Chapter 19 Biology Notes PDF

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Philip Raven Mrs. Jamerlan Biology I (Period 3) 2 March 2013 Biology Chapter 19 Outline I.

Characteristics of Prokaryotic Cells A. Cell Sizes, Shapes, and Structures 1. The average prokaryotic cell is no longer or wider than 0.5 to 1 micrometer. 2. The most common cell shapes are: i. A sphere (coccus) ii. A rod (bacillus) iii. A spiral (spirillum) 3. Almost all prokaryotes have a semi rigid porous cell wall around their plasma membrane. 4. A sticky, secreted layer of slime coats the wall of many bacteria and helps them stick to surfaces. 5. Prokaryotic flagella have are built differently than eukaryotic flagella. They have no microtubules and do not bend side to side, but instead rotate. B. Metabolic Diversity 1. Prokaryotes require energy to make energy (ATP), and carbon atoms to make sugar and other organic compounds. 2. Some prokaryotes are autotrophs, or self-feeders. They get carbon from CO2. 3. The photoautotrophs get energy from sunlight. The chemoautotrophs get energy by releasing electrons from a great variety of mostly inorganic substances. 4. Heterotrophs are not self-feeders. They get carbon from organic compounds made by other organisms and use it to make organic compounds of their own. 5. Photoheterotrophs get energy from the sun. Chemoheterotrophs get carbon and energy from tissues, wastes, or remains of other organisms. Most chemoheterotrophs act as parasites and feed of a living host. C. Prokaryotic Cell Characteristics 1. No nucleus; chromosome in nucleoid 2. Generally a single chromosome (a circular DNA molecule); many species also contain plasmids. 3. Cell wall present in most species 4. Reproduction mainly by prokaryotic fission 5. Collectively, great metabolic diversity among species.

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D. Reproduction and Gene Transfers 1. Some types of prokaryotes can divide every twenty minutes. Before each cell divides, it doubles in size. Each daughter cell has one copy of the prokaryotic chromosome- a circular double-stranded molecule of DNA with a few proteins. 2. A cell can reproduce from a prokaryotic fission. For a short time, a parent cell replicates its single chromosome, and this DNA replica attaches to the plasma membrane adjacent to the parent molecule. 3. Besides inheriting DNA “vertically” from a parent cell, prokaryotes engage in horizontal gene transfers: they pick up genes from cells of the same or different species. One mechanism of horizontal gene transfer is conjugation, which requires contact with a cell that makes a sex pilus, which is a “hairlike” extension from a microbe and it functions in attachment. E. Classification and Phylogeny 1. Numerical taxonomy has dominated classification efforts of prokaryotic fossils. 2. The more traits two groups share, the closer is the inferred relatedness. The Bacteria A. Representative Diversity 1. The first cells evolved as unstable crustal plates were colliding and forming the proto-continents. 2. Photosynthesis evolved in many bacterial lineages. Only cyanobacteria release free oxygen by a noncyclic pathway however. 3. When nitrogen is scarce, some cells in the chain develop into heterocysts. They carry out nitrogen fixation, a process that converts gaseous nitrogen into ammonia (NH3). The cells of most species cannot utilize gaseous nitrogen because they cannot break its triple bond. The ability of heterocysts to do so gives cyanobacteria a big competive advantage in nitrogen-poor environ,ents. 4. Species in the proteobacteria group are pathogens. A pathogen is a disease-causing agent that infects a host organism and lives in or on it. Disease occurs when a pathogen’s metabolic activites disrupt host function. 5. Chlamydias are intracellular parasites of animals. They cannot make ATP, but obtain it from host cells. 6. Gram-positive bacteria include diverse lineages. All have a thick wall that retains purple dye if prepared for microscopy using the Gram-staining technique. 7. Spirochetes resemble stretched-out springs. Some are free-living; others live inside a host organism. The Archaeans A. The Third Domain 1. Archaeans and bacteria look alike in size and shape, neither have a nucleus and both have one circular chromosome, with some of the genes arranged as operons. 2. The three-domain system is now widely accepted, and evidence that supports it is accumulating. It turns out that the archaeans and bacteria have different cell wall components.

