Chapter 16 - Biology

what enzyme copies HIV's genetic material, forming DNA?

reverse transcriptase from the virus

HIV infects human T cells

T cells are needed in the immune system. Patients infected with HIV show symptoms that reflect a defective immune response (AIDS).

Viruses cause disease in plants

The color patterns on these plants might look interesting to us, but they're caused by viruses. The pale areas are dead plant cells. Viral infections often spread on the mouths of plant-eating insects.

Viroids can cause diseases

The potato spindle viroid kills plant cells by preventing production of essential plant proteins.

the effects of a virus depend on the

cell types it infects - viruses cause disease by killing infected cells and by stimulating immune responses

what is not a feature associated with viruses?

cytoplasm

describe the first 5 steps in viral replication

(1) attachment: virus adheres to host cell receptor (2) penetration: virus enters cell (3) synthesis: multiple copies of the viral genome and proteins are produced by the host cell (4) assembly: the viral genetic information is packaged in a protein coat (5) release: new viruses leave the host cell

5 steps of viral replication

1. Attachment 2. Penetration 3. Replication and Synthesis 4. Assembly 5. Release

viral replication (nucleic acids)

1. Virus attaches to host. 2. Virus injects its nucleic acids into the cell. 3. Host transcribes and translates viral DNA as if it were its own.

the host cell produces new viruses

1. Virus attaches to host. 2. Virus injects its nucleic acids into the cell. 3. Host transcribes and translates viral DNA as if it were its own. 4. New viruses assemble.

new viruses are released

1. Virus attaches to host. 2. Virus injects its nucleic acids into the cell. 3. Host transcribes and translates viral DNA as if it were its own. 4. New viruses assemble. 5. Viruses leave the cell.

viral replication

1. Virus attaches to host. 2. Virus injects its nucleic acids into the cell.

HIV drugs can work to

1. keep viruses out of uninfected cells 2. inhibit replication of viral genetic information 3. inhibit viral DNA integration into host DNA 4. inhibit assembly of new viruses inside infected host cells.

To make a vaccine, scientists inoculate host cells with the virus

Scientists inject flu viruses into fertilized chicken eggs which are the host cells. The viruses replicate in the eggs. Harvesting viruses from the eggs provides the raw materials to produce a vaccine.

Prions are infectious protein molecules

A prion (PrP) is a normal membrane protein that can refold to adopt an abnormal three-dimensional shape and cause disease. Contact with an abnormal-shaped prion, can trigger a normal shaped prion to refold into an abnormal shape, and thus become active.

Virus DNA can combine with host DNA

A prophage is the DNA of a lysogenic bacteriophage that is inserted into the host chromosome. The prophage replicates when cells divide.

Vaccines help prevent viral infections

A vaccine contains inactive virus or viral proteins. These molecular components of a virus produce an immune response without causing a disease.

Viruses are genes wrapped in a protein coat

A virus is a small, infectious agent made of nucleic acid and protein.

bacteriophage

A virus that infects bacteria - complex structures

describe how HIV replicates in host cells

After attachment and penetration, HIV's reverse transcriptase enzyme copies the viral RNA to DNA. The viral DNA then inserts itself into the host cell's DNA. New HIV particles are synthesized and assembled inside the host cell and are released by budding. A new virus acquires its envelope from the host cell's membrane as it emerges.

Plants can fight viruses too

Although plants do not have an active immune system, their cells can undergo apoptosis (suicide) when infected. Some plants may prevent viral infections from spreading by degrading viral mRNA.

the mosquito is a

reservoir host, providing a continual source of Zika infection for humans

Antibiotics kill bacteria, not viruses

Antibiotics are drugs that block bacterial proteins from functioning, which prevents bacterial cells from carrying out life's processes.

prophage

DNA of a lysogenic bacteriophage that is inserted into a host cell's chromosome

Viruses might or might not kill host cells

Depending on the condition of the host cell, viruses can shift from a lysogenic infection to the lytic pathway.

