Virology test 1 review Flashcards

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NOT living

not cells (no nucleus, organelles, cytoplasm)

subcellular infectious agents

and

obligate intracellular parasites

• must be in cell to function

complex nucleoprotein particle

doesnt do anything outside the cell

other unicellular organisms, some bacteial species, some protozoa can multiply only inside other host cells

can have EITHER

• DNA
• OR
• RNA

NEVER BOTH!!!

synth. subunits (proteins), then assemble the virus

(very distinct from other things, like bacteria can do fission, etc.)

NO

NO

energy or proteins

filterable agents

obligate intracellular parasites

viral components assembled

genome can be DNA OR RNA (never both)

morphology: naked capsid OR envelope

• viruses not living
• must be infectious to endure in nature
• must be able to utilize host cell processes to make their components (mRNA, protein, copies of their genomes, etc.)
• must already have/encode for processes that the cell doesnt provide
• viral components must self assemble

• realized that infectious diseases were transmitted by air, water, food, or close contact to sick ppl caused by mysterious elements in fluids called virus
• had ppl w rabies and didnt know what it was
• had ppl w polio and didnt know what it was

no clear understanding of the nature of these disease agents, which are know now as viruses

• didnt understand, just know some things were working

• showed that agent that caused tobacco mosaic disease could passn through fine earth or porcelain filters which retain bacteria
• VIRUSES WERE FIRST DISTINGUISHED FROM OTHER MICROORGANISMS BY FILTRATION

experiments established that certain infectious agents are much smaller than bacteria - called filterable viruses

• 1st tumor virus (RVS, rous sarcoma virus) isolated from sarcomas of chicken in 1911
• years later -> RSV recognized as representative of retrovirus family
• RSV virus which existance of oncogenes was discovered
• wendell stanley found that purified tobacco mosaic virus could form crystals
  • shocked scientific world bc placed viruses at edge btw living organisms and chemical compounds
  • posed question: are viruses living or inanimate???
• CRYSTALLIZATION OF TOBACCO MOSAIC VIRUS CHALLENGED CONVENTIONAL NOTIONS ABOUT GENES AND NATURE OF LIVING ORGANISMS
• Show many properties of life ONLY when inside cell (given means to support replication) because they have ability to mutate, evolve, etc

• they do share many properties of life:
  • ability to mutate, evolve, reproduce themselves when enter cells that support their replication
• stanley and others showed that viruses contain both protein and nucleic acids
• at the time, it was still not known that genes were made up of nucleic acids
• dev of electron microscope allowed scientists to see viruses for first time (1930s)

see pic

• nucleic acid - DNA or RNA
• capsid
• nucleocapsid - capsid + nucleic acid core
• envelope
• capsomer

capsid + nucleic acid core

nucleocapsid

• DNA/RNA
• proteins

• nucleocapsid
• glycoproteins and membrane

• DNA -> RNA -> PROTEIN
• RNA -> DNA in viruses that use reverse transriptase
  • DNA from RNA to make more RNA

• single vs double stranded
• segmented vs nonsegmented
• linear vs circular
• positive vs negative stranded vs ambisense

DNA dependent

• DNA polymerase
• RNA polymerase

RNA dependent

• RNA polymerase
• DNA polymerase

viral encoded vs carried in the vial particle

• if virus codes for it, or if it carries it

lack complete genome

= cannot replicate completely/cannot form protein coat

failed infections of a cell

replication of a particular type / strain of virus

biosynthetic machinery to support the complete replicative cycle of the virus

2 types symmetry present in capsids

1. cubic symmetry (icosahedron)
2. helical symmetry
3. neither - ex: poxvirus

icosahedron

• circles inside = nucleic acid
• circles outside = capsomeres that cover and give helical configuration
• for viruses that infect HUMANS
• all these have OUTER ENVELOPE

protomers (= cleaved long proteins made by virus)

they are assembled into pentamers (capsomers)

= how get mature virus form

naked virus = nucleocapsid

enveloped virus = nucleocapsid, AND:

• structural protein = matrix protein
  • only thing inside
• lipid bilayer (outer membrane from host cell)
• glycoprotein - in order to have receptor proteins

• only protein structure

stable to:

• temp
• acid
• proteases
• detergents
• drying

release from cell by lysis

• spread easily (on fomites, hand-hand, droplets, etc.)
• dry out + retain infectivity
• survives gut
• resistant to detergents + bad sewage treatment
• can elicit protective antibody response

lysis

• proteins
• membrane
• lipids
• glycoproteins

disturbed by:

• acid
• detergent
• drying
• heat

modifies cell membrane during replication

budding and cell lysis

• bc use membrane of host cell

• must stay wet
• cannot survive GI tract
• spreads in large droplets, secretions, organ/blood transplants
• doesnt need to kill cell (budding)
• initiate cell mediate immune response
• pathogenesis often bc of hypersensitivity and inflammation due to cell mediated immunity

• viroids - are only RNA
• prions - are only protein

smaller than viruses

smallest known pathogens

naked, circular, ssRNA - dont encode protein

only infect plants

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animal cell culture

1. characteristics of animal cell culture
2. growth factors
3. cell cycle
4. cell transformation and elements of cancer

...

their in vivo tissues/environments

in vitro (on glass)

taking cells from their natural setting, characterizing their growth and functional properties, and keeping them in culture so that they are readily available for experimentation

• start w/ animal cell culture
• culturing is taking cells from vivo environment to conditions in another place they can grow (in vitro)

cells grown in culture provide more homogenous population of cells from which to extract material, and they are also much more convenient to work with in the lab (in sterile plasticware)

cells directly from animals/humans

(extracting primary cells from them)

In vitro literally translates from Latin as “in glass.” These methods involve experimenting with cells outside a living organism. The original reference to glass is quite literal since in vitro experiments were historically conducted in Petri dishes or test tubes, made of glass.

In vitro cultured cells are purified and isolated from their natural biological environment.

(google)

Ex vivo literally translates from Latin as “out of the living.” In these experiments, living tissues are directly taken from a living organism and immediately studied in a laboratory setting with minimal alterations to the organism’s natural conditions. An example of this is the use of human skin explants derived from surgical procedures.

google

these investigations refer to experiments in live animals (NOT in cell cultures)

when conducted in humans = clinical (translational) research

studying animal as a whole

isolated from INTACT TISSUE where they live in body

• disrupt ECM and cell-cell junctions that hold cells together
  • treat w/ proteolytic enzymes (trypsin, collagenase) = digest + destroy proteins in ECM
  • treat w/ agents as EDTA that bind Calcium ions that cell-cell adhesion depends on
  • tissue can be separated into single cells by agitation

cells can be separated from a mixed cell suspension

• most general cell separation techniques: use antibodies coupled to flourescent dyes/magnetic beads = label specific cells (cell sorting)
• antibody - molecule produced by B lymphocyte, specifically recognizes certain structures of other molecules (antigens)

• cell culture established from organs/tissue
• eventually die
  • hayflick limit - limit of division of about 50-70 times
  • experience senescence and death

• replication capacity of a cell before experiencing senescence and death
• 50-70 divisions
• only occurs in differentiated cells (stem cells can continue to divide)
• this occurs in our bodies as well

progressive shortening of telomeres (with each cell division)

repetitive DNA caps at end of each chromosome

elongates telomeres, which are shortened after each cell division

cells stop making telomerase, which is why their telomeres shorten with each division -> leading to eventual senescence and death of the cell

telomerase continuously

since they express it, their telomeres do not shorten, and thus, cancer cells are immortal

senescence

• cells stop proliferation at hayflick limit after certain number divisions
• if they remain normal cells, senescence will occur
• cell strain
• euploid
• before senescence is reached, cells may be changed by viruses, carcinogens, etc or spontaneous transformation -> cell line

euploid (normal # chromosomes) population of cells

• cell line
• aneuploid (abnormal # chromosomes or changed chromosomes)
• occurs if primary cells (normal cells) undergo transformation into abnormal ones
• can be cultured indefinitely due to telomerase continuation

aneuploid (abnormal # or changed chromosomes)

can culture indefinitely bc of telomerase activity continuation, do not die

normal cells can turn into abnormal cells (cell line) by carcinogens, transforming viruses, spontaneous transformation, etc.

