Unit 3.3 viruses

viruses

noncellular entities that are parasites of cells

oncogene

transform normal cells into cancerous cells

pathogens

disease causing, microorganism that causes disease

viruses vs bacteria

bacteria are living organisms and viruses look at diagram

viral shapes

helical (hollow cylindrical capsid), polyhedral (many sides), enveloped, complex (complicated structure)

general structures of viruses

require host cells to multiply (obligatory intracellular parasites), contains DNA or RNA, contains protein coat, no ribosomes, no ATP generating system, some may have envelopes

capsid

protected protein coat that protects nucleic acid of a virus, structure determined by viral nucleic acid accounts for mass of virus, make of capsomeres

capsomere

small protein subunits that make up capsids, could be several types of protein

envolope

combination of lipids, proteins, and carbohydrates that cover capsids, in some viruses not all,

spikes

carbohydrate protein complexes that protect from the surface of the envelope, covers envelops sometimes (not all envelopes have this), some viruses attach to host cells by this, projections

nucleic acids found in viruses

this classifies the virus along with structural differences, can be linear or circular, could also be seperated segments

name of viruses

genus—> virus, family —> viridae, other names —> ales

lab culture of viruses

cell culture cells suspended in solution (in continuous cell lines transformed into cancerous cells) infected cells detected via their deterioration (cytopathic effect), in living animals by injecting the virus into the egg viral growth is signaled by changed or death of the embryo

steps in multiplication of lytic bacteriophages T-even

attachment phage attaches by the tail fibers to host cell, penetration phage lysozyme opens cell wall tail sheath contracts to force the tail core and DNA into cell, biosynthesis production of phage DNA and proteins, maturation assembly of phage particles, release phage lysozyme breaks the cell wall

lysogenic cycle of bacteriophage lambda

phage dna incorporated into host cell dna, inserted prophage, when the host cell replicates its chromosome, it also replicated prophage DNA, results in phage conversion, specialized trnasduction

two factors that determine host range of a phage

requirements for its specific attachment to the host cells and availability within the potential host of cellular factors required for replication.

multiplication of bacteriophages

tail fibers attach to cell wall proteins, viral dna is injected into host cell, uncoating not required, biosynthesis in cytoplasm, lysogeny, host cell is lysed

multiplication of animal viruses

attachment sites are plasma (cell) mem. capsid enters by receptor mediated endocytosis or fusion, enzymatic removal of capsid proteins, biosynthesis: in nucleus (DNA viruses) or cytoplasm (RNA viruses) production of nucleic acid and proteins, maturation: nucleic acid and capsid proteins assemble, latency, slow viral infections, cancer, enveloped viruses bud out and release, nonenveloped viruses rupture plasma membrane

Describe seven events of multiplication of a DNA containing virus (Papovavirus)

attachment entry and uncoating DNA is released into nucleus of host cell —> transcription of a portion of viral DNA, then translation, products needed for multiplication, transcription is carried out by hosts transcriptase —>transcription and translation of late viral genes occur (capsid and other structural proteins) —> synthesis of capsid proteins in cytoplasm of host cells —> capsid protein migrate into nucleus of host cell, maturation occurs, viral DNA and capsid proteins assemble to form complete viruses —> complete virus then release from host cell

multiplication cycle of HIV retrovirus

RNA virus same as DNA virus replication but RNA viruses multiply in the host cells cytoplasm. Uses RNA dependent RNA polymerase that isn’t encoded in any cell genome but viral gene causes host cell to produce this enzyme

how can a virus induce cancer in a normal cell

10% of cancer, genetic material integrates into host cell’s DNA and replicates along host cells chromosomes, alters host cells characteristics. tumor cells go through transformation to acquire properties that are distinct from properties of uninfected cells.

