bio chapter 19 : viruses

phage lytic cycle

1. attachment 2.entry of phage DNA and degradation of host DNA 3.syntehsis of viral genomes and proteins 4.self assembly - the new proteins and DNA constructed rebuild new phages -includes a head, tail , tail fibers 5.release

reverse transcriptase has two functions which are

1. copying the DNA molecule made from the RNA ( using DNA polymerase) 2. degrading the RNA molecule brought in

the emergence of new viruses onto the scene ; how does this happen

1.mutations of existing viruses 2.the dissemination of a viral disease from a small isolated human population 3. new viral disease in humans is the speed of existing viruses from other animals

Which replicative cycle describes a virus that can integrate its genome into the host cell's genome?

A lysogenic virus can integrate its genome into the host cell's genome and be duplicated by the host cell's replication machinery.

Define the following parts

A. glycoprotein b. viral envelope c. reverse transcriptase enzyme d. e. viral genome ( RNA , genes of the HIV molecule) HIV is two single strands of RNA

Which of the following is an example of vertical transmission of a virus in plants?

An infected plant produces seeds that contain the virus, giving rise to infected progeny.

lytic and lysogenic facts

Bacteriophages, which contain double-stranded DNA, can reproduce by two alternative mechanisms: the lytic cycle and the lysogenic cycle. In the lytic cycle, virus parts are made, new viruses are assembled, and the cell is lysed, releasing the newly assembled viruses. In the lysogenic cycle, the viral DNA incorporates into the bacterial DNA and is passed on to daughter bacterial cells when the infected bacteria reproduce normally. Occasionally, an infected bacterium in the lysogenic cycle can enter the lytic cycle, in which viral particles are produced and the cell is eventually ruptured.

Candidates for the original source of viral genomes include __________.

Candidates for the original sources of viral genomes include plasmids and transposons. Viruses have been found that infect every form of life—not just bacteria, animals, and plants but also archaea, fungi, and algae and other protists. Because they depend on cells for their own propagation, it seems likely that viruses are not the descendants of precellular forms of life but instead evolved—possibly multiple times—after the first cells appeared. Most molecular biologists favor the hypothesis that viruses originated from naked bits of cellular nucleic acids that moved from one cell to another, perhaps via injured cell surfaces. The evolution of genes coding for capsid proteins may have allowed viruses to bind cell membranes, thus facilitating the infection of uninjured cells. Plasmids are small, circular DNA molecules found in bacteria and in the unicellular eukaryotes called yeasts. Plasmids exist apart from and can replicate independently of the bacterial chromosome, and are occasionally transferred between cells. Transposons are DNA segments that can move from one location to another within a cell's genome. Thus, plasmids, transposons, and viruses all share an important feature: They are mobile genetic elements.

How does a retrovirus like HIV enter a host cell?

Glycoproteins on the viral envelope bind to receptors on the host cell. The viral envelope fuses with the host cell's plasma membrane, facilitating uptake of the virus by the host cell.

How does HIV cause disease?

HIV kills cells that defend the body against disease. Takes over helper T cells HIV affects the immune system and kills cells that protect the body from foreign bacteria and viruses. -attacks the CD4 protein

Why can flare-ups of herpes virus infection recur throughout a person's life?

Herpes virus can leave its DNA behind as minichromosomes in nerve cell nuclei. Stress can trigger another round of virus production, producing characteristic blisters and sores. In the case of herpes virus, copies of the viral DNA can remain behind as minichromosomes in the nuclei of certain nerve cells. There they remain latent until some sort of physical or emotional stress triggers a new round of active virus production. The infection of other cells by these new viruses causes the blisters characteristic of herpes, such as cold sores or genital sores. Once someone acquires a herpes virus infection, flare-ups may recur throughout the person's life.

lysogenic cycle

Integration of viral DNA into host DNA is an early stage of the lysogenic cycle. -Viral DNA, incorporated into host DNA as a prophage, is replicated along with host DNA.

What is the function of reverse transcriptase?

It catalyzes the formation of DNA from an RNA template. Retroviruses are equipped with an enzyme called reverse transcriptase, which makes a DNA copy of an RNA template, providing information flow from RNA to DNA.

How do prions, which are misfolded proteins, infect organisms?

Prions are a misfolded version of a protein normally found in the brain. When prions come into close proximity with the normal proteins, they cause them to refold into the prion form.

How do prions propagate and replicate themselves?

Prions convert normal proteins into the misfolded prion version.

When comparing DNA and RNA viruses, which mutate more quickly, and why?

RNA viruses, because no proofreading is done on RNA molecules

How are retroviruses different from other types of viruses?

Retroviruses use the enzyme reverse transcriptase to transcribe a copy of DNA from their own RNA.

