Chapter 6

induction

enivornmental change that leads to prophage excision

HeLa cells were the first...

first continuous tissue-culture cell line and were used to establish tissue culture as an important technology for research in cell biology, virology, and medicine

HeLa cell lines cultivated from

from tumor cells obtained from Henrietta Lacks, a patient who died of cervical cancer in

spiked proteins on HIV are called

gp120 gp 41

prions

infectious proteins acellular and don't contain DNA or RNA

s. When this cell-to-cell-contact occurs in primary cell cultures

mitosis is triggered to stop.

how do virusoids infect host cell?

need helper virus to infect host

life cycle of viruses with animal host cells: assembly

new phage particles are assembled

life cycle of viruses with animal host cells: release

new viral particles are made and released into the extracellular fluid. naked virus: lysis/burst of CW enveloped: bud off the surface for surface coating

specialized transduction: recombination

the phage DNA, along with the attached bacterial DNA, are incorporated into the new cell

specialized transduction: excision

the phage is excised from the bacterial chromosome along with a short piece of bacterial DNA. the DNA is then packed into newly formed capsids.

lysogeny

the process where lysogenic phage infects bacterial host

lysogenic cycle: what happens during poor environmental conditions?

the prophage DNA is excised from the bacterial chromosome and enters the lytic cycle -viral DNA active-->biosynthesis -maturation -lysis

continuous cell lines, usually derived from

transformed cells or tumors,

prions cause various forms of

transmissable spongiform encephalopathy in humans and animals

how do viroids replicate?

uses host to prelicate RNA

life cycle of viruses with animal host cells: uncoating

viral contents are released. capsid around genome is unpacked

life cycle of viruses with animal host cells: attachment

virus attaches to target cell

difference between virulent and temperate phages

Phages that replicate only via the lytic cycle are known as virulent phages while phages that replicate using both lytic and lysogenic cycles are known as temperate phages.

a prion is a misfolded rogue form of a normal protein

PrPc found in the cell

Creutzfeldt-Jakob disease

TSEs disease caused in humans---death of neuron cells

retrovirus

+ssRNA viruses with reverse transcriptase within capsid that synthesizes ssDNA using the +ssRNA genome as template. -ssDNA is made into dsDNA and can inegrate into host chromosome.

Which stages of the lysogenic cycle are the same as the ones in the lytic cycle?

-attachment, penetration -biosynthesis when viral DNA becomes activated -Maturation -Lysis

primary cell culture line

-freshly prepared from animal organs or tissues.

3 other ways to culture viruses?

-inject viruses fertilized chicken eggs like inside amniotic cavity, the choriollantonic membrane, or the yolk sac -Whole plant or animal -cell culture lines

latent infection

. There are viruses that are capable of remaining hidden or dormant inside the cell in a process called latency ex. chickenpox-->shingles

6. steps of life cycle of viruses with animal host cells:

1. attachment 2. penetration 3. uncoating 4. biosynthesis 5. assembly 6. release

Steps in HIV Retrovirus Replication (7)

1. gp120 binds to CD4 and then binds to the coreceptor 2. allows gp41 to fuse with the envelope of HIV and the host immune cell's cytoplasm: allows HIV nuncleocapsid to enter the host cell 3. enzyme transcriptase will convert viral RNA genome into ds DNA 4. viral DNA is incorporated into the host DNA 5. new viral RNA is used as genomic RNA and makes viral proteins 6. new viral RNA and proteins move to cell surface, and new immature HIV forms 7. Host cell places protein spikes on plasma membrane, so when virus buds off, it can have them as part of envelope when virus matures.

Steps of culturing viruses: Plaque Assay (3) 1. what does the mixture contain? (3)

1. mixture containing molten top agar, bacterial cells(hosts) and DILUTED phage are poured onto a solidified nutrient agar plate. (4 moisture 4 host to survive) 2. mixture is left to solidify 3. incubation allows for bacterial growth and plaque replication -lawn of host cells

5 steps of specialized transduction

1. viral attachment and penetration 2.integration 3.excision 4.infection 5.recombination

lysogen

A bacterial host with a prophage is called a lysogen. -bacteria once prophage is established

life cycle of viruses with animal host cells: penetration

After binding to host receptors, animal viruses enter through endocytosis (engulfment by the host cell) or through membrane fusion (viral envelope with the host cell membrane).

host immune cell needs what receptor on its surface and what coreceptor for the virus to gain entry?

CD4 protein: CCR5 or CXCR4

prophage

During the lysogenic cycle, instead of killing the host, the phage genome integrates into the bacterial chromosome and becomes part of the host. The integrated phage genome is called a prophage

filtration

Filters can physically remove anything present in the solution that is larger than the virions; the viruses can then be collected in the filtrate

tissue tropism

Many viruses are host specific, meaning they only infect a certain type of host; and most viruses only infect certain types of cells within tissues.

lysogenic conversion

The presence of the phage may alter the phenotype of the bacterium, since it can bring in extra genes (e.g., toxin genes that can increase bacterial virulence). This change in the host phenotype is called lysogenic conversion.

