Biology 121: Viruses Powerpoint

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Both bacter and archaea can protect themselves from viral infection with the _____.

CRISPR-Cas system

Particular nuclease proteins interact with the CRISPR REGION; these are called _____.

CRISPR-associated (Cas) proteins

The resulting RNA's are cut into pieces and bound by ____.

Cas proteins

What does CRISPR stand for?

Clustered Regulary Interspaced Short Palindromic Repeats

RNA polymerase transcribes the proviral ______.

DNA into RNA molecuels

Viruses are classified as ____.

DNA viruses or RNA viruses

The ______ is one of several emerging viruses that cause hemorrhagic fever, an often fatal illness.

Ebola virus

When does a cell begin to manufacture viral proteins?

Once a viral genome has entered a cell

______ use reverse transcriptase to copy their RNA genome into DNA.

Retroviruses

_______ are all caused by prions.

Scrapie in sheep, mad cow disease, and Creutzfeldt-Jakob disease in humans

What does tabacco mosaic disease do?

Stunts the growth of tabacco plants and gives their leaves a mosaic coloration.

Viral infections cannot ______.

be treated by antibiotics

There is controversy about whether the largest virus evolved ______.

before or after cells

Capsids are built from protein subunits called:

capsomeres

Every time the host divides, it ______.

copies the phage DNA and passes the copies to daughter cells

Bacteria have their own ____ against phages.

defenses

Viruses do not fit our _____.

definition of living organisms

Some viruses cause infected cells to produce toxins that lead to _______.

disease symptoms

Others have molecular components such as ________.

envelope proteins that are toxic

The virus makes use of host ______.

enzymes, ribosomes, tRNA's, amino acids, ATP, and other molecules

The relationship between phage and bacteria is in constant _____.

evolutionaly flux

It is possible that ______ may allow mosquitoes that carry viruses to expand their range.

global climate change

Many plant viruses have a _______, while others have an icosahedral capsid.

helical capsid

A capsid can have a variety of structures; associated viruses may be referred to as _____.

helical or icosahedral viruses

A global epidemic is called a ______.

pandemic

The lysogenic cycle replicates the _____.

phage genome without destroying the host

The lytic cycle is a _____.

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

The viral envelope is usually derived from the host cell's ______.

plasma membrane as the viral capsids exit

Vaccines can _____.

prevent certain viral illnesses

Smaller, less complex entities called ______ also cause disease in plants and animals respectively.

prions

Since viruses can replicate only within cells, they _____.

probably evolved as bits of cellular nucleic acid

The intograted viral DNA is known as a _____.

prophage

The largest virus discovered's genome encodes _____.

proteins involved in translation, DNA repair, protein folding, and polysaccharide synthesis

The viral DNA that is integrated into the host genome is called a ____.

provirus

Natural selection favors bacterial mutants with surface proteins that cannot be _____.

recognized as receptors by a particular type of phage

Viruses cannot _____.

reproduce or carry out metabolism outisde of a host cell

Foreign DNA can be identified as such and cut up by cellular enzymes called _____.

restriction enzymes

The bacterium's own DNA is protected from the ______ by being methylated.

restriction enzymes

Viral nucleic acid molecules and capsomeres spontaneously _____.

self-assemble into new viruses

The genome of a virus is either a _____.

single linear or circular molecule of the nucleic acid

Viral glycoproteins on the envelope bind to ______.

specific receptor molecules on the surface of a host cell

H1N1 is the ______.

strain that caused the 2009 flu pandemic

Viral envelopes (derived from membranes of host cells) ______.

surround the capsids of influenza viruses and many other viruses found in animals

The RNA mlecules function both as mRNA for _______.

synthesis of viral proteins and as genomes for new virus particles released from the cell

Phages that use both the lytic and lysogenic cycles are called ______.

temperate phages

Other examples of emerging viruses include ______.

the chikungunya virus and the Zika virus (2015)

Flu epidemics are caused by ______; these infect a wide variety of animals including birds, pigs, horses, and humans

type A influenza viruses

In the late 1800's, researches hypothesized that _____ might be responsible for tobacco mosaic disease.

unusually small bacteria

The viral genome enters the host cell in a _____.

variety of ways

Viral envelopes contain a combination of ____.

viral and host cell molecules

A phage that reproduces only by the lytic cycle is called a _____.

virulent phage

Bacteriophages (phages):

viruses that infect bacteria

There are two key variable used to classify viruses that infect animals:

-an RNA or DNA genome, either single or double stranded -the presence or absence of a membranous envelope

Viral genomes may consist of either:

-double or single stranded DNA -double or single stranded RNA

Bacteriophages have an ______ that encloses their DNA.

enlonated capsid head

A vaccine is a ________.

