Microbiology Chapter 14.txt

• 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

Nucleic acid

Capsomeres

Protein

Viruses that lyse the cell while carrying out the lytic cycle

The virion is taken wholly into the host cell

Smallpox and bacteriophage

Virion

Nucleocapsid

Herpesvirus and poliovirus

Envelope

Capsid

Spikes

• Bacteriophage of the T-even group, T2, T4, T6.
• These are large, complex, naked DNA virions with the characteristic head and tail of bacteriophages.

Attachment

Nucleic acid

Enzymes

20 to 40

Lysozyme

Receptors on the plasma membrane

Phagocytosis

Positive-stranded

Amantadine

Interferon

Attnuated virus

Ultraviolet light

Formaldehyde

Lipshutz bodies

Helix

Bacteriophage

Virulent

Hemagglutination

Acyclovir (herpes) or AZT (HIV)

Inactivated virus

Detergents

Viroids

Prions

• 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.

• 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.

Adapted John Enders, Thomas Weller and Fredrick Robbins test tube medium to produce massive quantities of virus for use in polio vaccines

Diagnosing several bacterial diseases

Replacing nitrogenous bases in DNA

• The host cell during replication.
• It is composed primarily of lipids

Nucleic acid and protein

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
• DNA
• RNA

• capsid
• capsomeres

The protein coat, made up of capsomeres

The capsid with its enclosed genome

Some capsid proteins that help the virus attach to and penetrate the host cell

Only a nucleocapsid

Are enveloped viruses

A completely assembled, infectious virus outside its host cell

What organisms the virus can infect

On capsid structure

Many viruses infect certain cell or tissue types within the host

• Helix
• Icosahedron
• Complex

• Person�s name
• Location found
• After disease

• Six DNA families
• Thirteen RNA families
• One miscellaneous family
• The International Committee on Taxonomy of Viruses (ICTV) is developing a classification system

single- or double-stranded DNA genomes

• single- or double-stranded RNA genomes
• + strand RNA viruses have mRNA genomes
• � strand RNA viruses have RNA strands that would be complementary to mRNA

Indirectly through a DNA intermediate

• Attachment - chance
• Penetration - lysozyme
• Biosynthesis - makes copies
• Maturation - assembly line
• Lysis - release

virulent viruses that carry out a lytic cycle of infection

A few of the genes needed for viral synthesis and replication

Attachment occurs when a phage�s tail fibers match with a receptor site on the bacterium�s cell wall

• Penetration occurs when the phage tail releases lysozyme to dissolve a portion of the cell wall
• Phage DNA is injected into the bacterial cytoplasm

Biosynthesis is the production of new phage genomes and capsid parts

Maturation is the assembly of viral parts into complete virus particles

• 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

• Attachment at cell membrane
• Penetration of whole virus
• Uncoating by lysozymes
• Replication: Biosynthesis and Maturation
• Envelope acquisition

• 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

Intact nucleocapsids

• The separation of the capsid from the genome
• This occurs as some animal viruses enter the cell

• 1 of 2 things after uncoating
• 1: RNA stays in Cytoplasm and maturation and biosynthesis occurs there
• 2: DNA moves into the nucleus.
• 2A: Biosynthesis in the cytoplasm
• i. the envelope comes from the nucleus and release of virus causes death of cell
• 2B: Maturation in nucleus or cytoplasm
• i. the envelope comes from the cell membrane and cell death isn't necessary.

• 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
• Retrovirus
• Can cause transduction

• 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

• To transcribe their RNA to DNA
• It can then be inserted into the host chromosome

Stops viral attachment

• Base analog
• Herpes simplex

• Base analog
• Genital herpes

• Base analog
• HIV

• Mutated bases with nonworking nucleotides
• Makes the virus DNA stop working so replication fails

• Flatwarts
• A heartburn medication

• viral penetration/uncoating
• genome replication
• maturation/release

• inserting base analogs in the replicating DNA strand
• blocking replication of the viral genome

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

• 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

Anti-cancer properties

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

• Cell eating
• The body sees the infected cell and sends white blood cells to eat the infected cell
• Free floating viruses are eaten too

• Inactivated viruses
• Attenuated viruses
• DNA vaccines

• Heat
• UV light

• Formaldehyde
• Metals
• Phenols
• Lipid solvents

• Inoculations to fertilized eggs
• Inoculations of tissue cultures
• Observation with electron microscope

• Inoculate a fertilized egg
• Grow egg for about 4 days
• Look for deformities in the baby chicken

• Search for viral antibodies
• Hemagglutination
• Hemagglutination Inhibition
• Rivers' postulate

• 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

Examine cells for cytopathic effects (CPEs) of viral infection

Electron microscopy

Nuclear granules

Granules in the cytoplasm

• Foamy cytoplasm
• Mononucleosis
• In white blood cells, especially lymphocytes

• Red spots with patchy white centers
• Plaque formation
• Phage infection, clear areas on the bacterial lawn
• A clear zone within the monolayer

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
• Benign
• Encapsulated
• Rapidly growing cells in a capsule

• Malignant
• Tumor cells can break free from the capsule and spread to other tissues of the body (metastasis)

• Dedifferentiation: lose specialization
• Lose contact inhibition: lose ability to stop growing when they come in contact with another cell
• Sometimes metastisizes

• Invade and erode normal tissue
• Use vital nutrients: prevents healing
• Release hormones

• Viruses
• Radiation
• Chemical carcinogens
• Unknown factors

Up to 20 percent of human tumors

60-90% of human cancers

• Monocucleosis and chronic fatigue syndrom
• Burkitt�s lymphoma: a tumor in the jaw

• Cervical cancer
• There is now a vaccine against the 2 most common strains of HPV

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
• Spongiform encephalopathies

• 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

• Regressive evolution hypothesis
• Cellular origins hypothesis
• Independent entities hypothesis

Viruses are degenerate life-forms

Viruses are derived from subcellular components and macromolecules that escaped from cell walls and replicated inside hosts

Viruses coevolved with cellular organisms from a self-replicating molecule present on primitive Earth