Anti-HIV drugs block the replication steps

Drugs can block viral binding to cells, reverse transcription, integration of viral DNA, or viral release. Antiviral "cocktails" are combinations of different drugs that interfere with one virus.

viruses come in many shapes and sizes

Each virus has genetic material inside, surrounded by a protein coat, or capsid.

Anti-HIV drugs slow viral replication

For patients already infected with a virus, vaccines won't be helpful. Antiviral drugs prevent the virus from interacting with the host cell and using it for replication.

Replication of RNA viruses is complex

HIV contains RNA as its genetic material. When HIV does replicate, it requires more steps than a DNA virus requires.

Viral RNA is converted to DNA

HIV must produce a DNA copy of its RNA before incorporating genes into the host's DNA. An enzyme called reverse transcriptase carries out the reaction.

Some viruses might linger for years

HIV often remains latent; it does not immediately induce disease symptoms.

Prions can cause diseases

Prions are responsible for mad cow disease and some cases of Creutzfeldt-Jakob disease in people. It is very difficult to destroy prions. They are unaffected by heat, radiation, and chemicals.

Vaccines jump-start the immune system

Vaccines "teach" the immune system to recognize a virus. If you are exposed to the real virus after being vaccinated, your body will be primed to destroy it before it can infect your cells.

viruses use cells to replicate

Viral genes contain instructions for making viruses. Viruses cannot replicate on their own, though. They can only replicate by infecting host cells.

Viroids are infectious RNA molecules

Viroids are circles of RNA that can infect cells. Viroids do not encode proteins, but they do use host cells to replicate.

viruses can lurk inside cells for years

Viruses following the lysogenic pathway "hide" as they replicate, without damaging the host cell.

viruses can kill cells right away

Viruses following the lytic pathway burst from their host cells soon after infection.

Human papilloma viruses (HPV) cause cancer

Viruses like HPV cause cells to replicate too much, instead of killing the cells. HPV is sexually transmitted, and can infect epithelial and cervical cells. It causes cervical, oral, and anal cancers. HPV infection can be prevented by vaccine, condoms, and abstinence.

Animal viruses can cause illnesses

When virally infected cells begin to die, symptoms will reflect the type of cells that are destroyed. The most virulent viruses cause dire illness or death.

reservoir

a host species that serves as a continual source of viral infection for other species - long-term host that acts as a source of viral infection to other hosts

what type of infection is most similar to a lysogenic infection in bacteria?

a latent infection in animals

how is a lysogenic infection similar to and different from a lytic infection?

a lysogenic infection is similar to a lytic infection in that both begin with the attachment and penetration steps. in a lytic infection, the remaining steps (synthesis, assembly, and release) occur immediately, destroying the host bacterium. in contrast, a lysogenic bacteriophage inserts its DNA into the host chromosome, where it is carried on into daughter cells. eventually an environmental change triggers a switch to the lytic pathway, destroying the infected host cells

virus

a nucleic acid (DNA or RNA) in a capsid

what is a prion?

a protein associated with a latent virus

what determine's a virus's host range?

a virus's host range is determined by the presence of a specific receptor on the host cell

how are viroids and prions different from viruses?

all viruses have genetic information and a protein coat. prions are abnormally shaped proteins with no genetic information

the proteins surrounding each virus are shaped to

bind with proteins on host cells

howdo viruses evolve?

by natural selection. mutations in viral DNA or RNA create genetic variation; some variants are more successful than others at infecting cells and leaving descendants

which of the following characteristics of life does a virus have? a. ribosomes b. evolution c. homeostasis d. growth

evolution

virulent

extremely poisonous

reservoir hosts

help spread viruses to other species

virus nucleic acids take over the

host cell

Viruses infect

host cells

which of the following is the largest? a. HIV b. RNA molecule c. e. coli cell d. human T cell

human T cell

latent infections

in animals, a viral infection in which viral genetic information replicated along with the host genome, but infected cells do not immediately produce new viruses; when the infection is reactivated, infected cells begin producing viruses - HIV - dormant in animal cells - some are associated with cancer

encephalopathies

infections that affect the cortex of the brain

viroids

infectious RNA molecule - naked RNA molecules that infect plant cells

prion

infectious particle composed of protein - can take multiple shapes, at least one of which can cause diseases such as transmissible spongiform encephalopathies