• line of cells derived from the cell lines
• in vitro characteristics of tumor cells (foci)
• can turn into these bc of carcinogens, etc. (stated before)

cell line derived from primary tumor cells (ex vivo tumor cells, from an organism)

without attaching to a surface and proliferates to much higher density in a culture dish

transformed cell line

tumors in mice

carcinogenic

short and long term test for genotoxicity and carcinogenicity (transformation test)

see pic

• must resemble blood plasma, so has things to make it as similar as possible
  • amino acids, vitamins, glucose, buffers, serum, antibiotics, etc. additives

all animal cells in culture derived from animal tissue

• adherent vs suspension

cell types

1. primary cells - eventually stop replicating
2. continuous cell lines
   • transformed/tumor/spont. altered cells
   • stem cells

stem cells (self renewing) cultured in vitro and can be propagated indefinitely

derived from either animal or human tissues and come from 1 of 3 sources

• embryonic stem cells
• adult stem cells
• induced stem cells

• euploid
• high serum conc.
• finite lifespan/hayflick limit
• display properties of differentiated cells
• respond to modulators of cell growth (growth factor, inhibitor, etc)
• do NOT produce tumors
• adherent cells - need contact with solid surface for division (anchorage dependent growth)
• subject to contact inhibition - stop growing when touch neighbor cell, grow again when have space

• aneuploid
• may have anchorage independent growth
  • dont need to be anchored to duplicate
• immortal - divide forever bc telomerase
• do not respond to neighboring cells - no contact inhibition
• dont display properties of differentiated cells
• do not respond to modulators of cell growth

exert modifications on cells

• cytopathic (cytolytic) viruses
  • kill their host cells (lysis)
  • either completely eliminated by immune system or kill infected organism (lysis)
• noncytopathic viruses (LCMV)
  • propagate without killing their host cells
  • leave cell via other mechanisms
• persistent virus
  • ex: herpes virus, chickenpox, shingles
  • lytic/latent life cycle
  • CANNOT be cured of this virus
    • virus hides until immunosuppression, then comes out
  • cytopathic or cytopathogenic effects (changes in host cell caused by viral invasion)
    • change morphology
    • apoptosis
    • necrosis
    • cell fusion (syncytia)
    • hemagglutination
    • change in growth or lifespan
    • oncogenic transformation

• kill their host cells (lysis)
• either completely eliminated by immune system or kill infected organism (lysis)

• propagate without killing their host cells
• leave cell via other mechanisms

• ex: herpes virus, chickenpox, shingles
• lytic/latent life cycle
• CANNOT be cured of this virus
  • virus hides until immunosuppression, then comes out

active, programmed process of autonomous cellular dismantling occurring in a cell, that avoids eliciting inflammation

passive, accidental cell death of a group of cells resulting from environmental pertubations with uncontrolled release of inflammatory cellular contents

...

viral proteins that mediates fusion of an infected cell with neighboring cell

• lead to formation of multinucleate cells - syncytia

virus w/ this puts molecules on surface that cause fusion of cell w/ neighboring cell

ex: flu, COVID, syncytium resp. virus

rxn that causes clumping of RBC in presence of some enveloped virus

glycoprotein on viral surface (hemagglutinin) interacts w/ RBCs leading to clumping of RBCs

virus attach to RBC and agglutinate

ex: flu

tumors

is a transforming virus

which are cells that can replicate?

• in vivo - in embryo and adults
  • embryo - embryonal cells, stem cells
    • pluripotent - undifferentiated, can become any cell type
  • adult - adult stem cells
    • multipotent - restricted to become any type of cell in the tissue/organ they reside (bone marrow, fat, brain, blood vessels, skin, teeth, heart, liver)
    • adult stem cells replace cells lost in tissue as needed (ex: skin growth every day)
  • benign + malignant (cancer) tumor cells
• telomerase expressed/activate in tightly controlled + regulated fashion, except in malignant cells where it is cont. expressed/activated and they are then immortal

Embryo stem cells - Pluripotent – undifferentiated, can become any type of cell

Adult stem cells – multipotent

- replace cells lost in tissue/organ they reside as needed

Benign and malignant tumor cells

- tumor cells can be benign – have capacity to replicate, but do not metastasize and invade

