BIO 202 Chapter 27- virus

Prophage

A prophage is a bacteriophage genome inserted and integrated into the circular bacterial DNA

vaccine

A vaccine is a harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the harmful pathogen ● Vaccines can prevent certain viral illnesses ● Viral infections cannot be treated by antibiotics ● Antiviral drugs can help to treat, not cure, viral infections by inhibiting synthesis of viral DNA and by interfering with viral assembly

humans and animals

About three-quarters of new human diseases originate by spreading to humans from animals

CRISPR Cas mechanism

CAS proteins snip the viral DNA The cut viral DNA is inserted into places on the Host cells genome The cut viral DNA in the genome is marked and a corresponding RNA sequence to it is made The RNA sequence is attached to CAS PROTEINs. Now this can precisely cut corresponding viral DNA

capsid and capsomere

Capsid is the protein shell that encloses a viral genome capsids are built from subunits called capsomeres

capsids and capsomeres

Capsids are built from a large number of protein subunits called capsomere

DNA vs RNA virus mechanism of replication

DNA viruses use the DNA polymerases of the host cell to synthesize new genomes along the templates provided by the viral DNA RNA viruses use virally encoded RNA polymerase that can use RNA as a template

viruses as pathogens

Diseases caused by viral infections affect humans, agricultural crops, and livestock worldwide

genetic material in HIV

HIV and other retroviruses are enveloped viruses that contain two identical molecules of SS RNA and two reverse transcripateses

viral disease in plants

More than 2,000 types of viral diseases of plants are known and cause spots on leaves and fruits, stunted growth, and damaged flowers or roots ● Most plant viruses have an RNA genome ● Many have a helical capsid, while others have an icosahedral capsid

lysogenic propogation

One prophage gene codes for a protein that prevents transcription of most of the other prophage genes. Thus, the phage genome is mostly silent within the bacterium. Every time the E. coli cell prepares to divide, it replicates the phage DNA along with its own and passes the copies on to daughter cells. A sin- gle infected cell can quickly give rise to a large population of bacteria carrying the virus in prophage form. This mechanism enables viruses to propagate without killing the host cells on which they depend.

prions as infectious agents

Prions are infectious proteins that appear to cause degenerative brain diseases in animals ● Scrapie in sheep, mad cow disease, and Creutzfeldt-Jakob disease in humans are all caused by prions ● Prions are incorrectly folded proteins, can be transmitted in food, act slowly, and are virtually indestructible

the lytic cycle of a phage T4 5 steps

T4 is a virulent phage

Animal virus replication

There are two key variables used to classify viruses that infect animals: ● An RNA or DNA genome, either single-stranded or double-stranded ● The presence or absence of a membranous envelope

viral diseases in animals

Viruses may damage or kill cells by causing the release of hydrolytic enzymes from lysosomes ● Some viruses cause infected cells to produce toxins that lead to disease symptoms ● Others have molecular components such as envelope proteins that are toxic

difference between phage and animal virus

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

virulent phage

a phage that only reproduces by the lytic cycle

viral envelope -what i it? -what i it made from ?

a type of accessory structure a membranous envelope which surrounds the capsids of viruses the envelope is designed from the membrane of the host cell- contain host cell phospholipids, membrane proteins in addition to glycoproteins from the virus

general structure of a virus -it may have

a virus is a very small infectious particle consisting of nucleic acid that is enclosed in a protein coat sometimes a membranous envelope

bacteriophages

a virus with a complex capsid found among the viruses that infect bacteria an icosahedral head capsid attached to a tail like apparatus

lysogenic cycle

allows replication of the phage w/o destroying the host cell the viral DNA molecule is incorporated into the host genome

Virus

an infectious particle consisting of genes (nucleic acid) inside of a protein coating

viruses do not fit our definition of living organisms

an isolated virus is biologically inert, unable to replicate its gene, or regenerate its own supply of ATP

prions

an organism that does not replicated but still causes infection a misfolded form of a protein normally present in brain cells when prion gets into a cell with the normal form of the protein, it converts the normal protein to misfolded versions prions then aggregate into complex that convert other normal proteins to prions

