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test 2 - NATIVE IMMUNITY An Overview of the Bodys Defenses...

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NATIVE IMMUNITY An Overview of the Body’s Defenses - Resistance to most plant and animal pathogens - Resistance due to physiological processes of humans that are incompatible with those of the pathogen (species resistance) o Correct chemical receptors not present on human cells o Temperature and pH may be incompatible with those necessary for the pathogen’s survival - Number of pathogens for which humans don’t have innate resistance can cause disease The Body’s First Line of Defense - Made up of structures, chemicals, and processes that work to prevent pathogens entering the body - Includes the skin and mucous membranes of the respiratory, digestive, urinary, and reproductive systems VIRUSES Characteristics of Viruses - Cause many infections of humans, animals, plants, and bacteria - Cannot carry out any metabolic pathway - Neither grow nor respond to the environment - Cannot reproduce independently - Recruit the cell’s metabolic pathways to increase their numbers - Cause most of the diseases that plague the industrialized world - Virus—miniscule, acellular, infectious agent having one or several pieces of either DNA or RNA - No cytoplasmic membrane, cytosol, organelles (with one exception) - Have extracellular and intracellular state - Extracellular State o Called virion o Protein coat (capsid) surrounding nucleic acid o Nucleic acid and capsid also called nucleocapsid o Some have phospholipid envelope o Outermost layer provides protection and recognition sites for host cells - Intracellular State o Capsid removed o Virus exists as nucleic acid - Genetic Material of Viruses o Show more variety in nature of their genomes than do cells o May be DNA or RNA, but never both o Primary way scientists categorize and classify viruses
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o Can be dsDNA, ssDNA, dsRNA, ssRNA o May be linear and composed of several segments or single and circular o Much smaller than genomes of cells - Hosts of Viruses o Most viruses infect only particular host’s cells Due to affinity of viral surface proteins or glycoproteins for complementary proteins or glycoproteins on host cell surface o May be so specific they only infect particular kind of cell in a particular host o Generalists—infect many kinds of cells in many different hosts - Capsid Morphology o Capsids—protein coats that provide protection for viral nucleic acid and means of attachment to host’s cells o Capsid composed of proteinaceous subunits called capsomeres o Some capsids composed of single type of capsomere; others composed of multiple types - The Viral Envelope o Acquired from host cell during viral replication or release; envelope is portion of membrane system of host o Composed of phospholipid bilayer and proteins; some proteins are virally coded glycoproteins (spikes) o Envelope’s proteins and glycoproteins often play role in host recognition o CHART of VIRUS v. CELLS Viral Replication - Dependent on hosts’ organelles and enzymes to produce new virions - Replication cycle usually results in death and lysis of host cell lytic replication -
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