Zika virus

infects human cells and causes birth defects - carried and spread by mosquitoes, without harming the mosquitoes

envelope

layer of phospholipids and proteins surrounding the protein coat of some viruses

each virus has specific targe cells that it can

match up with to infect

viruses infect plant cells and spread via

plasmodesmata

capsid

protein coat of a virus

what are some symptoms of viral infection in plants?

some symptoms include small dead spots, mottled leaves, abnormal growth, or even streaking in some flowers

vaccines

substance that initiates a primary immune response to a pathogen without actually causing a disease - combat viral infections - antibiotics don't work against viruses

what is a lytic infection?

the bacteriophage immediately replicated after infecting a bacterium and then bursts out of the host cell, killing it

what is the best way to avoid prion diseases?

the best way to avoid prion disease is to keep animal brains and spinal cords out of the human food chain and out of medical products

virulence

the degree to which a virus, bacterium, or other pathogen harms its host

Although some viruses are complete after the assembly stage, others are not fully formed until they acquire ______ during the release stage.

the envelope

Which flu symptoms are caused directly by the virus, and which are caused by the human immune response?

the influenza virus kills cells in the respiratory tract, causing cough and sore throat. the immune system attacks the virus with fever and inflammation, which cause body aches

the severity of the symptoms associated with a viral infection is related to

the response of the immune system + the number and types of cells that become infected

what is the source of energy and raw materials for the synthesis of viruses in a host cell?

the source of energy and raw materials is the host cell's ATP and its stores of nucleotides and amino acids

how did researchers gather data about SIV infection in wild primates?

the team gathered ape droppings from several sites in Cameroon. they tested each sample for SIV antibodies and extracted genetic material from the sample. the genetic information revealed the ape species that produced the feces and the type of SIV virus (if any) that infected the ape

lytic infection

type of infection in which a bacteriophage enters a cell, replicates, and causes the host cell to burst (lyse) as it releases the new virus - new viruses are immediately synthesized, assembled, and released

lysogenic infection

type of infection in which the genetic material of a bacteriophage is replicated along with the host cell's chromosome. infected cells do not immediately produce new viruses, but the infection may become lytic at any time. - the virus's nucleic acid replicates along with that of a dividing cell without causing problems

host range

types of cells or organisms a virus can infect - bacteria, plants, and humans

how are viral infections treated and prevented?

viral infections are difficult to treat because the viruses infect living host cells; it is difficult to destroy the virus without also destroying the host cell. a few antiviral drugs do prevent viral replication, but viruses are genetically variable, and new treatments quickly select for resistant varieties. the best weapon for prevention is a vaccine, which builds immunity to a virus before a person is exposed.

how can a person acquire a viral infection?

viral infections can be acquired by inhaling respiratory droplets or ingesting contaminated food and water. some viruses are also transmitted by blood transfusion, sexual contact, or contaminated needles

how do viroids and prions cause disease?

viroids interfere with the production of important proteins. an abnormal prion protein "recruits" normal proteins to refold into the abnormal configuration, triggering a chain reaction that results in cell death

how are viruses similar to and different from cells?

viruses and cells both contain genetic material and proteins. however, viruses are smaller than cells and contain no ribosomes or organelles. moreover, viruses do not have metabolism and they cannot replicate on their own; they must infect a living host cell to replicate

how do viruses enter plant cells and spread within a plant?

viruses often enter plant cells by hitching a ride on the contaminated mouthparts of plant-feeding insects. the viruses spread within the plant via plasmodesmata or in vascular tissue