Microbiology Fundamentals: A Clinical
Approach, 2nd ed. by Cowan Chapter 5
WITH 77 Correct Answers.
Microbiology Fundamentals: A Clinical
Approach, 2nd ed. by Cowan Chapter 5
WITH 77 Correct Answers.
Viruses - ANSWER-- *Viruses infect EVERY type of cell*, including bacteria, algae,
fungi, protozoa, plants, and animals
- Seawater can contain *100 million viruses per milliliter*
- For many years, the cause of viral infections was unknown
-Louis Pasteur postulated that a "living thing" smaller than bacteria caused these
diseases
-He also proposed the term virus, which is Latin for "poison."
-Ivanovski and Beijerinck showed that a disease in tobacco was caused by a virus
(1892)
-Loeffler and Frosch discovered an animal virus causes foot-and-mouth disease in
cattle
Filterable virus - ANSWER-Early researchers found that *when fluids from host
organisms passed through porcelain filters designed to trap bacteria, the filtrate
remained infectious*
*Obligate Intracellular parasites* - ANSWER-Cannot multiply unless they invade a
specific host cell and *instruct its genetic and metabolic machinery to make and release
new viruses*
Are viruses alive? - ANSWER-- Since *viruses are unable to replicate independently
from the host cell*, they are not living things and should be called infectious molecules
- Even though viruses do not exhibit most of the life processes of cells, they can direct
them, and thus are certainly more than inert and lifeless molecules
- *Viruses are better described as active or inactive*
Vital Role of Viruses in Evolution - ANSWER-- Infect cells and influence their genetic
makeup
- Shape the way cells, tissues, bacteria, plants, and animals have evolved
- 10% of the human genome consists of sequences that come from viruses
- 10 - 20% of bacterial DNA contains viral sequences
Classification & Nomenclature - ANSWER-For many years, animal viruses were
classified on the basis of their hosts and the diseases they caused
, Microbiology Fundamentals: A Clinical
Approach, 2nd ed. by Cowan Chapter 5
WITH 77 Correct Answers.
Newer classification systems emphasize the following:
-hosts and diseases they cause
-structure
-chemical composition
-similarities in genetic makeup
International Committee on the Taxonomy of Viruses
-3 orders
-73 families
-283 genera
Size Range of Viruses - ANSWER-Smallest infectious agents
*Smallest viruses: parvoviruses around 20 nm in diameter*
-Fifth disease in humans
*Largest viruses: mimiviruses around 450 nm in length*
-*Megavirus* is the current largest virus
*Most need an electron microscope to visualize*
Viral Components - ANSWER-Capsids, Nucleic Acids, & Envelopes
Viruses bear no resemblance to cells and lack any of the protein-synthesizing
machinery found in cells
Viral structure is composed of regular, repeating subunits that give rise to their
crystalline appearance
*Contain only those parts needed to invade and control a host cell*
-external coating
-core containing one or more nucleic acid strains of DNA or RNA
-sometimes one or two enzymes (integrase in HIV)
Capsid - ANSWER-- *Protein shell* that *surrounds the nucleic acid*
- Nucleocapsid: the capsid together with the nucleic acid
- *Naked viruses consist ONLY of a nucleocapsid* (b/c no envelope)
- *Most prominent feature of viruses*
What are capsids built from? - ANSWER-- *Capsomeres*: identical *protein subunits*
- Capsomeres *spontaneously self-assemble* into the finished capsid
Approach, 2nd ed. by Cowan Chapter 5
WITH 77 Correct Answers.
Microbiology Fundamentals: A Clinical
Approach, 2nd ed. by Cowan Chapter 5
WITH 77 Correct Answers.
Viruses - ANSWER-- *Viruses infect EVERY type of cell*, including bacteria, algae,
fungi, protozoa, plants, and animals
- Seawater can contain *100 million viruses per milliliter*
- For many years, the cause of viral infections was unknown
-Louis Pasteur postulated that a "living thing" smaller than bacteria caused these
diseases
-He also proposed the term virus, which is Latin for "poison."
-Ivanovski and Beijerinck showed that a disease in tobacco was caused by a virus
(1892)
-Loeffler and Frosch discovered an animal virus causes foot-and-mouth disease in
cattle
Filterable virus - ANSWER-Early researchers found that *when fluids from host
organisms passed through porcelain filters designed to trap bacteria, the filtrate
remained infectious*
*Obligate Intracellular parasites* - ANSWER-Cannot multiply unless they invade a
specific host cell and *instruct its genetic and metabolic machinery to make and release
new viruses*
Are viruses alive? - ANSWER-- Since *viruses are unable to replicate independently
from the host cell*, they are not living things and should be called infectious molecules
- Even though viruses do not exhibit most of the life processes of cells, they can direct
them, and thus are certainly more than inert and lifeless molecules
- *Viruses are better described as active or inactive*
Vital Role of Viruses in Evolution - ANSWER-- Infect cells and influence their genetic
makeup
- Shape the way cells, tissues, bacteria, plants, and animals have evolved
- 10% of the human genome consists of sequences that come from viruses
- 10 - 20% of bacterial DNA contains viral sequences
Classification & Nomenclature - ANSWER-For many years, animal viruses were
classified on the basis of their hosts and the diseases they caused
, Microbiology Fundamentals: A Clinical
Approach, 2nd ed. by Cowan Chapter 5
WITH 77 Correct Answers.
Newer classification systems emphasize the following:
-hosts and diseases they cause
-structure
-chemical composition
-similarities in genetic makeup
International Committee on the Taxonomy of Viruses
-3 orders
-73 families
-283 genera
Size Range of Viruses - ANSWER-Smallest infectious agents
*Smallest viruses: parvoviruses around 20 nm in diameter*
-Fifth disease in humans
*Largest viruses: mimiviruses around 450 nm in length*
-*Megavirus* is the current largest virus
*Most need an electron microscope to visualize*
Viral Components - ANSWER-Capsids, Nucleic Acids, & Envelopes
Viruses bear no resemblance to cells and lack any of the protein-synthesizing
machinery found in cells
Viral structure is composed of regular, repeating subunits that give rise to their
crystalline appearance
*Contain only those parts needed to invade and control a host cell*
-external coating
-core containing one or more nucleic acid strains of DNA or RNA
-sometimes one or two enzymes (integrase in HIV)
Capsid - ANSWER-- *Protein shell* that *surrounds the nucleic acid*
- Nucleocapsid: the capsid together with the nucleic acid
- *Naked viruses consist ONLY of a nucleocapsid* (b/c no envelope)
- *Most prominent feature of viruses*
What are capsids built from? - ANSWER-- *Capsomeres*: identical *protein subunits*
- Capsomeres *spontaneously self-assemble* into the finished capsid
