Protists & Pathogen Disease Federoff. Bacterial Diseases –Microorganisms—viruses and...
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Transcript of Protists & Pathogen Disease Federoff. Bacterial Diseases –Microorganisms—viruses and...
![Page 1: Protists & Pathogen Disease Federoff. Bacterial Diseases –Microorganisms—viruses and prokaryotes—that cause disease are called pathogens. –Louis Pasteur.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d885503460f94a6d2be/html5/thumbnails/1.jpg)
Protists & Pathogen Disease
Federoff
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Bacterial Diseases
– Microorganisms—viruses and prokaryotes—that cause disease are called pathogens.
– Louis Pasteur helped to establish what has become known as the germ theory of disease when he showed that bacteria were responsible for a number of human and animal diseases.
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Disease Mechanisms
– Bacteria produce disease in one of two general ways.
– Some bacteria destroy living cells and tissues of the infected organism directly, while some cause tissue damage when they provoke a response from the immune system.
– Other bacteria release toxins (poisons) that interfere with the normal activity of the host.
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Disease Mechanisms
Another organism
Human Contact
An object
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Damaging Host Tissue
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Releasing Toxins
– Bacteria that produce toxins include the species that causes diphtheria, and the species responsible for a deadly form of food poisoning known as botulism.
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Controlling Bacteria
– Although most bacteria are harmless, and many are beneficial, the everyday risks of any person acquiring a bacterial infection are great enough to warrant efforts to control bacterial growth.
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Physical Removal
– Washing hands or other surfaces with soap under running water doesn’t kill pathogens, but it helps dislodge both bacteria and viruses.
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Disinfectants
– Chemical solutions that kill bacteria can be used to clean bathrooms, kitchens, hospital rooms, and other places where bacteria may flourish.
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Food Storage
– Low temperatures, like those inside a refrigerator, will slow the growth of bacteria and keep most foods fresher for a longer period of time than possible at room temperature.
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Food Processing
– Boiling, frying, or steaming can sterilize many kinds of food by raising the temperature of the food to a point where bacteria are killed.
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Sterilization by Heat
– Sterilization of objects such as medical instruments at temperatures well above 100° Celsius can prevent the growth of potentially dangerous bacteria.
– Most bacteria cannot survive such temperatures.
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Preventing Bacterial Diseases
– Many bacterial diseases can be prevented by stimulating the body’s immune system with vaccines.
– A vaccine is a preparation of weakened or killed pathogens or inactivated toxins.
– When injected into the body, a vaccine prompts the body to produce immunity to a specific disease.
– Immunity is the body’s ability to destroy pathogens or inactivated toxins.
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Treating Bacterial Diseases
– A number of drugs can be used to attack a bacterial infection. These drugs include antibiotics--such as penicillin and tetracycline--that block the growth and reproduction of bacteria.
– Antibiotics disrupt proteins or cell processes that are specific to bacterial cells. In this way, they do not harm the host’s cells.
– Antibiotics are not effective against viral infections.
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Viral Diseases
– Like bacteria, viruses produce disease by disrupting the body’s normal homeostasis.
– Viruses produce serious animal and plant diseases as well.
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Viral Diseases
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Disease Mechanisms – In many viral infections, viruses attack and
destroy certain cells in the body, causing the symptoms of the associated disease.
– Poliovirus, for example, destroys cells in the nervous system, producing paralysis.
– Other viruses cause infected cells to change their patterns of growth and development, sometimes leading to cancer.
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Preventing Viral Diseases
– In most cases, the best way to protect against most viral diseases lies in prevention, often by the use of vaccines.
– Many vaccines have been developed in the last three centuries. Today, there are vaccines against more than two dozen infectious diseases.
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INNOVATIONS IN VACCINES
– 1769 Edward Jenner performs the first inoculation against smallpox, using the less harmful but similar cowpox virus.
– 1880s Louis Pasteur develops vaccines against anthrax and rabies.
– 1923 Albert Calmette and Camille Guerin develop a vaccine against tuberculosis.
Before vaccine development, the Red Cross made the public aware of the threat of tuberculosis using posters such as this one, circa 1919.
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INNOVATIONS IN VACCINES
– 1950s Jonas Salk develops a polio vaccine that uses killed viruses. Albert Sabin develops a polio vaccine that uses weakened viruses.