- telomerase expressed regulated/controlled

now in vitro:

• primary cells - limited capacity: hayflick limit, telomers shorten progressively, senescence, death
• telomerase continuously expressed/activated enabling cell immortality in the following:
  • spontaneous generated cell lines
  • transformed cell lines
  • tumor (cancer) cell lines

telomerase - (an enzyme) is a ribonucleoprotein complex

• catalytic core: telomerase reverse transcriptase (TERT)
• noncoding human telomerase RNA (hTR) which serves as template for the addition of telomeric repeats to chromosome ends

endogenous and exogenous stresses, including telomere dysfunction

also to oncogene activation, tumor suppressor genes inactivation, oxidative stress, mitochondrial dysfunction, and persistent DNA damage

• cellular, tissue, organ, and body levels
• related to the aging process

inflammatory

part 2 of lecture

• secreted proteins which exert their effects at very low concentrations (1-^-9 to 10^-11 M)
• regulate protein synthesis and cell growth
• act on cells that express specific receptors
• can stimulate or inhibit proliferation or differentiation
• over 60 known growth factors
  • broad specificity
  • narrow specificity

growth factors = proteins

the main growth factors

dont need to memorize

produced by diff cell types

macrophages make most types of growth factors

Growth factors act on specific receptors

- end: give info in nucleus for cell to express certain thing

Interact w/ receptor -> phosphorylate -> kinases activated/phosphorylated

• Kinases go to nucleus -> activate gene/regulatory proteins
• Genes have to do w/ expression, regulation etc.

• autocrine
• across gap junctions
• paracrine
• endocrine

• cell targets itself
• signaling acts on the signaling cell
• 1 cell produce growth factor that goes back to interact w/ growth factor on same cell that produced it
• Bc only way to induce this function, must go out and activate the cell signaling pathway

• cell targets a cell connected by gap junctions
• signaling molecules moving directly between adjacent cells
• internal receptors found in cell cytoplasm
• bind ligand molecules that cross the plasma membrane

• a cell targets a nearby cell
• signaling act on nearby cells
• Growth factor act on receptor in neighbor cell

• a cell targets a distant cell through the bloodstream
• signaling uses the circulatory system transport ligands

part 3

1. the cell cycle, or cell division cycle, is the series of events that take place in a cell leading to its division and duplication (replication)
2. cell cycle can be divided in 2 periods
• interphase
• cell growth
• mitosis
• cell division into 2 daughter cells
3. cell cycle consists of four distinct phases
• interphase

1. G1 phase
2. S phase
3. G2 phase

• 4. M (mitosis)

• interphase
• cell growth
• mitosis
• cell division into 2 daughter cells

• interphase

1. G1 phase
2. S phase
3. G2 phase

• 4. M (mitosis)

• checkpoints used by cell to monitor + regulate progress of the cell cycle
• checkpoints
• G1 - ensure ready for DNA synthesis
• G2 checkpoint - ensure ready to enter M phase and divide
• if not, mitosis avoided
• metaphase checkpoint - ensure cell ready to complete cell division
• chromosomes aligned?

due to serum deprivation of the proliferating cell in culture -> arrest and into G0 state

protein synth. rate decreases to 20%

cannot pass G1 checkpoint/go into G1

• process by which cells in a culture at diff stages of cell cycle are brought to the same phase
• vital for cell study -> population-wide data

1. physical fractionalization
2. chemical blockade

1. serum starvation
2. chemically
   • nocodazole - arrest at metaphase
   • hydroxyurea - block in S phase
   • mimosine - late G1 arrest

Generation of transformed cells (mechanisms of cell transformation)

• culturing of primary cells for long periods (rodent cells)
• mutagenesis (genotoxic chemical compounds or other means)
• mutagens can transform the cells
• tumor viruses (HTLV-1)
• viruses can transform the cells
• transfection with oncogenes
• oncogenes can be responsible for inducing cancer
• can be isolated from tumors (= tumor cells)

• as occurring in any cell w/ initiating first mutation in any gene relevant to cancer
• malignant cell transformation can be achieved by tumor viruses, chemical carcinogens, etc.

