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MCB 2340 microbiology module 2 notes, Best review Document, Rasmussen College
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Microbes: The Invisible RealmProkaryotes and eukaryotes are two types of cells that are very different but share certain
properties such as methods of reproduction, protein synthesis, an organized metabolism,
response to stimuli, and plasma membranes. However, there is one significant difference:
*prokaryotes are without a cell nucleus
*eukaryotes are cells with a membrane bound nucleus
Eukaryotic microorganisms tend to be grouped together by biochemical, metabolic and genetic
characteristics. Most are not pathogenic to humans and animals. Viruses, bacteria and
eukaryotic microorganisms such as fungi, algae, protozoans, slime molds and helminths
(commonly known as worms) are considered significant aspects of human pathogens but not
all of them are pathogenic. In fact, only a small minority of microbes have been implicated with
causing harm to other living organisms (Cowan, 2019).
Each of these types of organisms presents a problem to humans because they impact the health
and well-being of the infected individual. Traditional medicine can treat many of these
infections, but people in developing countries are at risk due to poor socioeconomic
environments, contaminated water supplies, and little or no access to medical care.
What types of relationships happen between organisms?
Symbiosis-two organism live together in a close partnership. The members are called
symbionts.
Three main types of symbiosis occur:
*Mutualism-organisms live in an obligatory but mutually beneficial relationship. (bacteria in
human intestines)
*Commensal-the commensal organism benefits while the host neither benefits or is harmed.
(remora fish on sea turtle)
*Parasitism-the parasitic organism benefits while the host is harmed. (deer tick on humans)
Viruses-what do we know?
Viruses contain either DNA or RNA and are interesting in that they can infect bacteria, plants,
and animals. They are described as acellular and are best described as infectious particles
(rather than organisms) and as either active or inactive (rather than alive or dead) (Cowan 2018).
A virus needs a host in order to replicate and uses host cells as a factory to produce and
assemble components needed to build more virions which are then released and infect mmore
,host cells. Stopping the viral spread is difficult due to the protective layer of the viral coat which
is why antibiotics have no effect on viral infections.
Subviral agents such as viroids, virusoids and prions also exist but tend to be smaller than a
virus with some of the viral properties. Prions are the only one of these three that is a significant
threat to human health.
What are Viruses?
*are not living cells!
*are microscopic particles that infect cells
*are classified using their capsid shape and nucleic acid contents
*genome is either DNA or RNA but never both
*cannot reproduce on their own
*obligate intracellular parasites
*reproduce by hijacking the synthetic and genetic machinery of the host cell
*the host cell may not be damaged upon the virus exiting the host cell
*infections may be acute or persistent
*a persistent infection can last from a few weeks to the reminder of the host’s life.
The virus can incorporate into the DNA of the host, this is called a provirus
*Roseola virus can be passed down from parent to infant in the provirus state
*Measles virus may remain hidden in the brain cells for many years, causing
progressive damage and loss of function.
*Chronic latent state infections can remain over long periods of time and later emerge to
cause recurrent symptoms
*Herpes simplex virus
*Herpes zoster virus
*infect both eukaryotes and prokaryotes
*Bacteriophage (virus): infects bacteria
, Classification of Viruses by Morphology
The International Committee on Taxonomy of Viruses (ICTV) uses viral morphology
(shapes) as part of the virus classification process. These viral shapes are listed below.
Helical Viruses
*Capsids with rod-shaped capsomeres
*Genetic material can be single-stranded RNA (ssRNA) or single-stranded DNA
(ssDNA).
*can be naked (e.g. tobacco mosaic virus) or enveloped (e.g. influenza virus)
Icosahedral viruses
*the icosahedron is a three-dimensional, geometric figure with 12 corners, 20 triangular
faces, and 30 edges.
*arrangement of capsomers varies between the viruses
*examples include Herpesviridae (herpes simplex type 1 virus), Adenoviridae
(adenoviruses), Papovaviridae (human papillomavirus), Parvoiridae (parvovirus
B19)
Enveloped viruses
*range from spherical to filamentous in shape
*viral envelope surrounds the nucleocapsid
*the viral envelope is obtained by budding through a host membrane (usually plasma,
endoplasmic reticulum or nuclear membrane)
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