Viruses Exam 4 Microbiology Flashcards
Virus
genetic element that can multiply only in a living (host) cell
Virus is latin for
poison
Viruses are
the most abundant biological entities on earth
Viruses infect what cells
bacteria, algae, fungi, protozoa, plants, and animals
Viruses needs
host cells for everything
Viruses have
their own nucleic acid genome
Virion
the infectious virus particle, the viral genome surrounded by a protein coat
The cause of viral infections are
Unknown
Louis Pasteur
hypothesized that rabies was caused by a living thing smaller than bacteria
They developed a vaccine for rabies in
1884
Dmitri Ivanovski and Martinus Beijernick showed that
a disease in tobacco (plant virus)
Loeffler and Frosch discovered
The animal virus causing foot and mouth disease in cattle
How did viruses originate
Progressive Hypothesis (genetic material capable of moving within a genome)
Escaped genes (Genetic fragments escaped from cells developed protective coating reenter cells to hijack machinery to reproduce )
Regressive Hypothesis aka Reductive evolution
Reduces the amount of gene that it carries in its genome… Adopts a parasitic lifestyle
Are viruses organisms, are they alive
They are nonliving and noncellular
Outside of the host cell they lack most features of life
What role did viruses play in the evolution of life
Shape the way cells, tissues, bacteria, plants, and animals have evolved
Human genome containing sequences that came from viruses
8%
Bacterial DNA containing viral sequences
10 to 20% od bacterial dna
Obligate intracellular parasites
Cannot multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses
Animal viruses were classified on the basis of
their hosts and the diseases they caused (Old System)
Newer classification systems emphasize the following
Hosts and disease they cause
Structure
Chemical composition
Similarities in genetic makeup
International Committee on the Taxonomy of Viruses:
8 orders and 38 families (another 84 families not yet assigned to any order)
Viruses are obligate intracellular parasites of
bacteria, protozoa, fungi, algae, plants, and animals
Viruses are
ubiquitous in nature and had major impact on development
The size of viruses
Ultramicroscopic , ranging from 20nm up to 1000 nothin much diameter
Structure of viruses
Noncellular , very compact and economical
Nucleic acids can either be
Dna or Rna but not both
Molecules (Spikes)
are on the surface and gives them high specificity for attachment to the host cell
Viruses multiply by
taking control of host cell’s genetic material
Which is NOT a potential origin method of viruses
Pre-life Hypothesis
How much of the human genome consists of viral sequences?
8%
Which of the following is False about viruses
They cannot infect algae
What component are viruses missing?
Ribosomes
Resemblance to cells
IT AINT NO RESEMBLANCE
Viral componet
External coating
Core Containing nucleic acids (DNA or RNA)
Matrix proteins and enzymes (occasionally)
Capsid
the protein shell that surrounds the genome of a virus
Naked
viruses have no other layers
Enveloped
viruses have an outer layer consisting of a phospholipid bilayer (from host cell membrane) and viral proteins
Nucleocapsid
nucleic acid + protein in enveloped viruses
Spikes
can be found on naked or enveloped viruse
Spikes allow
viruses to dock with host cells
Viral capsids
Most prominent feature of viruses
Capsomeres
identical protein subunits.. make up viral capsids
Capsomeres spontaneously
self assemble into the finished capsid
Two primary types of Capsids
Helical
Icosahedral
Complex capsids
are never enveloped.
only found in the viruses that infect bacteria
Enveloped viruses
Take a bit of the cell membrane when they are released from a host cell
Enveloped viruses can bud from
Cell membrane
Nuclear envelope
Endoplasmic reticulum
Viruses with a complex capsid infect what type of organism
Bacteria
The viral envelope is
more flexible than the capsid so enveloped viruses are pleomorphic
Genome
the sum total of the genetic information carried by an organism
Why do viruses have such a small amount of genes
Possess only the genes needed to invade host cells and redirect their activity
Escherichia coli has
4,000 genes
Humans have
21,000 genes
Having a larger genome allows…
cells to carry out the complex metabolic activity necessary for independent life.
