Virology, Test #1

Viruses can cause disease in human:

Virus infections can be from benign to lethal

Our immune defense system protects us very well despite constant encounter.

If defense system is weak/compromised, even very benign infections can be deadly

Viruses are responsible for 20% of human cancers.

Viruses are an important part of ecosystem; Viruses infect all major groups of organisms: vertebrates, invertebrates, plants, fungi, and bacteria.

Viruses do cross species barrier constantly (____)
however, none can cross the eukaryotic/prokaryotic boundary.
There are thousands of copies of retroviral DNA in our genome
Every cell in our body contains viral DNA

All viruses follow these three strategies for survival:
---All viral genomes are packaged inside particles that mediate their _____ from host to host
----The viral genome has all the ____ needed for initiating and completing an infectious cycle within a susceptible, permissive cell.
----All successful viruses are able to establish themselves in a host population so that the virus survival is ensured.

Despite diversity, there are two simple facts that are common among all viruses:
1.)All viral genomes are ____ molecular parasites that can only function after they replicate inside a cell
2.) All viruses must make ____ that can be translated by host cell ribosomes: they are all parasites of host protein synthesis machinery

Microbiology Viruses Viruses are unique acellular structures composed of ____ acid enclosed by a protein coat called a ____. Viruses are obligate intracellular parasites which means that they can express their genes and only reproduce ____ a living host cell, since they lack the structures necessary for independent activity and reproduction. While within cells, viruses have some of the attributes as living organisms, such as the ability to _____; but outside cells, viruses are without activity.

Defining characteristics of viruses

A virus is an infectious, obligate intracellular parasite.

The viral genome comprises either DNA or RNA;
Inside a host cell, the viral genome directs the synthesis of many copies of viral components using ____ systems.

New virus particles are formed by de-novo (biochemical pathway) assembly from newly synthesized component within host cell.

The _____ particles (virions) transmit the viral genome into the next host. Inside the new host cell, the viral particles _____ and start a new infectious cycle.

Classifying Viruses
The Classical System

Four characteristics are used in the classification of viruses:
1. Nature of the ____ acid in th evirion (DNA or RNA)
2. Symmetry of the protein shell (____)
3. Presence or absence of a lipid membrane (______)
4. Dimensions of the virion and capsid

The Baltimore Classification All viruses must produce _____ that can be translated by cellular ribosomes.

In this classification system, the unique pathways from various viral genomes to mRNA define specific virus classes on the basis of the nature and polarity of their _____.

This classification is based on the genome type and mechanism of mRNA production.

The Baltimore classification system places viruses into seven groups:
1.) dsDNA viruses
2.) ssDNA viruses (+)sense DNA
3.)dsRNA viruses
4.)ssRNA viruses (+)sense RNA
5.)ssRNA viruses (−)sense RNA
6.)ssRNA-RT viruses (+)sense RNA with DNA intermediate in life-cycle
7.)dsDNA-RT viruses

mRNA is defined as a ____ streand because it contains immediately translatable information. The RNA and DNA complements of (+) strands are designated ____ strands. Knowledge of strand polarity provides virologists with immediate insight into the steps that must take place to initiate replication and expression of the viral genome.

Viral DNA and RNA genomes are structurally diverse:
Linear
Circular
Segmented
Gapped

What information is encoded in a viral genome?
Gene products and regulatory signals required for:
1.) ____ of genome
2.)_____ and packaging of the genome
3.) _____ and timing of the replication cycle
4.) _____ of host defenses

What information is not contained in viral genome?
No genes encoding complete _____ synthesis machinery
No genes encoding ____ of energy metabolism or membrane biosynthesis
No standard telomeres or ____ found in host chromosomes

Viral Stucture

A complete virus particle, known as a virion, consists of nucleic acid surrounded by a protective coat of protein called a _____.These capsids are formed from _____, identical protein subunits called capsomeres. The symmetrical component's purpose is to provide maximal ____ and non-covalent bonding. Viruses can have a lipid "envelope" derived from the host _____ ______.

The association of viral capsid proteins with viral nucleic acid is called a nucleocapsid.

Size of virion: 20-250nm in diameter

Viral Structure: The function of virion proteins

1. Protection of the genome
---via assembly of a stable protective protein _____
---via specific recognition and _____ of the nucleic acid genome
Protection of genome from hostile environment inside and outside of host
Inside host: proteolytic and nucleolytic enzymes,…
Outside host: temperature, pH, radiation,….
2. Delivery of the genome
---Specfic _____ to external receptors of the host cell
----Transmission of specific signals that induce ____ of the genome.
----Induction of fusion with host cell membranes
----Interaction with internal components of the infected cell to direct _____ of the genome to the appropriate site.

Note: Delivery of the genome is possible because structure is not permanently bonded together
Upon infection can be taken apart or loosened to expose or release the genome
The virus particles have metastable structures
To be infectious, the particle must be metastable (long lived)
3. Other interactions with the host
----With Cellular components for transport to intracellular sites of _____.
----With cellular components to ensure an efficient _____ cycle.
----With the host immune system

Viral Structure: The symmetry rule for Virion Proteins

Each subunit has identical bonding contacts with its neighbors; The repeated interaction of chemically complementary surfaces at the subunit interface naturally leads to symmetry arrangements.

The protein coat of viruses have either Helical or Icosahedral symmetry