn activate any B lymphocytes that have also bound the antigen. The activated B cells then divide and differentiate into plasma cells which secrete antibodies. Finally, the secreted antibodies bind the antigen and help destroy it. Antibodies Antibodies are Y-shaped proteins. The antibody binds to the antigen at the ends of the arms of the Y. Antibodies can sometimes stop an antigen’s disease-causing activities simply by neutralization—that is, by binding the antigen and preventing it from interfering with the cell’s normal activities. Antibodies also help destroy antigens by preparing them for ingestion by macrophages. White blood cells:T Cells Other lymphocytes, called T lymphocytes, or T cells, mature in the thymus, a small glandular organ located behind the breastbone. Some T lymphocytes, called cytotoxic (cellpoisoning) or killer T lymphocytes, generate cellmediated immune responses, directly destroying cells that have specific antigens on their surface that are recognized by the killer T cells. Suppressor T cells help to shut down the immune response after the pathogen is cleared from the body. When the body is first exposed to an antigen, several days pass before the adaptive immune response becomes active. Immune activity then rises, levels off, and falls. During following exposures to the same antigen, the immune system responds much more quickly and reaches higher levels. This is because Memory Cells remain in the body. Memory cells will recognize the pathogen and begin to divide rapidly, eliminating the pathogen before it can produce disease. This complete resistance to disease is called immunity and may be achieved through either active or passive immunization. Active immunization occurs when a person’s own immune system is activated and generates a primary immune response. Active immunization can be triggered in two ways, either by natural immunization or by vaccination. Natural immunization In natural immunization, the body contracts a disease and recovers. After having had the disease once, a person is no longer susceptible to it. Vaccination Vaccination is intentional immunization against a particular disease by the use of vaccines, substances that are structurally similar to the actual disease-producing agents but that do not produce disease themselves. The first type of vaccine, contains chemically killed bacteria or other pathogenic organisms. The other type, such as the oral polio vaccine, contains weakened forms of living organisms that have been genetically selected so they do not produce disease. Passive immunization Passive immunization does not engage the person’s own immune system. Instead, the individual receives antibodies that were created in another person or animal. This is temporary immunity. Immune System Disorders Disorders of the immune system can range from the less serious, such as mild allergy, to the life threatening, such as more serious allergy, transplant rejection, immune deficiencies, and autoimmune diseases. Allergic Reactions Allergy, sometimes called hypersensitivity, is caused by immune responses to some antigens. Antigens that provoke an allergic response are known as allergens. Allergic Reactions These immediate hypersensitivity reactions result from the production of antibodies when a person is first exposed to an allergen. The antibodies become attached to mast cells— white blood cells containing histamine, the chemical that causes the familiar allergic symptoms of runny nose, watery eyes, and sneezing. Allergic Reactions Mast cells are particularly abundant in the lungs and intestine. If the antigen-binding sites of mast cells become filled with an allergen, the mast cells release histamine. Organ Transplant The immune system recognizes and attacks anything different from the substances normally present within an individual, even substances that are only slightly different, such as transplanted tissues and organs. Organ Transplant To minimize the chances of transplant rejection, physicians seek transplant donors who share as many genes as possible with the transplant recipient. Even then, most transplant recipients are given drugs to suppress their immune response and prevent rejection of the transplant. Immune Deficiencies Deficiencies in immune function may be either inherited or acquired. An infectious agent resulting in fatal immune deficiency is the human immunodeficiency virus (HIV). This virus causes acquired immune deficiency syndrome (AIDS) by infecting and eventually destroying helper T cells. Autoimmune Disease Autoimmunity is the immune response of the body turned against its own cells and tissues.