Viruses typically posses
nly the genes needed to invade host cells
Double stranded
Linear or circular
RNA VIRUSES can be double stranded but
more often single-stranded
Positive-sense RNA:
ready for immediate translation
Negative-sense RNA:
must be converted before translation can occur
Segmented
individual genes exist on separate pieces of RNA similar to human chromosomes
Retroviruses
carry their own enzymes to convert RNA -> DNA
Multiplication Cycles in Animal Viruses
Viruses are minute parasites that seize control of the synthetic and genetic machinery of cells
Length of replication
cycle varies from 8 hours in polioviruses to 36 hours in herpesviruses
Adsorption
A virus can invade its host cell only through making an exact fit with a specific host molecule
Host range of Adsorption
Hepatitis B: Liver cells of humans
Poliovirus: Intestinal and nerve cells of primates
Rabies: various cells of all mammals
Direct fusion of the viral envelope with the host cell membrane:
Envelope merges directly with the cell membrane
Penetration and Uncoating
The flexible cell membrane of the host is
penetrated by the whole virus or its nucleic acid
Penetration through endocytosis
when a entire virus is engulfed by the cell and enclosed in a vacuole or vesicle
SYnthesis- DNA viruses
Enter the host cell’s nucleus and are replicated and assembled there
Synthesis- RNA Viruses
Replicated and assembled in the cytoplasm
Synthesis- Retroviruses turn their
RNA genomes into DNA
Assembly
virus is put together using “parts” manufactured during the synthesis process
Release
the number of viruses released by infected cells is variable, controlled by:
Size of virus
Health of the host cells
Virions released by infected cells vary
Poxvirus infected cell: 3,000 to 4,000
Provirus infected cells: 100,000 virions
Immense Potential for rapid
Carrier relationships
cell harbors the virus and is not immediately lysed
Can remain latent in cytoplasm
Provirus
Viral DNA incorporated into the DNA of the host
E.g. Measles virus. HIV.
Chronic latent state:
Periodically become activated under the influence of various stimuli
Ex. Herpes
Transformed cells
Increased rate of growth
Changes in their chromosomes
Changes in cell’s surface molecules
Capacity to divide indefinitely
Oncoviruses: mammalian viruses capable of initiating tumors
Papillomaviruses
Herpesviruses
Hepatitis B virus
General phases of the animal viral replication cycle EXCEPT: Adhesion
Penetration
Uncoating
Synthesis
Assembly
Release
Adhesion
During which phase of the animal viral replication cycle do we see nucleic acid replication and protein production
Synthesis
Bacteriophage “bacteria eating”
Contain double stranded DNA, some contain rna at times
Bacteriophage “bacteria eating”
Contain double stranded DNA, some contain rna at times
Bacteria that bacteriophages infect
More often pathogenic for humans
Every bacterial species is parasitized by…
various specific bacteriophages
T-even Bacteriophage
Most studied
T Even bacteriophage infects
Escherichia coli
Lysogeny
a condition in which the host chromosome carries bacteriophage DNA
Temperate phages do
Undergo absorption and penetration
Temperate phages do not
undergo replication or release
Viral DNA enters an inactive prophage state:
Inserted into bacterial chromosome -> Copied during normal bacterial cell division
Viral DNA enters an inactive prophage state:
Inserted into bacterial chromosome -> Copied during normal bacterial cell division
Viral DNA enters an inactive prophage state:
Inserted into bacterial chromosome -> Copied during normal bacterial cell division
Induction : Lysogeny
prophage in a lysogenic cell becomes activated and progresses directly into viral replication and the lytic cycle
The Role of Lysogeny in Human Disease
phage genes in the bacterial chromosome can cause the production of toxins or enzymes that the bacterium would not otherwise have
Lysogenic conversion
when a bacterium acquires a new trait from its temperate phage
corynebacterium diphtheriae - lysogenic temperate phage
diphtheria toxin
When phage nucleic acid is incorporated into the nucleic acid of its host cell and is replicated when the host DNA is replicated, this is considered part of which cycle?
lysogenic phase
A virus that undergoes lysogeny is a/an _________.
Temperate phage
Which of the following is incorrect about prophages?
Cause lysis of host cells
