Chapter 6: An Introduction to Viruses, Viriods, and Prions PDF

Chapter 6 An Introduction to Viruses, Viriods, and Prions Lecture Outline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. © McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No re...

Chapter 6 An Introduction to Viruses, Viriods, and Prions Lecture Outline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. © McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  The Search for the Elusive Virus Louis Pasteur: postulated that rabies was caused by a “living thing” smaller than bacteria (1884)(he also said that there’s something smaller than a bacteria). Dmitri Ivanoski: first proposed the term “virus” (L. “poison”). (he came up with the word “virus”. Virus means “poison”. Ivanovski and Beijerinck: showed a disease in tobacco was caused by a virus (1890s). 1950s: virology was a multifaceted discipline: – Viruses: noncellular particles with a definite size, shape, and chemical composition. In 1950s virus started being studied. They are not living things; They can’t do anything by themselves. They take advantage of the host and do harm!!. – Made of either a piece of DNA or piece of RNA, covered by a protein. – SMALLER THAN BACTERA AND ANYTHIN ELSE!!! 6-2 © McGraw-Hill Education.  Viruses in the Biological Spectrum (1 of 4) There is no universal agreement on how and when viruses originated Viruses are considered the most abundant microbes on earth Viruses played a role in the evolution of Bacteria, Archaea, and Eukarya Viruses are obligate(THEY NEED A CELL TO LIVE IN) because they can’t do anything by themselves. When they take over a cell, they do harm!!!. They ARE ALSO intracellular parasites 6-3 © McGraw-Hill Education.  Viruses in the Biological Spectrum (2 of 4) TABLE 6.1 Properties of Viruses Obligate intracellular parasites of bacteria, protozoa, fungi, algae, plants, and animals Ultramicroscopic size, ranging from 20 nanometer up to 450 nm (diameter) Not cellular in nature; structure is very compact and economical (just DNA or RNA covered by a protein). Do not independently fulfill the characteristics of life 6-4 © McGraw-Hill Education.  Viruses in the Biological Spectrum (3 of 4) Inactive macromolecules outside the host cell and active only inside host cells (they can’t do anything outside the host. They become active when they affect the host INSIDE not outside). It is EITHER DNA OR RNA BUT NOT BOTH. Capsule: piece that surrounds DNA or DNA Basic structure: consists of protein shell (capsid) surrounding nucleic acid core Nucleic acid of the viral genome is either DNA or RNA but not both Nucleic acid can be double-stranded DNA, single-stranded DNA, single-stranded RNA, or double-stranded RNA Molecules on virus surface impart high specificity for attachment to host cell 6-5 © McGraw-Hill Education. Viruses in the Biological Spectrum (4 of 4) Multiply by taking control of host cell's genetic material and regulating the synthesis and assembly of new viruses Lack enzymes for most metabolic processes Lack machinery for synthesizing proteins Take control of host cell’s genetics cell creates more and more viruses. 6-6 © McGraw-Hill Education.  General Size of Viruses (1 of 2) Ultramicroscopic – most