Microbiology Chapter 14.txt
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Microbiology Chapter 14.txt
Microbiology Chapter 14
A twenty-sided shape. It has 20 triangular faces and 12 corners.
Herpesvirus and poliovirus have this shape.
The viral genome of almost all viruses contains either DNA or RNA but not both and the nucleic acid occurs in either a double or single stranded form.
The nucleic acid is usually a circular or linear molecule.
The genome is folded or coiled to make it smaller
The protein coat of a virus particle.
Gives shape and symmetry to the virus.
The capsid is generally subdivided into individual protein subunits.
The organization of capsomeres yields the viral symmetry.
A completely assembled and infectious virus outside its host cell
A virus that infects a bacteria.
They can destroy the cells they infect
Phage = eat
Identified by Felix d'Herrelle
The phage DNA integrates into the bacterial chromosome as a prophage.
The bacterial cell survives the infection and continues to grow and divide normally.
The prophage is copied into daughter cells during binary fission.
One way a bacteriophage can replicate itself
The number of virions released per infected cell
A provirus is formed when a virus integrates its DNA into a *eukaryotic* host cell and then is present in every division of the cell. This is a stable association.
A noticeable deterioration or structural change to the host cell when infected by a virus.
Assists in clinical laboratory diagnosis with a light microsope
A substance facilitating the attachment and penetration of influenza viruses into host cells
A clear zone in the cloudy lawn of bacterial cells or monolayer of animal cells when culturing a virus.
A base analog that resembles DNA bases and is a useful antiviral agent in diseases caused by DNA viruses such as herpes.
Interferon (IFN) is a group of naturally-produced proteins that alert cells to a viral infection.
Some IFNs have anti-cancer properties.
A weakened virus
A cell escapes the cell's cycle controlling factors and as it continues to multiply, a cluster of cells soon forms.
The cluster eventually yields a clone of abnormal cells referred to as a tumor.
Chemical and physical agents that produce cellular changes leading to cancer.
Genes capable of transforming a cell when activated.
Tiny fragments of nucleic acid known to cause diseases in crop plants.
An infectious protein lacking nucleic acid.
Cytoplasmic nucleoprotein inclusions found in the brain tissue of a rabid animal.
Two of the major shapes of viruses are
Helix and icosahedron
The genome of a virus consists of
A viral capsid is divided in subunits called
The organic compound of which a capsid is composed of is
Viruses that lyse the cell while carrying out the lytic cycle
The virion is taken wholly into the host cell
Two viruses with a complex shape are
Smallpox and bacteriophage
A complete virus outside its host cell is called a
The genome plus the capsid of a virus is its
Two examples of diseases caused by icosahedral viruses are
Herpesvirus and poliovirus
The name given to the flexible membrane at the outer surface of some viruses is
The portion of an unenveloped virus that stimulates the immune system of the body is the
Functional projections of a viral envelope are referred to as
Virus replication has been most thoroughly studied in bacterial viruses known as
Bacteriophage of the T-even group, T2, T4, T6.
These are large, complex, naked DNA virions with the characteristic head and tail of bacteriophages.
The first stage of replication is _____, a process that involves specificity between bacterium and phage.
In order for a virus to replicate, its ____ must be set free in the host cell cytoplasm.
During biosynthesis, the host cell produces ____ for manufacturing viral parts
The burst time for bactgeriophages averages from ___ to ___ minutes
20 to 40
The release stage of phage replication is facilitated by the enzyme
For animal viruses, the viral absorption site exists on the host's
Receptors on the plasma membrane
Penetration also is different for animal viruses with fusion and ___ used as important methods of entry into the host cell cytoplasm
For some animal viruses, the nucleic acid is a ____ RNA, which acts like a messenger RNA molecule
Used for treatment of influenza
Alpha, beta, and gamma preins that inhibit viral replication
Viruses that replicate at a very low rate
Stimulates ajacent thymine bases to bind together
Reacts with free amino groups on viral nucleotides to prevent replication
Cellular granules associated with herpes simplex virus
Tightly wound coil resembling a spring
A bacterial virus
A phage that lyses the host cell
Viral clumping of red blood cells
A type of base analog for treating viruses
Acyclovir (herpes) or AZT (HIV)
Viruses that cannot replicate following chemical or physical treatment
Chemicals that dissolve the lipd in the viral envolope
Particles containing fragments of nucleic acid but no protein
Infectious protein particles apparently without nucleic acid
Resembles thymine and during virus replication could be used when thymine should be present.