Phages have two alternative reproductive mechanisms -what is there genome typically

by the lytic cycle of the lysogenic cycle

increase of spread of a virus

changes in host behavior or the environment new roads into remote areas global climate change allowing mosquitos to increase their range

CRISPR CAS SYSTEM stands for

clustered regularly, interspaced, short palindromic repeats

Wendell Stanley

confirmed the virus hypothesis by crystallizing the infectious particle known as TMV

Ivanowsky -designed and hypothesized? -disproved by ? which showed?

designed a filter to remove what was thought to be bacteria. However, after filtration there was still bacteria hypothesized that the bacteria was small enough to pass through filter or created a toxin that allowed to toxin was disproved by beijernick- showed that infectious agent in filtered sap could replicate

host range

each particular virus can only infect cells of a limited number of host species

simplified viral reproductive cycle

entry and uncoating replication transcription and manufacture of capsid proteins self assembly of new virus particles and exit fro cell

epidemic vs pandemic

epidemic is a general outbreak pandemic- a global epidemic

Beijernick was first to -he imagined ?

first person to voice the theory of a virus- imagined a replicating pathogen much smaller than a bacteria

Adolf mayer

found that he could transmit tmd from plant to plant by rubbing the spas extracted

different shapes of viruses

helical- a rigid, rod shaped virus icosahedron - protein molecules arranged in a polyhedral capsule more complexed

two transmissions of plant spread

horizontal transmission- entering through damaged cell wall vertical transmission- inheriting the virus from a parent

viruses were detected

indirectly before they were seen

viruses genome

is either a linear or circular molecule of nucleic acid some viruses consist of multiple molecules of nucleic acid.

number of different kinds of proteins in a virus

is usually small

lytic cylce

is when a phage replicative cycle culminates in the death of the host cell refers to the last step in which new phages break open the cell wall of the host in order to release the new viruses

evidence of mobile elements

it appears as if the genomes of some viruses are very similar to the genomes of the organisms that they infect some animal viruses are similar to plant viruses- persistence of groups of viral genes that were favored by natural selection during early evolution of viruses and eukaryotes that served as their hosts

Why have bacteria not gone extinct from lytic phages (3) -restrictive enzyme are ?

natural selection favors bacteria whose receptors are not recognized by a virus restrictive enzymes- when phage DNA infiltrate a bacterium the dNA is identified as foreign and cut up by these cellular enzymes. The cells own DNA is methylated so it is not attacking itself lysogeny

are all viruses envelopes derived from plasma membrane?

no herpsevirus are cloaked in membrane derived from the nuclear envelope of the host

viroids

organisms smaller than viruses that infect plants circular RNA molecules do not encode proteins but can replicate in plant host cells - a single molecule can be an infectious agent that spreads disease

accessory structures

some viruses have accessory structures that help them to infect cells

temperate phage

temperate phages, such as lamba are capable of using the lysogenic and lytic cycle

Beijernick also found

the "bacteria" could not be grown on medium

Animal viral genetic material

the broadest variety of RNA genomes is found in viruses that infect animals

host range results from

the evolution of recognition systems by the virus viruses usually identify host cells by a lock and ket fit between viral surface proteins and specific receptor molecules on the outside of cells

viruses that use RNA to RNA

the genome of class IV directly serve as mRNA, meaning that it ca be translated into protein right after infection in class V, RNA genome serves as template for mRNA In class VI, ssRNA serves as a template for DNA synthesis (retrovirus) All viruses that use RNA to RNA use a viral enzyme for this

mimivirus

the largest virus discovered in size- the size of a small bacterium genes code for products thought of be the hallmark of cellular genomes- proteins involved in translation, DNA repair, protein folding, polysaccharide syntheses

how to emergent viruses occur

the mutation of an existing virus - RNA has high rate of mutation because replication errors are not corrected dissemination of a viral disease from a small, isolate human population spread of existing viruses from animals