Lytic Cycle: Penetration

The viral DNA penetrates into the host cell. When attached, the phage undergoes conformational changes in its capsid releases LYSOZYME to break down the cell wall of the host. this shape change will allow it to inject its genetic material through the hole into area of host cell.

contact inhibition

When cells in a primary culture undergo mitosis and a sufficient density of cells is produced, cells come in contact with other cells. When this cell-to-cell-contact occurs, mitosis is triggered to stop. and it prevents the density of the cells from becoming too high

chronic infection

a disease with symptoms that are recurrent or persistent over a long time. ex. HIV

the rogue prion protein (PrPsc) may be caused by

a genetic mutation or spontaneously, can be infectious and cause other endogenous normal proteins to become misfolded, forming plaques.

Because of anchorage-dependence requirements, primary cell cultures require

a liquid culture medium in a Petri dish or tissue-culture flask so cells have a solid surface such as glass or plastic for attachment and growth.

persistent infection

a virus is not completely cleared from the system of the host but stays in certain tissues or organs of the infected person. The virus may remain silent or undergo productive infection without seriously harming or killing the host.

how do prions affect the brain and nervous system?

accumulation of rogue proteins causes the brain tissue to become sponge-like, killing brain cells and forming holes in the tissue, leading to brain damage, loss of motor coordination, and dementia -can't move or speak

some virusoids are also pathogens in

animals -hepatitis delta virus

Lytic Cycle: Maturation

assembly of viral components genome into capsid

5 steps of bacteriophage lytic cycle?

attachment penetration biosynthesis maturation release

What is the lytic cycle?

bacteriophage takes over the cell, reproduces new phages, and destroys the cell.

life cycle of viruses with animal host cells: biosynthesis

can occur in cytoplasm or nucleus depends on virus END RESULT: copy genome and pieces that will become parts of the virus

To prevent contact inhibition....and is called.....

cells from the primary cell culture must be transferred to another vessel with fresh growth medium. This is called a secondary cell culture.

Virions in the liquid medium can be separated from the host cells by either

centrifugation or filtration

specialized transduction occurs...

occurs at the end of the lysogenic cycle, when the prophage is excised and the bacteriophage enters the lytic cycle -can excise host and viral genes together -after whole cycle, end up with phages have both genes! -infect next host, inject both genomes and cause changes in new host cell -viruses delivering genes to a new bacteria and change its genome

transduction

occurs when a bacteriophage transfers bacterial DNA from one bacterium to another during sequential infections

how is continuous cell lines different from primary?

often able to be subcultured many times or even grown indefinitely often able to be subcultured many times or even grown indefinitely

Lytic animal viruses follow similar infection stages to bacteriophages: attachment, penetration, biosynthesis, maturation, and release . However, the mechanisms of _____, ______, and _______ differ between bacterial and animal viruses

penetration, nucleic-acid biosynthesis, release

Lytic Cycle: Biosynthesis

phage DNA replicates and phage proteins are made. viral's genetic material will be able to code for replication of all the DNA of the next generation of virions. use genome of host for transcription and translation of genes for viral capsids to be made. makes different components that will become the next generation of viruses

specialized transduction: infection

phage containing both viral and bacterial DNA infect a new host cell

specialized transduction: Viral attachment and penetration

phage infects a cell

virusoids are pathogens in

plants

Viroids are pathogens of

plants -ex. potato tuber spindle disease

. For lytic bacteriophages, lysing of the bacterial hosts can then be readily observed when a clear zone called a

plaque As the phage kills the bacteria, many plaques are observed among the cloudy bacterial lawn. -areas of host cell death

the inetegrated viral genome of retroviruses are called

provirus

virusoids genome protein coat?

short strand of circular RNA no protein coating

viroids genome protein coat?

short strands of RNA with no protein coat to protect genome

Lytic Cycle: Attachment

surface of the phage attaches to host cell's surface receptors -phages are very host specific

lysogenic cycle: what happens after establishing prophage?

the cell divides, and prophage DNA is passed onto daughter cells

Lytic Cycle: Lysis

the cell lyses, releasing the newly made phages. end of replication cycle. viral DNA will code for large amounts of LYSOZYME. it will come in contact with cell wall and put damage to cell wall to release the phages. makes the environment hypotonic (more conc. inside causes the cell to lyse)

How is the lysogenic cycle different from the lytic cycle?

the host can be infected with virus's genome but host is not harmed and can still reproduce itself, but if the viral genome gets activated, it will cause the destruction of the host

specialized transduction: integration

the phage DNA becomes incorporated into the host genome

lysogenic cycle: what happens after the phage penetrates into the host cell?

the phage DNA becomes incorporated with the host genome, establishing prophage. -when viral DNA is in prophage state, it is not directing any activity to replicate the viruses