Viruses

Which of the following is not associated with prions? a. replicating shapes b. mad cow disease c. DNA d. toxic proteins

DNA

Fusion

Method of entry by some enveloped viruses, where the viral envelope fuses with the plasma membrane of the host cell.

Although plant viruses cannot infect humans, what are some of the ways in which they affect humans?

Plant viruses infect crops, causing crop damage and failure, and considerable economic losses.

Why is immunization after being bitten by a rabid animal so effective and why aren't people vaccinated for rabies like dogs and cats are?

Rabies vaccine works after a bite because it takes week for the virus to travel from the site of the bite to the central nervous system, where the most severe symptoms of the disease occur. Adults are not routinely vaccinated for rabies for two reasons: first, because the routine vaccination of domestic animals makes it unlikely that humans will contract rabies from an animal bite; second, if one is bitten by a wild animal or a domestic animal that one cannot confirm has been immunized,there is still time to give the vaccine and avoid the often fatal consequences of the disease.

One of the first and most important targets for drugs to fight infection with HIV (a retrovirus) is the reverse transcriptase enzyme. Why?

Reverse transcriptase is needed to make more HIV-1 viruses, so targeting the reverse transcriptase enzyme may be a way to inhibit the replication of the virus. Importantly, by targeting reverse transcriptase, we do little harm to the host cell, since host cells do not make reverse transcriptase. Thus, we can specifically attack the virus and not the host cell when we use reverse transcriptase inhibitors.

Why can't dogs catch the measles?

The virus can't attach to dog cells, because dog cells do not express the receptors for the virus and/ or there is no cell within the dog that is permissive for viral replication.

How are viroids like viruses?

They both replicate in a cell, and they both contain nucleic acid.

Prions are responsible for variant Creutzfeldt-Jakob Disease, which has resulted in over 100 human deaths in Great Britain during the last 10 years. How do humans obtain this disease?

This prion based disease is transmitted through human consumption of infected meat.

Receptor-Mediated Endocytosis

alternative method of cell penetration used by non-enveloped viruses is for capsid proteins to undergo shape changes after binding to the receptor, creating channels in the host cell membrane. Viral genome is then "injected" into the host cell through these channels in a manner analogous to that used by many bacteriophages.

Gall

appearence of a plant tumor

Which statement is true of viral replication? a. In the process of apoptosis, the cell survives. b. During attachment, the virus attaches at specific sites on the cell surface. c. The viral capsid helps the host cell produce more copies of the viral genome. d. mRNA works outside of the host cell to produce enzymes and proteins.

b. During attachment, the virus attaches at specific sites on the cell surface.

which statement is true? a. A virion contains DNA and RNA. b. Viruses are acellular. c. Viruses replicate outside of the cell. d. Most viruses are easily visualized with a light microscope.

b. viruses are acellular

A bacteriophage can infect ________.

bacteria

Lysis

bursting of a cell

Which statement is true of reverse transcriptase? a. It is a nucleic acid. b. It infects cells. c. It transcribes RNA to make DNA. d. It is a lipid.

c. It transcribes RNA to make DNA.

which of the following statements is false? a. in the lytic cycle, new phage are produced and released into the environment b. in the lysogenic cycle, phage DNA is incorporated into the host genome c .An environmental stressor can cause the phage to initiate the lysogenic cycle. d. Cell lysis only occurs in the lytic cycle.

c. an environmental stressor can cause the phage to initiate the lysogenic cycle

Which of the following is NOT used to treat active viral disease? a. vaccines b. antiviral drugs c. antibiotics d. phage therapy

c. antibiotics

The viral ________ plays a role in attaching a virion to the host cell.

capsid and envelope

cell necrosis

cell death

Baltimore Classification Scheme

classification that is based on how messenger RNA (mRNA) is generated in each particular type of virus

viral core

contains the genome or total genetic content of the virus

which of the following statements about virus structure is true? a. all viruses are encased in a viral membrane b. the capsomere is made up of small protein subunits called capsids. c. DNA is the genetic material in all viruses d. glycoproteins help the virus attach to the host cell

d. Glycoproteins help the virus attach to the host cell

Which statement is not true of viral replication? a. A lysogenic cycle kills the host cell. b. There are six basic steps in the viral replication cycle. c. Viral replication does not affect host cell function. d. Newly released virions can infect adjacent cells

d. Newly released virions can infect adjacent cells

Oncogenic virus cores can be_______. a. RNA b. DNA c. neither RNA nor DNA d. either RNA or DNA

d. either RNA or DNA

Reverse Transcriptase

enzyme found in Baltimore groups VI and VII that converts single-stranded RNA into double-stranded DNA.

