Microbio Ch 13 Q 69-end

What can and cannot destroy prions?

Prions cannot be destroyed by boiling, alcohol, acid, standard autoclaving methods, or radiation.

What is transformation?

Tumor cells undergo transformation; that is, they acquire properties that are distinct from the properties of uninfected cells or from infected cells that do not form tumors.

What are prions?

is a small infectious particle composed of abnormally folded protein that causes progressive neurodegenerative conditions. These mis-folded proteins do not multiply in the host organism that they infect.

What is the pathway of multiplication and inheritance for Retroviridae?

1) Retrovirus enters by fusion between attachment spikes and the host cell receptors. 2) Uncoating releases the two viral RNA genomes and the viral enymes reverse transcriptase, integrate, and protease. 3) Reverse transcriptase copies viral RNA to produce double-stranded DNA. 4) The new viral DNA is transported into the host cell's nucleus, where it is integrated into a host cell chromosome as a provirus by viral integrate. The provirus may be replicated when the host cell replicates. 5) Transcription of the provirus may also occur, producing RNA for new retrovirus genomes and RNA that encodes the retrovirus capsid, enzymes, and envelop proteins 6) Viral proteins are processed by viral protease; some of the viral proteins are moved to the host plasma membrane. 7) Mature retrovirus leaves the host cell, acquiring an envelope and attachment spikes as it buds out.

What is a persistent infection? Why are they important?

A persistent or chronic viral infection occurs gradually over a long period. Typically, persistent viral infections are fatal. A number of persistent viral infections have in fact been shown to be caused by conventional viruses. For example, several years after causing measles, the measles virus can be responsible for a rare form of encephalitis called subacute scle- rosing panencephalitis (SSPE). A persistent viral infection is ap- parently different from a latent viral infection in that, in most persistent viral infections, detectable infectious virus gradually builds up over a long period, rather than appearing suddenly (Figure 13.21).

Give three examples of DNA oncoviruses.

Adenoviridae, Herpes- viridae, Poxviridae, Papovaviridae, and Hepadnaviridae. -HPV, cervical cancer, HBV

What is T antigen? Where can it be found? From where does it come?

After being transformed by viruses, many tumor cells contain a virus- specific antigen on their cell surface, called tumor-specific transplantation antigen (TSTA), or an antigen in their nu- cleus, called the T antigen. Transformed cells tend to be less round than normal cells, and they tend to exhibit certain chro- mosomal abnormalities, such as unusual numbers of chromo- somes and fragmented chromosomes.

What are some examples of latent infections.

All of the human herpesviruses can remain in host cells through- out the life of an individual. When herpesviruses are reactivated by immunosuppression (for example, AIDS), the resulting infec- tion may be fatal.

What cancer does EBV cause?

Bone marrow cancer/ bone

What are oncogenes?

Cancer-causing alterations to cellar DNA affects part of the genome.

What are the methods of entry used by enveloped viruses?

Following attachment, entry occurs. Many viruses enter into eukaryotic cells by receptor-mediated endocytosis (Chapter 4, page 100). A cell's plasma membrane continuously folds inward to form vesicles. These vesicles contain elements that originate outside the cell and are brought into the interior of the cell to be digested. If a virion attaches to the plasma membrane of a po- tential host cell, the host cell will enfold the virion into a fold of plasma membrane, forming a vesicle (Figure 13.14a). Enveloped viruses can enter by an alternative method called fusion, in which the viral envelope fuses with the plasma membrane and releases the capsid into the cell's cytoplasm. For example, HIV penetrates cells by this method (Figure 13.14b).

What are some examples of persistent infections?

For example, several years after causing measles, the measles virus can be responsible for a rare form of encephalitis called subacute scle- rosing panencephalitis (SSPE).

Describe biosynthesis/replication of DNA-containing viruses?