– Before the advent of the polio vaccine, hospitals were filled with polio-stricken children in machines called iron lungs, which helped them breathe.
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INNOVATIONS IN VACCINES
– 1981 A vaccine against hepatitis B that uses recombinant DNA gains government approval.
– 2006 A vaccine against human papillomavirus, a virus known to cause certain cancers, gains approval.
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Preventing Viral Diseases
– Effective ways to help prevent infection include washing your hands frequently, avoiding contact with sick individuals, and coughing or sneezing into a tissue or your sleeve, not into your hands.
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Treating Viral Diseases
– Unlike bacterial diseases, viral diseases cannot be treated with antibiotics.
– In recent years, limited progress has been made in developing a handful of antiviral drugs that attack specific viral enzymes that host cells do not have.
– These treatments include an antiviral medication that can help speed recovery from the flu virus and another that may—in certain instances—prevent HIV.
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Emerging Diseases
– An unknown disease that appears in a population for the first time or a well-known disease that suddenly becomes harder to control is called an emerging disease.
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Emerging Diseases
– In recent years, new diseases, such as severe acute respiratory syndrome (SARS) in Asia, have appeared. At the same time, some diseases thought to be under control have come back.
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Emerging Diseases
– Changes in lifestyle and commerce have made emerging diseases even more of a threat.
– Human populations that were once isolated by oceans and mountain ranges are now in close contact with more developed parts of the world.
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“Superbugs”
– When first introduced in the 1940s, penicillin, an antibiotic derived from fungi, was a miracle drug. Patients suffering from life-threatening infections were cured almost immediately by this powerful new drug.
– Within a few decades, however, penicillin lost much of its effectiveness, as have other, more current antibiotics.
– The culprit is evolution.
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“Superbugs”
– The widespread use of antibiotics has led to a process of natural selection that favors the emergence of resistance to these powerful drugs.
– Physicians now must fight “superbugs” that are resistant to whole groups of antibiotics and that transfer drug-resistant genes from one bacterium to another through conjugation.
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“Superbugs”
– An especially dangerous form of multiple drug resistance has recently appeared in a common bacterium. Methicillin-resistant Staphylococcus aureus, known as MRSA, can cause infections that are especially difficult to control.
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“Superbugs”
– Infection by MRSA can be very serious or fatal for people in hospitals and nursing homes who have weakened immune systems.
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New Viruses
– Because viruses replicate so quickly, their genetic makeup can change rapidly, sometimes allowing a virus to jump from one host species to another.
– Researchers have evidence that this is how the virus that causes AIDS originated, moving from nonhuman primates into humans.
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New Viruses
– Public health officials are especially worried about the flu virus.
– Only very slight genetic changes may be needed for the bird flu virus to make the jump to humans, where there would be little natural resistance to it.
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Prions
– Prions are misfolded proteins in the brain that cause a chain reaction of misfolding in other normal proteins they contact, eventually clogging the brain tissue and causing disease.
– Many animals, including humans, can become infected with prions.
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Prions
– In 1972, Stanley Prusiner became interested in scrapie, an infectious disease in sheep, the exact cause of which was unknown.
– Experiments revealed clumps of tiny protein particles in the brains of infected sheep. Prusiner called these particles prions, short for “protein infectious particles.”
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Prions
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PROTISTS
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The First Eukaryotes
– More than a billion years ago, the first eukaryotes appeared on Earth.
– Single-celled eukaryotes are still with us today and are often called “protists”—a name that means “first.” Traditionally, protists are classified as members of the kingdom Protista.
– Protists are eukaryotes that are not members of the plant, animal, or fungi kingdoms.
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The First Eukaryotes
– Although most protists are unicellular, quite a few are not. Brown algae called kelp are the largest protists. They contain millions of cells arranged in differentiated tissues.
– Kelp are considered protists because they are related more closely to certain unicellular protists than to members of any other kingdom.
– Otters wrap themselves in giant kelp to keep from drifting out to sea while they sleep.
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The “Protist” Dilemma
– Biologists have discovered that “protists” display a far greater degree of diversity than any other eukaryotic kingdom.
– Euglena, brown algae, diatoms, and slime molds are examples of protists.
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The “Protist” Dilemma
– In addition to their diversity, biologists also found that many “protists” are far more closely related to members of other eukaryotic kingdoms than they are to other “protists.”
– By definition, the members of a living kingdom should be more like one another than like members of other kingdoms. This is not true of protists, which means that reclassification is necessary.