They insert themselves into the replicating DNA strand and block the ability of the virus to continue replicating its genome.
John Enders, Thomas Weller, Fredrick Robbins
Worked for Children's Hospital of Boston
Developed a test tube medium of nutrients, salts, and pH buffers in which living animal cells could remain alive.
Polio cells could replicate in the living cells in huge numbers.
Jonas Salk and Albert Sabin
Adapted John Enders, Thomas Weller and Fredrick Robbins test tube medium to produce massive quantities of virus for use in polio vaccines
Phage typing is useful for
Diagnosing several bacterial diseases
Base analogs prevent viral replication by
Replacing nitrogenous bases in DNA
Where is the envelope obtained from?
The host cell during replication.
It is composed primarily of lipids
A virus is a biological particle composed of
Nucleic acid and protein
All viruses have
A genome and a capsid
Small, obligate intracellular parasites
They lack the machinery for generating energy and large molecules
They need a host eukaryote or prokaryote to replicate
The viral genome contains either DNA or RNA, but not both
Nucleic acid core = genome
The capsid is
The protein coat, made up of capsomeres
The nucleocapsid is
The capsid with its enclosed genome
Some capsid proteins that help the virus attach to and penetrate the host cell
Naked viruses are composed of
Only a nucleocapsid
Viruses surrounded by an envelope
Are enveloped viruses
A virion is
A completely assembled, infectious virus outside its host cell
A host range refers to
What organisms the virus can infect
Host range depends
On capsid structure
Many viruses infect certain cell or tissue types within the host
Viruses occur in various shapes
Classification by family
Six DNA families
Thirteen RNA families
One miscellaneous family
The International Committee on Taxonomy of Viruses (ICTV) is developing a classification system
DNA viruses contain
single- or double-stranded DNA genomes
RNA viruses contain
single- or double-stranded RNA genomes
+ strand RNA viruses have mRNA genomes
� strand RNA viruses have RNA strands that would be complementary to mRNA
Retroviruses are replicated
Indirectly through a DNA intermediate
The Replication of Bacteriophages Is a Five-Step Process
Attachment - chance
Penetration - lysozyme
Biosynthesis - makes copies
Maturation - assembly line
Lysis - release
T-even group bacteriophages are
virulent viruses that carry out a lytic cycle of infection
The phage nucleic acid contains only
A few of the genes needed for viral synthesis and replication
Bacteriophage replication Phase 1
Attachment occurs when a phage�s tail fibers match with a receptor site on the bacterium�s cell wall
Bacteriophage replication Phase 2
Penetration occurs when the phage tail releases lysozyme to dissolve a portion of the cell wall
Phage DNA is injected into the bacterial cytoplasm
Bacteriophage replication Phase 3
Biosynthesis is the production of new phage genomes and capsid parts
Bacteriophage replication Phase 4
Maturation is the assembly of viral parts into complete virus particles
Bacteriophage replication Phase 5
Release is the exit of virions from the bacterium
It is also called the lysis stage when the cell is ruptured
Temperate phages do not lyse the host
They insert their DNA into the bacterial chromosome as a prophage (lysogenic cycle)
Temperate phages do not lyse the host
They insert their DNA into the bacterial chromosome as a prophage
Replication of animal viruses
Attachment at cell membrane
Penetration of whole virus
Uncoating by lysozymes
: Biosynthesis and Maturation
Animal Virus Replication Has Similarities to Phage Replication
Animal viruses attach to host plasma membrane via spikes on the capsid or envelope
Since receptor sites vary from person to person, some people are more susceptible to a certain virus than others
Animal viruses are usually taken into the cytoplasm as
The separation of the capsid from the genome
This occurs as some animal viruses enter the cell
Replication of a DNA Animal Virus
1 of 2 things after uncoating
: RNA stays in Cytoplasm and maturation and biosynthesis occurs there
: DNA moves into the nucleus.
: Biosynthesis in the cytoplasm
i. the envelope comes from the nucleus and release of virus causes death of cell
: Maturation in nucleus or cytoplasm
i. the envelope comes from the cell membrane and cell death isn't necessary.