Generally, DNA-containing viruses replicate their DNA in the nucleus of the host cell by using viral enzymes, and they synthesize their capsid and other proteins in the cytoplasm by using host cell enzymes. Then the proteins migrate into the nucleus and are joined with the newly synthesized DNA to form visions. These visions are transported along the endoplasmic reticulum to the host cell's membrane for release. Herpesviruses, papovaviruses, adenovirsues, and hepadnaviruses all follow this pattern of biosynthesis. Poxviruses are an exception because all of their components are synthesized in the cytoplasm. 1-2: Following attachment, entry, and uncoating, the viral DNA is released into the nucleus of the host cell. 3: Transcription of a portion of the viral DNA-- the "early" genes-- occurs next. Translation follows. The products of these genes are enzymes that are required for the multiplication of viral DNA. In most DNA viruses, early transcription is carried out with the host's transcriptase (RNA polymerase); poxviruses, however, contain their own transcriptase. 4: Sometime after the initiation of DNA replication, transcription and translation of the remaining "late" viral genes occur. Late proteins include capsid and other structural proteins. 5: This leads to the synthesis of capsid proteins, which occurs in the cytoplasm of the host cell. 6: After the capsid proteins migrate into the nucleus of the host cell, maturation occurs; the viral DNA and capsid proteins assemble to form complete viruses. 7: Complete viruses are then released from the host cell.

What is a latent infection? Compare it to an acute infection or a persistent infect.

Is the ability of a pathogenic virus to lie dormant (latent) within a cell, denoted as the lysogenic part of the viral life cycle. A persistent or chronic viral infection occurs gradually over a long period. Typically, persistent viral infections are fatal. persistent viral infection is ap- parently different from a latent viral infection in that, in most persistent viral infections, detectable infectious virus gradually builds up over a long period, rather than appearing suddenly

What cancer does HBV cause?

Liver cancer.

Compare biosynthesis/replication of DNA & RNA viruses. What type of viral nucleic acid is associated with special features of biosynthesis.

Look at table 13.4 in the book. Pg. 388.

What are examples of diseases cause by prions?

Mad cow disease

What is the sense strand and antisense strand for RNA?

The RNA within the virion is called a sense strand (or + strand), because it can act as mRNA. After attachment, penetration, and uncoating are completed, the single- stranded viral RNA (Figure 13.17a) is translated into two principal proteins, which inhibit the host cell's synthesis of RNA and protein and which form an enzyme called RNA-dependent RNA polymerase. This enzyme catalyzes the synthesis of another strand of RNA, which is complementary in base sequence to the original infecting strand. This new strand, called an antisense strand (or − strand), serves as a template to produce additional + strands. The + strands may serve as mRNA for the translation of capsid proteins, may be- come incorporated into capsid proteins to form a new virus, or may serve as a template for continued RNA multiplication. Once viral RNA and viral protein are synthesized, maturation occurs.

How could retroviruses cause cancer?

The ability of retroviruses to induce tumors is related to their production of a reverse transcriptase by the mechanism described earlier (see Figure 13.19). The provirus, which is the double-stranded DNA molecule synthesized from the viral RNA, becomes integrated into the host cell's DNA; new genetic material is thereby introduced into the host's genome, and this is the key reason retroviruses can contribute to cancer. Some retroviruses contain oncogenes; others contain promoters that turn on oncogenes or other cancer-causing factors.

What are the possible methods of maturation and release of animal viruses? Do they always result in death?

The first step in viral maturation is the assembly of the protein capsid; this assembly is usually a spontaneous process. The cap- sids of many animal viruses are enclosed by an envelope consist- ing of protein, lipid, and carbohydrate, as noted earlier. Examples of such viruses include orthomyxoviruses and paramyxoviruses.The envelope protein is encoded by the viral genes and is incor- porated into the plasma membrane of the host cell. The envelope lipid and carbohydrate are encoded by host cell genes and are present in the plasma membrane. The envelope actually develops around the capsid by a process called budding (Figure 13.20). After the sequence of attachment, entry, uncoating, and bio- synthesis of viral nucleic acid and protein, the assembled capsid containing nucleic acid pushes through the plasma membrane. As a result, a portion of the plasma membrane, now the enve- lope, adheres to the virus. This extrusion of a virus from a host cell is one method of release. Budding does not immediately kill the host cell, and in some cases the host cell survives. Nonenveloped viruses are released through ruptures in the host cell plasma membrane. In contrast to budding, this type of Viral capsid Host cell plasma membrane release usually results in the death of the host cell.

Name a human RNA virus that causes cancer.

The human T-cell leukemia viruses (HTLV-1 and HTLV-2) are retroviruses that cause adult T-cell leukemia and lymphoma in humans. (T cells are a type of white blood cell involved in the immune response.)

What is a provirus?