Spongiform encephalopathies

mad cow disease (animal), Creutzfeldt-Jakob disease (humans), scrapie

viroids (& disease they cause)

short pieces of naked RNA, potato spindle tuber disease (virusoids are viroids enclosed in protein coat)

genome

genetic information in a cell

virion

complete fully developed infectious viral particle composed of nucleic acid and surrounded by protein coat outside a host cell, capsid, envelope, spikes

bacteriophage

viruses that can infect bacteria, grown in bacteria

prophage

inserted phage dna

specialized transduction

lysogenic cycle, specific bacterial genes transferred to another bacterium via a phage, changes genetic properties of the bacteria

provirus

ddss DNA mol. synthesized from viral RNA into host cells chromosomes, never comes out of chromosomes unlike prophage

lysozyme

digestive enzyme, active on major cell wall components and makes bacteria vulnerable to lysis

lysogen

bactera cell that contains an inactive bacteriophage ex: prophage

burst size

??

lysogenic conversion

host cells exhibits new properties due to prophage, can result in bacteria with virulence factors as toxins or capsules, bacterial cells is immune to infection by the same type of phage

lysogenic state (lysogen)

host cell remains alive, phage DNA is incorporated in the host DNA, phage conversion, specialized transduction

diphtheria toxin

von bering, causes diphtheria (effects mucous mem of nose and throat0, cytotoxin inhibits protein synthesis especially in nerve, heart, and kidney cells, corynebacterium diphtheriae

restriction enzymes

DNA cutting enzymes that exist in many bacteria

endonuclease

cut DNA backbone in a strand of DNA, facilitate repair and insertions

endocytosis

when a segment of the plasma membrane surrounds particle, or large molecule encloses it and brings it into the cell (phagocytosis, pinocytosis, and receptor mediated endocytosis)

Herpesviridae

double stranded dna, enveloped, simplexvirus (cold sores), varicellovirus (chickenpox), lymphocrytovirus (causes mononucleosis/mono), cytomegalovirus, roselovirus, rhadinovirus (causes kaposi’s sarcoma)

plaque

formed by bacteriophages, clearings on a lawn of bacteria on the surface of agar, each on expressed as pfu

plaque forming units (PFU)

used to express each plaque that corresponds to a single virus

prions

infectious proteins that are the cause of neurological diseases, proteinaceous infectious particles, inherited and transmissible by indigestion, transplant, and surgical instruments, (major problem is disinfection of surgical instruments), infected carcasses are incinerated sheep scrapie (animals scrape themself against fence until body is raw)

reverse transcriptase

makes DNA from RNA template (hepatitis b uses this)

protease inhibitor

cleaves lengthy precursor proteins into smaller mature structural proteins (capsid proteins) and functional proteins (enzymes), effective in HIV when paired with reverse transcriptase inhibitor

naked virus (nonenveloped)

only have a protein coat, more resistant to disinfectants and antiseptics

enveloped virus

roughly spherical, influenza or human herpes virus

lytic (virulent) phage

ends with lysis and death of host cell

latent infection

remain asymptomatic host cell for long periods, may reactivate (cold sores and shingles)

lysogeny

phage remains latent

latency

state where microbe persists a host without noticeable symptoms but can reactivate

Creutzfeldt-Jakob disease

rare, prion disease, fatal, brain proteins to misfold, TSE (transmissible spongiform encephalopathy) often in families, corneal transplants when accidental scalpel nicks of surgeon during autopsy, cases linked to growth hormones derived from human tissues, autoclaving instruments is not reliable unless at 134c and sodium hydroxide

Mad cow disease

bovine spongiform encephalopathy (BSE) caused by spontaneous mutations or supplements containing meat and bone from sheep who had scrapie

CWD chronic waste disease

prion disease, wild deer and elk in US and canada, fatal and might affect humans who eat infected livestock

DNA oncogenic virus

integrated into host cell DNA and induce tumors ex: papovavirdae, herpesviridae (epstein-barr virus)

animal virus

virus that infect animal cells

host range

the spectrum of host cells the virus can infect, 20nm-1000nm

latent

inactive

Papovaridae

ddss DNA non envolped, Papillomavirus (causes warts, can transform cells and cause cancer)

rna oncogenic viruses

retrovirdae (viral rna transcribed to dna using reverse transcriptase, can cause integrate into host dna) (HTLV-1, HTLV-2 cause adult T cell leukemia and lymphoma)

prion proteins

PrP^c: normal cellular prion protein, on cell surface, PrP^sc: scapie protein, accumulates in brain cells, forming plaques

Retroviridae

RNA, reverse transcriptase, viral enzyme copies viral RNA to make DNA in cytoplasm, DNA moves to nucleus. HIV