Which of the following is not a class I virus? adenovirus polyomavirus parvovirus poxvirus papillomavirus herpesvirus

THE CORRECT ANSWER parvovirus Parvovirus is a class II virus, not a class I virus. Like all viruses, those that cause illness in humans and other animals can replicate only inside host cells. Many variations on the basic scheme of viral infection and replication are represented among animal viruses. One key variable is the nature of the viral genome (double- or single-stranded DNA or RNA), which is the basis for the common classification of viruses. Single-stranded RNA viruses are further classified into three classes (IV-VI) according to how the RNA genome functions in a host cell.

The H1N1 2009 outbreak is considered to have been which of the following?

The 2009 outbreak is considered a pandemic even though its death toll was much lower than that of 1918-1919 pandemic. H1N1 virus was a mix of bird and swine flu coupled with a mutation

The avian flu virus H5N1 is considered a greater long-term threat than the swine flu virus H1N1 because __________.

The avian flu virus H5N1 is considered a greater long-term threat than the swine flu virus H1N1 because it has a significantly higher mortality rate. The overall mortality rate of the H5N1 virus is greater than 50%. Furthermore, the host range of H5N1 is expanding, which provides increasing opportunities for different strains of the virus to reassort their genetic material and for new strains to emerge. If the H5N1 avian flu virus evolves so that it can spread easily from person to person, it could represent a major global health threat akin to that of the 1918 pandemic.

The lytic cycle of bacteriophage infection ends with the _____. As a result of the lytic cycle, _____.

The bacterium ruptures and phages are released. The host cell's DNA is destroyed, and ultimately, the host cell itself is destroyed in the lytic cycle.

Which of the following events occurs during the lytic life cycle of phages?

The host cell usually dies, releasing many new copies of the virus.

What is the source of a viral envelope?

The viral envelope is derived from host cell membrane. on the new virus the envelope - if obtained is from the hosts cell membrane that is pinched off as a vesicle as it leaves the cell

How does HIV bind to a host cell?

The viral envelope proteins gp120 and gp41 interact with CD4 and a co-receptor on the host-cell membrane.

Why are retroviruses considered a special class of viruses?

They transcribe RNA to DNA using reverse transcriptase. Retroviruses reverse the normal flow of information, forming a DNA provirus from an RNA genome.

Which of the following statements correctly describes one difference between virulent phages and temperate phages?

Virulent phages replicate through the lytic cycle only, and temperate phages replicate using both the lytic and the lysogenic cycles.

vaccine

a harmless variant or derivative of pathogen that stimulates the immune system to mount defense against a harmful pathogen

lytic cycle virulent phage

a phage replicative cycle that culminates in death of the host -this actually refers to the last stage of infection during which the bacterium lyses and release the phages that were produces in which they can infect a healthy cell. -a few successive lytic cycles can destroy an entire bacterial population in hours -a phage that replicates only through a lytic cycle is a *virulent phage*

The genetic material of HIV consists of _____.

a single stranded RNA two molecules of a these single stranded RNA +two enzymes of reverse transcriptase

retrovirus reverse transcriptase integrase

a virus that carries along an enzyme called *reverse transcriptase* which allows it to insert its own RNA to reverse the process of transcription and highjack the cells DNA making facility to produce its new infected DNA reverse transcriptase - an enzyme in retrovirus viruses that allows viruses to transcribe DNA from a brought in RNA -in HIV's case it brings in its own RNA and the reverse transcriptase enzyme which immediately copies the RNA of the virus once in the cells cytoplasm . from here the new DNA transcribes off itself to form a double stranded DNA of the virus and merges into the nucleus of the host cell where it becomes a *provirus* and merges into the DNA of the host cell it is carried into the host cells nucleus to merge with host cell DNA through the enzyme *integrase*

viral envelope

a virus with not only a capsids but also an outer membrane that is passed from a host cells membrane prior not all viral envelopes have spikes or glycoproteins

Prions are __________ that are thought to cause disease by __________.

abnormally shaped proteins; inducing similar but normally shaped proteins in the brain to adopt the abnormal form

prophage

after phage bacteria has entered host bacteria and linked its DNA with the host DNA it is called *prophage* prophage - viral DNA that is integrated into the bacterial chromosome and merges as one. this takes place during a lysogenic ( joining while maintaining the host) process provirus - the same concept of a prophage but in animal cells instead of bacteria cells