The viral DNA is then integrated into a host cell chromosome as a provirus. Unlike a prophage, the provirus never comes out of the chromosome. As a provirus, HIV is protected from the host's immune system and antiviral drugs.Sometimes the provirus simply remains in a latent state and replicates when the DNA of the host cell replicates. In other cases, the provirus is expressed and produces new viruses, which may infect adjacent cells. Mutagens such as gamma radiation can induce expression of a provirus. In oncogenic retroviruses, the provirus can also convert the host cell into a tumor cell; pos- sible mechanisms for this phenomenon will be discussed later.

How were viruses connected to cancer?

The viral cause of cancer can often go unrecognized for sev- eral reasons. First, most of the particles of some viruses infect cells but do not induce cancer. Second, cancer might not de- velop until long after viral infection. Third, cancers do not seem to be contagious, as viral diseases usually are.

Why are RNA-dependent RNA Polymerase sometimes needed?

This enzyme catalyzes the synthesis of another strand of RNA, which is complementary in base sequence to the original infecting strand.

What happens in uncoating? Where does this occur?

Uncoating is the sep- aration of the viral nucleic acid from its protein coat once the virion is enclosed within the vesicle. The capsid is digested when the cell attempts to digest the vesicle's contents, or the nonenvel- oped capsid may be released into the cytoplasm of the host cell. This process varies with the type of virus. Some animal viruses accomplish uncoating by the action of lysosomal enzymes of host cell. These enzymes degrade the proteins of the viral capsid. The uncoating of poxviruses is completed by a specific enzyme encoded by the viral DNA and synthesized soon after infection. For other viruses, uncoating appears to be exclusively caused byenzymes in the host cell cytoplasm. For at least one virus, the po- liovirus, uncoating seems to begin while the virus is still attached to the host cell's plasma membrane.

What is reverse transciptase and why is it needed for some viruses?

Viral enzyme copies viral RNA to make DNA in cytoplasm; DNA moves to nucleus. -reverse transcrip- tase, which uses the viral RNA as a template to produce comple- mentary double-stranded DNA. This enzyme also degrades the original viral RNA. The name retrovirus is derived from the first letters of reverse transcriptase. The viral DNA is then integrated into a host cell chromosome as a provirus.

What cancer does HPV cause?

Virtually all cervical and anal cancers.

What are oncoviruses?

Viruses capable of inducing tumors in animals.

Can prion disease be inherited? transmitted

Yes, yes

What are the pathways of multiplication used for the ssRNA (+ strand), ssRNA (- strand), and dsRNA viruses?

a) After uncoating, single-stranded RNA (ssRNA) viruses with a + strand genome are able to synthesize proteins directly from their + strand. Using the + strand as a template, they transcribe - strands to produce additional + strands to serve as mRNA and be incorporated into capsid proteins as the viral genome. b) The ssRNA viruses with a - strand genome must transcribe a + strand to serve as mRNA before they being synthesizing proteins. The mRNA transcribes addition - strands for incorporation into capsid protein. Bothe ssRNA and c) dsRNA viruses must use mRNA (+ strand) to code for proteins, including capsid proteins.

What happens in attachment for animal viruses?

animal viruses have attachment sites that at- tach to complementary receptor sites on the host cell's surface. How- ever, the receptor sites of animal cells are proteins and glycoproteins of the plasma membrane. Moreover, animal viruses do not possess appendages like the tail fibers of some bacteriophages. The attach- ment sites of animal viruses are distributed over the surface of the virus. The sites themselves vary from one group of viruses to an- other. In adenoviruses, which are icosahedral viruses, the attach- ment sites are small fibers at the corners of the icosahedron (see Figure 13.2b). In many of the enveloped viruses, such as influenza virus, the attachment sites are spikes located on the surface of theenvelope (see Figure 13.3b). As soon as one spike attaches to a host receptor, additional receptor sites on the same cell migrate to the virus. Attachment is completed when many sites are bound. Receptor sites are inherited characteristics of the host. Conse- quently, the receptor for a particular virus can vary from person to person. This could account for the individual differences in suscepti- bility to a particular virus. For example, people who lack the cellular receptor (called P antigen) for parvovirus B19, are naturally resistant to infection and do not get fifth disease (see page 605). Understand- ing the nature of attachment can lead to the development of drugs that prevent viral infections. Monoclonal antibodies (discussed in Chapter 18) that combine with a virus's attachment site or the cell's receptor site may soon be used to treat some viral infections.