Bio 61 Exam 3 (ch 18, 19, 20, 40, 41, 47)

Vaccine

A harmless variant or derivative of pathogen that stimulates the immune system to mount defenses against the harmful pathogen.

What does the Host range mean and what is the implication for the spread of viruses?

A limited number of host cells it can infect. A viral infection begins when virus binds to host cell and viral genome makes its way inside. Endocytosis, fusion of viral envelope are ways it can be taken up.

Lytic cycle

A phage replicative cycle that culminates in death of the host cell.

Viroids

A plant pathogen consisting of a molecule of naked, circular RNA a few hundred nucleotides long.

Obligate intracellular parasites

All viruses can only reproduce within the host cell.

What are the components of a virus?

All viruses contain the following two components: 1) a nucleic acid genome and 2) a protein coat/ capsid that covers the genome. Together this is called the nucleocapsid. In addition, many animal viruses contain a 3) membranous/lipid envelope. The entire intact virus is called the virion.

How do all 3 RNA viruses differ in their transmission and transcription/translation strategies?

All viruses that use RNA genome as a template for mRNA transcription require RNA for RNA synthesis. Also use a viral enzyme capable of carrying out this process.

How could you tell apart a virus with an envelope and a virus without an envelope?

An envelope is made up of glycoproteins or plasma membrane. These may help viruses avoid the immune system. They help identify and bind to receptor sites of the host's membrane. They also possess great adaptability.

What might cause a temperate phage to switch to the lytic cycle?

An environmental signal (chemical or high-energy radiation) can trigger the virus genome to exit the bacterial chromosome and switch to the lytic cycle.

Prion

An infectious agent that is a misfolded version of a normal protein. Appear to increase in number by converting correctly folded versions of the protein to more prions.

Virus

An infectious particle incapable of replicating outside of a cell, consisting of an RNA or DNA genome surrounded by a protein coat (capsid) and, for some viruses, a membranous envelope.

What attributes of a virus are also attributes of a living organism? What does it lack?

Bacteria are single-celled, prokaryotic microorgansims that exist in abundance in both living hosts and other areas; they are either good or bad for our health; alive. A virus has no cell structure (acellular) and requires living in a host cell to survive; it causes illness; nonliving.

Different types of viral structures:

Bacteriophage- DNA capsid head/tail. TMV- RNA capsid. Adenoviruses- pink eye, diarrhea, respiratory infections; DNA capsid with glycoproteins. Influenza- RNA capsid, lipid membrane envelope, glycoproteins.

What is the implication for the long incubation time of HIV to cause AIDS?

Combinations of drugs such as nucleosidase reverse transcriptase inhibitors and protease inhibitors can help control viral replication, restore immune function and maintain health.

Viral envelope

Derived from cell membrane of host. Can incorporate viral glycoproteins. Mediate interaction between host cells and virus.

What are the 3 types of RNA viruses?

Double stranded RNA (III); Positive-sense single stranded RNA (IV): can directly serve as mRNA and thus be translated into viral protein immediately after infection...have their genome directly utilized as if it were mRNA, with host ribosomes translating it into a single protein needed for replication; Negative-sense single stranded RNA (V): RNA genome serves instead as a template for mRNA syntheesis. The RNA genome is transcribed into complementary RNA strands, which function as both mRNA and as templates for synthesis of additional copies of genomic RNA. must have their genome copied by an RNA replicase to form a positive sense RNA.

Pandemic vs Epidemic

Epidemic- widespread outbreak. Pandemic- rapidly spreading global epidemic.

What are the types of coats and genomes that viruses can have?

Genomes: double-stranded DNA, single-stranded DNA, double-stranded RNA, or single-stranded RNA. Genomes are usually organized as a single linear or circular molecule of nucleic acid, sometimes multiple molecules. Coats: Capsid either rod-shaped or helical viruses, polyhedral, or more complex.

Why does HIV specifically affect the immune system function?