Crispr CAS lecture explanation

the phage DNA is integrated within two repeat sequences If the cell survives the infection, it can block any attempt of the same type of phage to reinfect it The attempt of the phage to infect the cell triggers transcription of the CRISPR region The resulting RNAs are cut into pieces and bound by Cas proteins The Cas proteins use the phage-related RNA to target the invading phage DNA The phage DNA is cut and destroyed Natural selection favors phage mutants that can bind to altered cell surface receptors or that are resistant to enzymes The relationship between phage and bacteria is in constant evolutionary flux

lytic and lysogenic cycle of a phage steps

the phage binds to the surface of the cell and injects its linear DNA Within the host, the lambda molecule forms circle IF lytic cycle - the viral genes immediately turn the host cell into a lambda producing factory and burst open the cell if lysogenic- the lambda DNA is incorporated into a specific site in the host chromosome, becoming a prophage one prophage gene encodes for a protein that prevents transcription of other prophage genes When the cell prepares to divide, it replicates the prophage NA along with its own

once a viral genome enters the cell

the protein it encodes can commander the host, reprogramming the cell to copy the viral nucleic acid and manufacture viral proteins the host provides all the necessary material for making viral NA, enzymes, tRNAs, amino acids, ATP and other molecules viral nucleic acid molecules and capsomere spontaneously self-assemble into new viruses

protein tail piece

the protein tail piece uses it fibers to attaches the phage to the host and injects the phage DNA inside

variations in genome size

the smallest viruses have four genes in their genomes. The largest have several hundred to one thousand

viruses differ on their genomes - two factors

there are DNA viruses and RNA viruses can be double or single stranded DNA can be double or single stranded RNA

why may viruses not be considered alive (2)

they cannot reproduce they cannot carry out metabolic processes outside of a host cell

lysogenic can become lytic

this occurs when the genome is induced to exit the bacterial chromo- some and initiate a lytic cycle. An environmental signal, such as a certain chemical or high-energy radiation, usually triggers the switchover from the lysogenic to the lytic mode.

how are viruses connected to the living world

through their use of genetic material

discovery of viruses

tobacco mosaic disease stunts growth of tobacco plants, gives the leaves a mosaic coloration

candidates for the source of viral genomes

transposons-DNA segments that can move from one location to another within a cells genome. plasmids-small, circular DNA molecules found in bacteria and yeast They are all mobile genetic elements-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 sur- faces.

retroviruses

use reverse transcriptase to copy their ssRNA genome into dsDNA HIV is a retrovirus that cuases AIDS

early thoughts on viruses -first thought to be -saw parallels to __due to ___?

very early on they were thought to be chemicals in 1800s, it was proposed that they were the simplest life forms saw a parrallel to bacteria due to ability to cause disease and spread

membrane envelopes are used to enter host cell

viral glycoproteins on the envelope bind to specific receptor molecules on the surface of the host cell ; cellular enzymes in the ER and Golgi apparatus then add the sugars. The resulting viral glycoproteins, embedded in host cell-derived membrane, are transported to the cell surface. new viral capsids are wrapped in the membrane as they bud off from the hot cell

debate on which came first

virus before - mimivurus may propose that viruses evolve before the first cell and developed an exploitative relationship with them virus after- evolved after and has been scavenging genes from hosts

viruses are parasites -why, what do they lack?

viruses are obligate intracellular parasites-they can only replicate inside of a cell they lack metabolic enzymes and equipment for making proteins

limitations within an organism

viruses that can affect multicellular eukaryotes are only able to affect one type of tissue

Emerging viruses

viruses that suddenly become apparent ebola, HIV, ZIKa

how does a viral infection begin entry depends on ?

when a virus binds to a host cell and the viral genome makes its way inside the mechanism of entry depends on the type of virus and type of host cell- For example, T-even phages use their elaborate tail apparatus to inject DNA into a bacterium Other viruses are taken up by endocytosis or, in the case of enveloped viruses, by fusion of the viral envelope with the plasma membrane.

influenza

● Flu epidemics are caused by type A influenza viruses; these infect a wide variety of animals including birds, pigs, horses, and humans ● Strains of influenza A are given standardized names based on the viral surface proteins hemagglutinin (HA) and neuraminidase (NA) ● H1N1 is the strain that caused the 2009 flu pandemic

DNA to RNA IN animal viruses

● The viral DNA that is integrated into the host genome is called a provirus ● Unlike a prophage, a provirus remains a permanent resident of the host cell ● RNA polymerase transcribes the proviral DNA into RNA molecules ● The RNA molecules function both as mRNA for synthesis of viral proteins and as genomes for new virus particles released from the cell