Ch 6 – Viruses
MC
1 C a virus is a tiny infectious particle
2 D viruses are known to infect all organisms
3 D the capsid is composed of protein subunits called capsomers
4 B the envelope of an animal virus comes from the membrane of the host cell
5 D the nucleic acid of a virus is either DNA or RNA
6 A steps of viral multiplication (adsorption, penetration, replication, maturation, release)
7 A prophages are an early stage of the development of a bacterial virus
8 D nucleic acid of animal virus enters cell by (translocation, fusion, endocytosis)
9 B RNA virus multiply in cytoplasm, DNA virus multiply in nucleus
10 B enveloped viruses carry surface receptors called spikes
11 C latent viruses remain in cells and cause recurrent disease
12 D cytopathic effects of viruses include: inclusion bodies, multiple nuclei, giant cells
13 D viruses can’t be cultivated in blood agar (need living cells)
14 A clear patches in cell culture that indicates virus infection are called plaques
15 an enveloped virus is pictured (similar to herpes virus shown on page 166)
CQ
1a
Viruses are between living and non-living
Made of a capsid (protein) and nucleic acid (DNA or RNA)
No metabolism or respiratory enzymes
Reproduce using the cell machinery of infected cell (host)
Genetic parasites
Pass through filters that have very tiny pores (openings)
Ultramicroscopic (need e- microscope to visualize)
Some have envelopes
May have unique nucleic acids (single strand DNA or double strand RNA)
Some viruses may be latent
2a viruses are incapable of reproducing on their own outside of a host cell
4a nucleic acid (DNA or RNA) encased by a protein capsid (protective covering)
4b capsid is a protective protein coat that prevent the nucleic acid from being damaged
4c
5a bacteriophages are viruses that infect bacterial cells,
6a need to use machinery of host cells (ribosomes, enzymes etc.)
7a Most important (DNA or RNA viruses) also – animal, plant, bacteriophage,
enveloped or not
8a
steps in phage lytic cycle
1. adsorption (docking) phage tail recognizes receptors on bacteria (pili, flagella)
2. penetration – inject nucleic acid into cell (syringe like structure through cell
wall)
3. making phage copies (copy DNA and then produce proteins) then phage
viruses are assembled inside the cell
4. Lysis – eventually the cell is so packed with viruses that it bursts open
In animal cells
1. attachment to cell membrane
2. whole virus is engulfed or surface of virus fuses with cell membrane and
nucleic acid enters
3. some events (DNA pol or RNA pol occur in nucleus) others protein assembly
occur in the cytoplasm (at ribosomes)
10a receptors (usually glycoproteins) on the cell membrane determine if viruses can
dock on cells or not. These types of receptors are often species specific, which means
that a virus that infects one species probably can’t infect a different species if that second
species receptor proteins are significantly different.
12a Cells hold the virus, but are not lysed right away. This latent infections may cause
cellular damage or they may lead to the development of cancer.
12b Genetic material of an oncogenic virus becomes incorporated into chromosomes of
the host organism. This type of infection can lead to cancer because insertion of viral
DNA happens in random locations in the host organism’s chromosome. The insertion
may occur in a harmless location or it might take place in a location where the function of
an important gene is disrupted.
14a Prions are believed to cause both Creutzfeldt-Jakob disease and mad cow (bovine
spongiform encephalopathy) as prions (naturally occurring in the brain) 3-D
conformation changes, the disease process is triggered
14b Prions consist only of proteins. Unlike viruses, they contain no nucleic acids
(genetic material). It is not fully understood exactly how prions cause disease. One
hypothesis is that the proteins that cause prion related disease (Creutzfeldt Jakob in
humans) occur naturally in the brain and are caused to change shape, and therefore
function, when the body is exposed to altered prions (eating beef from cows with mad
cow disease). This hypothesis is supported by knowledge of families who show
hereditary Creutzfeldt Jakob disease. Their prion proteins most likely contain a mutation
which makes them much more likely to alter the prion protein shape and cause disease.
15 Because viruses are so much simpler than bacteria (contain only nucleic acid and
protein) they are much more difficult to combat. Most chemotherapeutic agents that
impact viral nucleic acids and proteins will very likely also impact host cell nucleic acids
and proteins
CT
10a Viruses are difficult to kill because technically speaking they were never alive.
Most research involves attempts to find ways to block its ability to reproduce. Drugs
may be developed to combat viruses using the following types of techniques.
-
Block the virus from being able to adhere to the cell.
Block the virus from being able to gain entry into the cell.
Inhibit the activity of virus specific enzymes (reverse transcriptase
inhibitors are an example of this type of drug activity)
Find ways to stop new virus particles from being assembled after virus
proteins have been produced and nucleic acids have been replicated.