- initiation - initiated cell

-> cell proliferation

-> promotion (altered cell foci prenoplastic lesion)

-> genomic instability and increased cell proliferation (addl genotoxic and promoting carcinogens)
-> progression (invasion and metastasis) = cancer

= carcinogenesis somatic mutation theory model

Model of cancer genesis

Malignant transformation – initiation – when cell turns cancer

Cancer progress through years from 1st cell’s initiation

Initiated cell can be repaired by DNA repair mechanism

- if DNA mutation remains, then another body system finds the cell and eliminates it

- if still have tumor cell, then these two systems failed to eliminate it

- then cell will proliferate -> become tumor

- progression – when benign tumor has a cell that then invades blood vessel and metastasizes

• as occurring in any cell w/ initiating first mutation in any gene relevant to cancer
• malignant cell transformation can be achieved by tumor viruses, chemical carcinogens, etc.

• immortalization
• aberrant growth control
• loss of contact inhibition
• anchorage independence (colony formation in soft agar)
• tumorigenicity (tumor formation in animals)
• malignancy (formation of an invasive tumor in vivo)

note: transformation is a multistep process, and varying degrees of transformation are measurable

• growth signals
• self-sufficiency in growth signals
• dont need info from growth factors
• insensitivity to anti-growth signals
• cell division
• limitless potential for cellular replication
• escape from apoptosis
• oncogenesis
• tissue invasion and metastasis

cancer cannot be described in vitro, but only in vivo (invasion and metastasis)

Diagnosis in cancer can ONLY be done by a biopsy – shows invasion + metastasis

- invasion when a cell of the benign tumor breaks the yellow membrane and goes into extracellular matrix and into blood

cancer cannot be described in vitro, but only in vivo

invasion and metastasis

Diagnosis in cancer can ONLY be done by a biopsy – shows invasion + metastasis

- invasion when a cell of the benign tumor breaks the yellow membrane and goes into extracellular matrix and into blood

• oncogenes
• tumor suppressor genes

NORMAL genes in a genome

normal cells that stimulate cell growth and division

Proto-oncogenes are genes that normally help cells grow and divide to make new cells, or to help cells stay alive.

ex: growth factors, mitogens, receptor tyrosine kinases, serine-theronine kinases, GTPases, transc. factors, etc.

When a proto-oncogene mutates (changes) or there are too many copies of it, it can become turned on (activated) when it is not supposed to be, at which point it's now called an oncogene.

cause cancer thru gain of function

one of main characteristics of cancer - uncontrolled growth

causes transformation of normal cells into tumor cells

can activate by diff mechanisms (mutagenesis, amplification, mutations, chromosomal translocations, etc.)

ex: Ras, HER2, Myc, Cyclin D

oncogene

gained function

• important regulators of biologic processes
• do NOT reside in genome for purpose of promoting tumors
• they are normal biologic process
• play role in cell growth (proliferation, apoptosis, genome stability, differentiation, etc.)
• causes transformation of normal cells into tumor cells

(see pic)

ex:

• tyrosine -> abl oncogene -> cause sarcoma in cat
• serine/threonine -> raf oncogene -> cause sarcoma in chicken/mouse
• etc.

diff functions of growth factors

• all are proto-oncogenic functions required by healthy cell to function
• if any activated -> then have an oncogene

• provide negative control of cell proliferation in normal genes
• loss of function of proteins encoded by these genes liberated cell from growth constraints -> contributes to malignant control
• are BRAKES in proliferation of cells
• both copies of tumor suppressor gene must be mutated/lost to result in loss of growth control
• they are recessive genes
• ex: Rb, p53, BRCA1/2

• deletion
• point mutation
• mutation followed by duplication
• loss of heterozygosity (LOH)
• DNA methylation
• post-transc. mech-bindind to DNA viral oncoproteins
• epigenetic silencing

• oncogenes - accelerators
  • 1 mutated is enough for excessive cell proliferation
• tumor suppressor - brakes
  • BOTH genes must be inactivated to yield excessive cell proliferation

cervical carcinoma

liver cancer

burkitt's lymphoma

kaposi's sarcoma

liver cancer

adult T cell leukemia