Virus Structure & Antiviral Drug Design

Explain what it means when viruses are described as filterable

when infectious fluids from host organisms are passed through porcelain filters designed to trap bacteria, the filtrate remains infectious

Identify better terms for viruses than alive or dead

active or inactive

Discuss the size of viruses relative to other microorganisms

viruses represent the smallest infectious agents (with some unusual exceptions)

Function of viral capsids

a shell that surrounds the nucleic acid in the central core

Helical capsids

have rod-shaped capsomers that bond together to form a series of hollow discs resembling a bracelet

Icosahedral capsids

a 3-dimensional, 20-sided figure with 12 evenly spaced corners

Complex capsids

may have multiple types of proteins and take shapes that are not symmetrical; they are never enveloped

Distinguish between enveloped and naked viruses

Enveloped: composed of a nucleocapsid surrounded by an envelope; envelope usually has spikes

Naked: simplest virus, consisting of a geometric capsid assembled around a nucleic acid strand or strands

Explain the importance of viral surface proteins, or spikes

spikes are essential for the attachment of viruses to the next host cell

Diagram the possible configurations that nucleic acid viruses may possess

double-stranded DNA

single-stranded DNA

double-stranded RNA

single-stranded RNA

single-stranded RNA reverse transcriptase

Diagram the five-step life cycle of animal viruses

Adsorption

Penetration and Uncoating

Synthesis

Assembly

Release

Define the term cytopathic effect and provide one example

virus-induced damage to the cell that alters its microscopic appearance

ex. the fusion of multiple host cells into single large cells containing multiple nuclei

Discuss both persistent and transforming infections

persistent: can last from a few weeks to the remainder of the host's life

transforming: enter a host cell and permanently alter its genetic material, leading to cancer

Provide thorough descriptions of both lysogenic and lytic bacteriophage infections

lyosgenic: the host chromosome carries bacteriophage DNA

lytic: the host cell becomes so packed with viruses that it lyses-splits open-thereby releasing the mature virions

List the three principal purposes of cultivating viruses

-isolate and identify viruses in clinical specimens

-prepare viruses for vaccines

-do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells

Describe three ways in which viruses are cultivated

-using live animal inoculation

-using bird embryos

-using cell (tissue) culture techniques

Name two noncellular infectious agents besides viruses

prions

viroids

Analyze the relative importance of viruses in human infection and disease

the number of viral infections that occur on a worldwide basis is nearly impossible to measure accurately

Discuss the primary reason that antiviral drugs are more difficult to design than antibacterial drugs

the nature of viruses; it is hard to make medications without severe side effects