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B. Here, There, Everywhere 1. Most archaeans are methanogens (methane producers), extreme halophiles (salt lovers), and extreme thermophiles (heat lovers). These three informal designations are not phylogenetic groupings. Archaeans and bacteria often coexist, and they often exchange genes. 2. Methanogens produce 2 billion tons of methane annually. The release of this carbon-containing gas into the air has a major impact on the global carbon cycle. 3. Extreme halophilic archaeans live in the Dead Sea, the Great Salt Lake, saltwater evaporation ponds, and other highly salty habitats. 4. Extreme thermpohilic archaeans live beside hydrothermal vents, where temperatures can go to more than 100 C. These archaeans use hydrogen sulfide escaping from the vents as an electron source for ATP- forming reactions. 5. Archaeans are common in the seas- and not just at vents. There may be as many archaeans in deep water as there are bacteria in water near the ocean’s surface. The Viruses A. The Structure of Virus Particles 1. A virus is a noncellular infectious particle consisting of DNA or RNA, or few enzymes, and a protein coat. A virus cannot multiply by itself. In an act of molecular piracy, its genes direct a host cell to make building blocks that can be assembled into new virus particles. B. Viral Multiplication 1. A lytic pathway, the steps of attachment through assembly occur fast, and lysis follows. Here lysis refers to the disintegration of a host cell plasma membrane, wall, or both, which lets the cytoplasm-and virus particles- dribble out. The host synthesized a viral enzyme that initiated lysis, and its own death. 2. In a lysogonic pathway, a virus enters a latent state that extends the multiplication cycle. Viral genes get integrated into the host chromosome. The recombination molecule is passed along to all the descendents of the host cell, 3. Latency is typical of many virus, such as type I Herpes simplex, which causes cold sores. The virus infects nerve cells. When stress or sunburn reactivates it, the virus moves to the skin and causes painful lesions. Viroids and Prions 1. Theodor Diener announced the discovery of a new type of pathogen. It was a small circle of RNA without any protective protein coat. He named it a viroid, because it seemed like a stripped-down version of a virus. 2. Neurologist Stanly Prusiners research began after he watched helplessly as one of his patients died of Creutzfeldt-Jakob Disease. This disease caused dementia and death. Prusiner proposed that proteins called prions are present in a normal nervous system, where they fold in a characteristic way. Disease develops after they fold in a characteristic way.

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Evolution and Disease A. The Nature of Disease 1. While in the infection stage, a pathogen multiplies in either the cells or tissues of the host. Disease may result, depending on whether the defense ( immune system) works. 2. Contagious diseases like the common cold spread by contact through: i. Mucus ii. Blood iii. Or other fluid from an infected individual. 3. Epidemic- a disease that spreads through part of a population for a limited time, then subsides. A pandemic may occur if the epidemic of the same disease break out in different geographic region at the same time. 4. A pathogen will result only as long as it can gain entry to the energy and raw materials. 5. Usually, an individual will die only if it becomes host to multiple pathogens. 6. Ebola kills 70 to 90 percent of people it infects. 7. H5N1 virus strain of influenza infected and killed more than 170 people. B. Drug-Resistant Pathogens 1. Penicillin is the 1st antibiotic drug manufactured synthetically and put to wide use. It saved many lives during WWII. C. The Eight Deadliest Infectious diseases 1. Acute Respiratory Infections (pneumonia, influenza)- bacteria, viruses 2. Diarrheas ( Amoebic dysentery)- Bacteria, viruses, protists 3. Tuberculosis- Bacteria 4. Malaria- protists 5. Aids-virus (HIV) 6. Measles-viruses 7. Hepatitis B- virus 8. Tetanus- bacteria...