HIV information cell replication

after the virus is in provirus form it can form now mRNA that leaves the nucleus -these new mRNA can code for new ribosomes to produce new types of proteins in the cells ER. The ribosomes will bound to the ER and be processed even eventually flow over to the Golgi for further processing. After being processed they are moved over to the cellular membrane with their new spiked membrane that is now covering the host cell to be used to allow the newly formed protein to flow out of the host cell -free ribosomes form a poly peptide to form new viral protein that are formed into a viral particle and buds with the new cell membrane -this continues to process but eventually the cell will die

Why are viruses called obligate intracellular parasites? They must use a host cell's amino acids to synthesize proteins. They must use a host cell's nucleotides for transcription and replication. They must use a host cell's metabolic enzymes and pathways to obtain energy. They must use a host cell's ribosomes to synthesize proteins. All of the above.

all of the above A virus needs a host cell to perform all of these functions (and more). They are obligated to use the intracellular of the host as parasites

lysogenic cycle- temperate phages

allows replication of the page genome without destroying the host -phages capable of using both modes of replication are called *temperate phages* -prophage - during a lysogenic cycle - the DNA molecule is incorporated into a specific site on the chromosome by viral proteins that break both circular DNA molecules and join them together . When integrated into the bacterial chromosome in this way it is known as a prophage - -- one prophage gene codes for a protein that prevents transcription of most of the other prophage genes, in which the phage genome is mostly silent

virus

an infectious particle consisting of a little more than genes packed into a protein coat -they cannot reproduce on their own and must hijack a host and infect their DNA and inject the virus DNA to take over the cell -are very small and the smallest of them are smaller than a ribosome -viruses can be in many forms , double DNA or RNA, or single DNA or RNA based on the nucleic acid that makes up its genome

spikes (glycoproteins)

another common name for *glycoproteins* that are on the viral envelope or membrane of viruses with these envelopes -are used as methods for attachment to hosts -also important in recognizing the correct host cells to infect Glycoproteins on the viral envelope recognize and bind to receptors on the host cell.

define the picture on the answer slide

apparently this is the phages 'protein coat' - the cylinder like base is also a part of the protein coat - the legs latch onto the bacteria and sits down and injects the viruses DNA information into the bacteria host -from here the bacteria host DNA is destroyed and the virus bacteria is replicated through its cell process -in a lytic process the cell would lyse as the end of the new virus phage proteins pushing out

Viruses that infect bacteria are called __________.

bacteriophages

To cause a human pandemic, the H5N1 avian flu virus would have to

become capable of human-to-human transmission.

viroids

circular RNA molecules only a few hundred nucleotides long, that infect plants -much smaller than viruses -usually disrupts growth in plants so infected plants will have stunted growth or abnormal development

Classes of viruses

class 1. double strand DNA 2. single strand DNA 3. double strand RNA 4. single strand RNA ( serves as mRNA 5.serves as a template for mRNA synthesis 6.serves as a template for DNA synthesis

Restriction enzymes help defend bacteria against viral infections by __________.

cutting viral DNA once it has entered the cell

host range

each particular virus can infect cells of only a limited number of host species called the host range -the virus usually indeitfies host cells by lock and key fit used on viral surface proteins and receptors molecules on the outside of cells -some viruses have broad host cell range like west nile virus while some have limited host range and can only infect certain species

emerging viruses pandemic epidemic

emerging viruses - virus that suddenly become apparent epidemic - a widespread outbreak pandemic - global epidemic

True or false? The human immunodeficiency virus (HIV) uses reverse transcriptase to make double-stranded RNA copies of its DNA genome.

false A retrovirus such as HIV has an RNA genome and uses reverse transcriptase to make double-stranded DNA copies of the genome, which can then be integrated into the host cell's genome.

Which of the following characteristics, structures, or processes is common to both bacteria and viruses?

genetic material made of nucleic acids - viruses do not have any organelles -cannot self reproduce, need a host cell -Viruses are nonliving intracellular parasites that infect plants, animals, and bacteria. Viruses use host cell components to make copies of themselves. Often, but not always, the process of viral replication kills the host cell.

Vaccines for viral diseases are __________ and help prevent infection by __________.

harmless derivatives of pathogenic viruses; stimulating the immune system to mount a defense against the actual pathogen Effective vaccines are also available to protect against rubella, mumps, hepatitis B, and a number of other viral diseases.

prions

infections proteins - -appear to cause a number of degenerative brain diseases in various animal specifies -mad cow disease -traditionally picked up from eating infected meat , cannibalism -two main characteristics - 1 prions act very slowly, up to 10 year incubation period 2. they are nearly indestructible the fact they take so long to develop its too late to identify and diagnose -they have the ability to spread by forcing the shape of other proteins to take on their similar shape somehow, in which they are misfolded proteins -several prions will get together and form a complex where they begin to force other proteins into their own shapes

viral envelope production

it can be observed that even the ER is highjacked in this host cell to produce the new parts of the host cells membrane to produce spiked membranes that the new copies of the phages can use exocytosis to take new spiked membrane with them

