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

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

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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