HIV is a unique human RNA virus, capable of infecting cells of the immune system, specifically targeting T helper cells (CD4 cells), leading to the eventual death of the cell. CD4 cells are vital players in the regulation of immune responses to invading microorganisms. If intreated, 10billion to 100 billion cells new viruses are produced daily.

What kind of coat and genome does HIV have?

HIV is enveloped and contains two identical molecules of single-stranded RNA and two molecules of reverse transcriptase.

Two major routes for transmission.

Horizontal transmission- a plant is infected from an external source of the virus; because the invading virus must get past the outer protective layer (epidermis), a plant becomes more susceptible to viral infections if it has been damaged. Also insects can be carriers of viruses, transmitting disease. Vertical transmission- A plant inherits a viral infection from a parent; occurs in asexual propogation or sexual via infected seeds.

Two different mechanisms for replication:

Lytic cycle- (last stage of infection when the bacterium lyses and releases phages that were produced in cell) a phage replicative cycle that culminates in death of the host cell. Lysogenic cycle-

How has the influenza virus changed over time?

Mutations- New strains of influenza virus genetically different enough from earlier strains that people have little immunity to.

What are some of bacteria's defenses against phages?

NAtural selection- favors mutants with surface proteins that are no longer recognized as receptors by a particular type of phage. Cellular enzymes- restriction enzymes; when the DNA is identified as foreign and cut up by enzymes. *restriction enzy,es and cellular receptor arms races.

Why do viruses evolve quickly?

Natural selection

Properties of life shared by prokaryotic cells, eukaryotic cells, and viruses

Nucleic acids used to store hereditary information, order and complexity in arrangement of biological molecules, and the capacity to evolve.

What are some candidate molecules for the origination of viruses?

Plasmids in bacteria and yeasts and transposons (small mobile DNA segments). All mobile genetic elements.

What is the difference between a prophage and a provirus?

Prophage- a phage genome that has been inserted into a specific site on a bacterial chromosome. Provirus- a viral genome that is permanently inserted into a host genome.

Why is the immune system so detrimental?

Since the viral replication of HIV leads to a progressive loss of CD4 cells, and destruction of CD4 cells renders a patient vulnerable to unusual opportunistic infections, most patients die from AIDS succumb to one or more opportunistic infection.

Retrovirus. retro means backwards.

The RNA animal viruses with the most complicated replicative cycles (Class VI). They are equipped with an enzyme called reverse transcriptase- which transcribes an RNA template into DNA, providing RNA to DNA information flow.

Why are prions so scary?

The act very slowly, with incubation period of 10 years before symptoms develop. This prevents sources of infection from being detected, allowing more infections to occur. Also, virtually indestructible and no cure.

Capsid

The protein shell enclosing the viral genome. Can be rod shaped, polyhedral, or more complex in shape.

Restriction enzymes

Their activity restricts tha ability of the phage to replicate within the bacterium.

Aside from viral infections, what is the main danger of dsDNA viruses?

They are not easy to get rid of. Most of these viruses (herpes) one will have for the rest of life. COpies of the viral DNA can remain behind as minichromosomes in the nuclei of nerve cells; they remain latent until some sort of physical or emitional stress triggers a new round of active virus production.

What is an emergent virus?

Viruses that suddenly become apparent. Three processes: mutation of existing viruses, dissemination of viral disease from small isolated human population, and spread of existing viruses from other animals.

Why does HIV evolve so quickly?

When patients do not adhere to their drug regimen, the virus rapidly eliminates its vulnerability.

Virulent phage

a phage that replicates only by a lytic cycle.

Glycoproteins

proteins with carbohydrates covalently attached.

Capsomeres

the protein subunits that build a capsid.

reverse transcriptase

transcribes an RNA template into DNA, providing an RNA to DNA information flow, the opposite of the usual direction.

bacteriophage

viruses that infect bacteria; first phage studied was E coli. Their capsids have elongated icosahedral heads enclosing their DNA, attached to protein tail.