A phage that inserts itself into the host DNA is called __________.

lysogenic another definition would be a page that incorporates its own DNA in the DNA of the host and continues to reproduce from here

The phage reproductive cycle that kills the bacterial host cell is a __________ cycle, and a phage that always reproduces this way is a __________ phage.

lytic ; virulent

Animals that harbor and can transmit a particular virus but are generally unaffected by it are said to act as a __________ for that virus.

natural reservoir Animals that are natural reservoirs for viruses are capable of transmitting the viruses to other organisms.

phages are only created during which process? lytic or lysogenic?

only created during lytic lysogenic continue to produce its regular genetic material mixed along with the infected DNA ( prophage or provirus)

When a virus infects an E. coli cell, what part of the virus enters the bacterial cytoplasm?

only the nucleic acid enters - the phage breaks off but basically shoots its genetic material into the host cell

What do we call a virus that attacks a bacterium?

phage Viruses that infect bacteria are called bacteriophages or, simply, phages.

All of the following types of viruses have envelopes except __________. rhabdovirus retrovirus herpesvirus flavivirus poxvirus picornovirus

picornovirus - no envelopetitus

Double-stranded viral DNA is incorporated into a host cell as a _____

provirus "Provirus" is the name given to double-stranded viral DNA that has been incorporated into a host cell's genome.

Class IV viruses are characterized by which of the following types of genomes?

single stranded RNA that serves as mRNA

viral envelopes

some viruses have accessory structures that help them infect their hosts -this membranous envelope surrounds the capsids of influence and many others -the envelopes are derived from the membranes of the host cell

temperate phages

temperate phages are phages capable of using both modes of replicating within a bacterias -a temperate phage is called 'lambda' -there are times when the lysogenic phase can switch over to the lytic cycle -this is usually signaled by environmental factors

viral diseases in plants

tend to spread two ways horizontally - the spreading from plant to plant next to each other -cannot necessarily be by touch usually have to receive the sapp from another plant , can be spread by herbivores eating and carrying and disposing over the material , farmers from shearing plants -Vertically - from plant parent

HIV

the most important retrovirus is enveloped and made of two single RNA strand and also two molecules of reverse transcriptase -human immunodeficiency virus -causes AIDS (acquired immunodeficiency syndrome ) -this forms as a *provirus* as the RNA changes the DNA to contain part of the virus's DNA and continue to produce with the new infected DNA

Viruses can vary with respect to all of the following characteristics except __________. DNA or RNA as the genetic material presence or absence of a membraneous envelope single or double stranded nucleic acids the presence or absence of metabolic machinery they type of host it can infect

the presence or absence of metabolic machinery all the other information are ways that viruses can vary . -viruses do not have metabolic machinery they are not living organisms on their own

capsid

the protein shell enclosing the viral genome -depending on the virus the capsid may be rod shaped, polyhedral or more complex in shape -capsids are made from a large number of proteins called capsomeres the following of the shapes of the pictures 1.helical viruses 2.icosahedral capsid ( adenoviruses) 3.viral envelope (influenza) 4.bacteriophage ( head and tail )

virulent

the type of phage that is produced from a lytic cycle

HIV, the virus that causes AIDS, only infects certain cells within the immune system. This is because __________.

the virus binds to specific receptors that are only present on certain immune cells

restriction enzymes

these restrict the ability of a phage to replicate within the bacterium as they will identify the page and cut it up with cellular enzymes -this is one advancement or evolution of the bacteria -some bacterias have developed certain surface proteins that are no longer recognizable by phages so they do not enter, natural selection - some bacteria will use a process called *lysogeny* - the host is not killed by the bacteria rather lives with it

How do enveloped viruses differ from nonenveloped viruses?

they have an outer membrane covering outside of the capsid Enveloped viruses have a membrane-like outer covering (an envelope) surrounding their capsid.

many of the symptoms associated with viruses such as body aches and fever are a result of the body trying to fight the virus True or false

true

the way the virus enters the cell depends on the type of virus

true -the virus will enter the cell and begin to release its proteins which will hijack the DNA replication process and produce more of the virus and the viral progeny exit the cell

What is the most effective way to stop viral infections?

vaccines Correct Vaccines stimulate the immune system to recognize and effectively fight off invading viruses. They have proven to be the most effective weapon against viruses.

Circular RNA molecules that function like a virus in plants are termed __________.

viroids

Why are viruses often considered to be nonliving?

viruses do not carry out metabolic processes, a primary characteristic of living organisms

bacteriophages ( phages)

viruses that infect bacteria have head and tail