– In the past, scientists sorted protists into three groups: plantlike protists, animal-like protists, and funguslike protists. However, this solution began to fail as biologists learned that many protists do not fit into any of these groups.
– Biologists also discovered that many of the animal-like and funguslike protists are so similar that they belong in a single group, not two.
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Multiple Kingdoms?
• The most recent studies of protists divide them into six major clades, each of which could be considered a kingdom.
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Multiple Kingdoms?
– This cladogram represents an understanding of protist relationships supported by current research.
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Multiple Kingdoms?
– Surprisingly, the plant, animal, and fungi kingdoms fit right into these six clades. Animals and fungi actually emerge from the same protist ancestors.
– Protists were the first eukaryotes, and evolution has had far more time to develop differences among protists than among more recently evolved eukaryotes like plants and animals.
– By finding the fundamental divisions among protists, we also identify the most basic differences among all eukaryotes.
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What “Protist” Means Today
– Biologists assembling the Tree of Life favor the classification shown in the cladogram.
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What “Protist” Means Today
– Even though the biologist building the Tree of Life prefer a different classification, the word “protist” remains in common usage, even among scientists.
– Bear in mind that “protists” are not a single kingdom but a collection of organisms that includes several distinct clades.
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Amoeboid Movement
– Many unicellular protists move by changing their shape, a process that makes use of cytoplasmic projections known as pseudopods. The cytoplasm of the amoeba, for example, streams into the pseudopod and the rest of the cell follows.
– This type of locomotion is called amoeboid movement and is found in many protists.
– Amoeboid movement is powered by a cytoskeletal protein called actin. Actin also plays a role in the muscle contractions of animals.
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Cilia and Flagella
– Many protists move by means of cilia and flagella, structures supported by microtubules. Cilia are short and numerous, and they move somewhat like oars on a boat.
– Flagella are relatively long and usually number only one or two per cell. Some flagella spin like tiny propellers, but most produce a wavelike motion from base to tip.
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Cilia and Flagella
– Protists that move using cilia are known as ciliates, and those that move with flagella are called flagellates.
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Passive Movement
– Some protists are nonmotile—they depend on air or water currents and other organisms to carry them around.
– These protists form reproductive cells called spores that can enter the cells of other organisms and live as parasites.
– Spore-forming protists include Plasmodium, which is carried by mosquitoes and causes malaria, and Cryptosporidium, which spreads through contaminated drinking water and causes severe intestinal disease.
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Cell Division
– Amoebas, and many other protists, reproduce by mitosis: They duplicate their genetic material and then divide into two genetically identical cells.
– Mitosis enables protists to reproduce rapidly, especially under ideal conditions, but it produces cells that are genetically identical to the parent cell, and thus limits the development of genetic diversity.
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Conjugation
– Paramecia and most ciliates reproduce asexually by mitotic cell division.
– However, under stress, paramecia can remake themselves through conjugation—a process in which two organisms exchange genetic material.
– After conjugating, the cells then reproduce by mitosis.
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Conjugation
– Paramecium has two types of nuclei: a macronucleus and one or more smaller micronuclei.
– The micronucleus holds a “reserve copy” of every gene in the cell.
– The macronucleus has multiple copies of the genes the cell uses in its day-to-day activities.
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Conjugation
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Conjugation
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Conjugation
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Conjugation
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Conjugation
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Conjugation
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Conjugation
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Conjugation
– Conjugation is not a type of reproduction because no new individuals are formed.
– Conjugation is, however, a sexual process because new combinations of genetic information are produced.
– In a large population, conjugation helps produce and maintain genetic diversity.
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Sexual Reproduction
– Many protists have complex sexual life cycles in which they alternate between a diploid and a haploid phase, a process known as alternation of generations.
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Sexual Reproduction
– A water mold is an example of a protist that undergoes alternation of generations.
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Sexual Reproduction
– Water molds grow into long branching filaments consisting of many cells formed by mitotic cell division.
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Sexual Reproduction
– Water molds reproduce asexually by producing spores in a structure called a sporangium.
– In water molds the spores are flagellated.
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Sexual Reproduction
– Water molds also reproduce sexually by undergoing meiosis and forming male and female structures.
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Sexual Reproduction
– The male and female structures produce haploid nuclei that fuse during fertilization, forming a zygote that begins a new life cycle.