Self-replicating

evolving alongside the cells they rely on as hosts.

general shapes of viruses

filamentous, isometric (icosahedral), enveloped, and head and tail

how can a plant receive a virus?

for many plant viruses to be transferred from to plant, damage to some of the plants' cells must occur to allow the virus to enter a new host.

viral genomes

genes that encode proteins that the virus cannot get from the host cell.

non-segmented

genome consists of a single segment of genetic material

segments

genomes that have several nucleic acid.

Lytic cycle

if the virions are released by bursting the cell, the virus replicates by means of a ...

Head and Tail virus

infect bacteria and have a head that is similar to the icosahedral virus and a tail shape like filamentous viruses

Filamentous viruses

long and cylindrical (TMV)

vaccines

may be prepared using live viruses, killed viruses, or molecular sub-units of the virus .

budding

method of exit from the cell used in certain animal viruses, where virions leave the cell individually by capturing a piece of the host plasma membrane

Capsid

nucleic acid genome covered by a protective layer of proteins.

Envelope

outer layer made of protein and phospholipid membranes derived from the host cell.

Devolution

proposes to explains the origin of viruses by suggesting that viruses evolved from free-living cells.

Capsomers

protein subunits that the capsid is made of

What are the two ways an animal virus can enter the host cell?

receptor-mediated endocytosis , and fusion

Isometric Viruses

roughly spherical, such as poliovirus or herpesvirus.

Vaccines_______.

stimulate an immune response

Acute Disease

symptoms get increasingly worse for a short period followed by the elimination of the virus from the body by the immune system and eventual recovery from the infection.

intermittent symptoms

symptoms that occur periodically

Influenza virus is packaged in a viral envelope that fuses with the plasma membrane. This way, the virus can exit the host cell without killing it. What advantage does the virus gain by keeping the host cell alive?

the host cell can continue to make new virus particles

Core classification

the type of genetic material (DNA or RNA) and its structure (single- or double-stranded, linear or circular, and segmented or non segmented)

Latency

these viruses can exist in nervous tissue for long periods of time without producing new virions, only to leave latency periodically and cause lesions in the skin where the virus replicates.

Which statement is true of viroids? a. They are single-stranded RNA particles. b. They reproduce only outside of the cell. c. They produce proteins. d. They affect both plants and animals.

they are single-stranded RNA

Lysogenic Cycle

type of virus replication in which the viral genome is incorporated into the genome of the host cell

Viruses_______.

vary in shape

Acellular

viruses are biological entities that do not have a cellular structure. (lacking component of cells such as organelles, ribosomes, and the plasma membrane)

Capsid Classification

viruses can be classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex.

asymptomatic infections

viruses that cause infections with out any symptoms at all in the host

Chronic infections

viruses that causes long term infections

oncogenic viruses

viruses that have the ability to cause cancer. these viruses interfere with the normal regulation of the host host cell cycle either by introducing genes that stimulate unregulated cell growth (oncogenes) or by interfering with the expression of genes that inhibit cell growth.

Bacteriophages

viruses that infect bacteria

Viral Receptors

viruses use some sort of glycoprotein to attach to their host cell via receptors that are found on cell surfaces and have their own physiological functions.

Enveloped virus

viruses with membranes with surrounding capsids. such as animal viruses (HIV)

productive

when infection of a cell by a bacteriophage results in the production of new virions, the infection is said to be...

Horizontal transmission

when plants viruses are transferred between different plants

Prophage

when the phage DNA is incorporated into the host cell genome

Vertical transmission

when viruses are inherited from a plant parent.

Escapist

accounts for viruses having either an RNA or a DNA genome and suggests that viruses originated from RNA and DNA molecules that escaped from a host cell.

The first electron micrograph of a virus (tobacco mosaic virus) was produced in 1939. Before that time, how did scientists know that viruses existed if they could not see them? (Hint: Early scientists called viruses "filterable agents.")

Viruses pass through filters that eliminated all bacteria that were visible in the light microscopes at the time. As the bacteria-free filtrate could still cause infections when given to a healthy organism, this observation demonstrated the existence of very small infectious agents. These agents were later shown to be unrelated to bacteria and were classified as viruses.

Which is true of DNA viruses? a. They use the host cell's machinery to produce new copies of their genome b. They all have envelopes. c. They are the only kind of viruses that can cause cancer. d. They are not important plant pathogens.

a. They use the host cell's machinery to produce new copies of their genome

Hyperplasia

abnormally high cell growth and division