harmless derivative of pathogenic microbes that stimulate the immune system to mount defenses against that harmful pathogen

Candidates for the source of viral genomes include ______.

plasmids and transposons

Strains of influenza A are given ______ based on the viral surface proteins hemagglutinin (HA) an neuraminidase (NA).

standardized names

The Cas protiens use the phage-related RNA to target _____.

the invading phage DNA

______, it can block any attempt of the same type of phage to reinfect it.

If the cell survives the infection

Some viruses have _____ that help them infect hosts.

accessory structures

When a phage infects a bacterial cell that has the CRISPR-Cas system, the pahge DNA _____.

is integrated between two repeat sequences

Later work suggested that the infectious agent did ______.

not share features with bacteria (such as the ability to grow on nutrient media)

Other viral membranes form from the host's ______ and are then replaces by an envelope made form Golgi apparatus membrane

nuclear envelope

A virus is a very small infectious particle consisting of _____.

nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope

Viruses exist in a shady area between life-forms and chemicals, leading a kind of ______.

"borrowed life"

What are the two major routes that plant viruses spread?

1. Horizontal transmission, entering through damaged cell walls 2. Vertical transmission, inheriting the virus from a parent

What three processes contribute to the emergence of new viral diseases?

1. RNA viruses have an unusually high rate of mutation 2. The disease can be disseminated from a small, isolated human population and can eventually spread around the world 3. About three-quarters of new human diseases originate by spreading to humans from animals

More than _______ types of viral diseases of plants are known and cause spots on leaves and fruits, stunted growth, and damaged flower or roots.

2,000

Viruses have between ____ genes in their genome.

3-2,000

HIV (human immunodeficiency virus) is the retrovirus that causes _____.

AIDS (acquired immunodeficiency syndrome)

Prions might also be involved in diseases such as _______.

Alzheimer's and Parkinson's disease

The largest virus yet discovered is the size of _____.

a small bacterium

Unlike a prophage, a provirus remains _____.

a permanent resident of the host cell

Each "spacer" sequence between the repeats corresponds to DNA from ____.

a phage that had infected the cell

Several prions _______ that can convert more proteins to prions.

aggregate into a complex

Most plant viruses have _____.

an RNA genome

What is a virus?

an infectious particle consisting of genes packaged in a protein coat.

In 2009, a general outbreak (epidemic) of a flu-like illness appeared in Mexico and the United States, caused by ______.

an influenza virus names H1N1

Each virus has a _____, which is a limited number of host cells that it can infect.

host range

Diseases caused by viral infections affect _______.

humans, agricultural crops, and livestock worldwide

New roads into a remote area may ______.

increase spread of viral diseases

Changes in host behavior or the environment can _______.

increase the spread of viruses responsible for emerging diseases

The broadest variety of RNA genomes is found in viruses that ______.

infect animals

Prions are _______.

infectious proteins that appear to cause degenerative brain diseases in animals

A protein tail piece attaches the phage to the host and _____.

injects the phage DNA inside

The use of _______ may help prevent the spread.

insecticides and mosquito nets

Viruses were detected indirectly ______.

long before they were actually seen

The lytic cycleproduces new phages and ______.

lyses (breaks open) the host's cell wall, releasing the progeny viruses

Many viruses that infect animals have ____.

membranous envelopes

Plasmids, transposons, and viruses are all _____.

mobile genetic elements

Viruses are _____.

much simpler in structure than even prokaryotic cells

Phages have two alternative reproductive mechanisms which are _____.

the lytic cycle and the lysogenic cycle

Prions are somehow able to convert a normal form of the protein into _____.

the misfolded version

A capsid is _____.

the protein shell that encloses the viral genome

An environmental signal can trigger _____ and switch to the lytic mode.

the virus genome to exit the bacterial chromosome

Viruses are obligate intracellular parasites, which means _____.

they can replicate only within a host cell

Emerging viruses are _____.

those that suddenly become apparent

The attempt of the pahge to infect the cell triggers _____.

transcription of the CRISPR region

Prions are incorrectly folded proteins, and can be _______.

transmitted in food, act slowly, and are virtually indestructible

Antiviral drugs can help to _______, viral infections by inhibiting synthesis of viral DNA and by interfering with viral assembly.

treat, not cure

The phage DNA is _____.

cut and destroyed

Whereas few bacteriophages have an envelope or an RNA genome, many animal viruses have _____.

both

Naturally selection favors phage mutants that ____.

can bind to altered cell surface receptors or that are resistant to enzymes

Viruses may damage or kill cells by ______.

causing the release of hydrolytic enzymes from lysosomes

In 1935, Wendell Stanley _____.

crystallized the infectious particle, now known as tobacco mosaic virus (TMV)


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