After the new animal viruses are assembled
Envelope proteins are incorporated into a cellular membrane
The virus buds, taking the membrane part with it as an envelope
The provirus encodes a repressor protein that prevents activation of the viral genes necessary for replication
It is in a state of latency
Can cause transduction
Latent proviruses are
Immune to the host body�s defenses
They are propagated each time the cell�s chromosome is reproduced
Eventually the provirus will be activated and replicate
Retroviruses use reverse transcriptase
To transcribe their RNA to DNA
It can then be inserted into the host chromosome
Stops viral attachment
Mutated bases with nonworking nucleotides
Makes the virus DNA stop working so replication fails
A heartburn medication
Some antivirals exist to affect:
Most antivirals target the replication enzymes of the virus by
inserting base analogs in the replicating DNA strand
blocking replication of the viral genome
Reverse transcriptase inhibitors
Prevent the synthesis of DNA in retroviruses
Impede the HIV protease that trims viral proteins in capsid construction
Block an enzyme in the spike of influenzaviruses
This prevents the release of new virions into the body
Interferon (IFN) is
A group of naturally-produced proteins that alert cells to a viral infection
Only works in humans if it's from humans.
Pig interferon doesn't work
Produced by infected cell to protect nearby cells
Some IFNs have
Cells in an antiviral state can
Inhibit viral replication by preventing protein synthesis
2nd time exposed to a virus, your body knows how to destroy the virus before you get the disease
The body sees the infected cell and sends white blood cells to eat the infected cell
Free floating viruses are eaten too
Viral vaccines are made from
Physical agents to inactivate a virus
Chemical agents to inactivate a virus
Methods of direct detection of viruses
Inoculations to fertilized eggs
Inoculations of tissue cultures
Observation with electron microscope
Using eggs for virus detection
Inoculate a fertilized egg
Grow egg for about 4 days
Look for deformities in the baby chicken
Indirect detection of viruses
Search for viral antibodies
Rivers� postulates expand upon Koch�s postulates to help identify viruses
Filtrates of infectious material shown not to contain bacterial or other cultivatable organisms must produce the disease or its counterpart
Filtrates must produce specific antibodies in appropriate animals
Cytology uses light microscopy to
Examine cells for cytopathic effects (CPEs) of viral infection
Viruses can be observed directly by
Granules in the cytoplasm
In white blood cells, especially lymphocytes
Red spots with patchy white centers
Phage infection, clear areas on the bacterial lawn
A clear zone within the monolayer
Cancer is an
Uncontrolled growth and spread of cells
A tumor is a clone of abnormal cells
The body surrounds a tumor with a capsule of connective tissue
Rapidly growing cells in a capsule
Tumor cells can break free from the capsule and spread to other tissues of the body (metastasis)
Characteristics of cancer cells
: lose specialization
Lose contact inhibition
: lose ability to stop growing when they come in contact with another cell
Damage by cancer
Invade and erode normal tissue
Use vital nutrients
: prevents healing
Causes of cancer
Viruses are responsible for
Up to 20 percent of human tumors
Carcinogens are associated with
60-90% of human cancers
Monocucleosis and chronic fatigue syndrom
: a tumor in the jaw
Human papilloma virus (HPV)
There is now a vaccine against the 2 most common strains of HPV
The oncogene theory
Proto-oncogene: virus enters and interferes, the cell becomes an oncogene
Keeps track of how many times a cell has divided and tells a cell when to stop
If a virus is incorporated into this area it may restart the dividing process or cause uncontrollable growth
Fragments of nucleic acid
Cause plant diseases
Proteinaceous infectious particles
Diseases in humans and animals
13.7 Emerging Viruses and Viral Evolution
Emerging Viruses Usually Arise Through Natural Phenomena
Emerging viruses may spread to new populations, or may expand host range
Can lead to �new� viruses
Mutation can occasionally be advantageous and create a new or new strain of virus
There are three hypotheses for the origin of viruses
Regressive evolution hypothesis
Cellular origins hypothesis
Independent entities hypothesis
The regressive evolution hypothesis
Viruses are degenerate life-forms
The cellular origins hypothesis
Viruses are derived from subcellular components and macromolecules that escaped from cell walls and replicated inside hosts
The independent entities hypothesis:
Viruses coevolved with cellular organisms from a self-replicating molecule present on primitive Earth