Chapter 13 (viruses, viroids, & prions) Flashcards
Describe the general characteristics of viruses.
ACELLULAR: no cell membrane or organelles
GENONME: one or more pieces of DNA or RNA (never both)
PROTEIN COAT: “shell” around genome CAPSID
No ribosomes: cannot make proteins
No metabolism: no protein= no enzymatic pathway
must be inside host cell to replicate
No growth: viruses assembled using cell machinery
Define host cell specificity.
o How is it determined?
Describe viral genomes.
o 4 main types of nucleotides
o Linear vs. circular
o segmented vs. not
ALL viruses have genome & capsid
4 main types: dsDNA, ssDNA, dsRNA, ssRNA
(2 types of ssRNA: POSITIVE-just like mRNA translated by host ribosomes & NEGATIVE not recognized by ribosomes- converted to +ssRNA by using RNA-dependent RNA transcriptase (viral enzyme)
linear v. segmented are the genome shapes
segmented are many linear pieces
What is a capsid?
o Different types of capsids?
composed of subunits called capsomeres, protects genome, attachment to host cell (non enveloped viruses) & determines shape of virus
a) helical: capsomeres bound in a spiral tube
b) polyhedral: geodesic dome (soccer ball)
c) complex: capsomeres are many different shapes
What is a capsomere?
1 or more viral proteins
What is an envelope?
o Where does it come from?
not all viruses have envelope (naked viron & enveloped viron)
phospholipid membrane from host cell
contains viral proteins used for attachment (adhesins)-destroy envelope=destroy ability to infect host cells
Describe the 5 stages of lytic replication (causes host cell to lyse)
- ATTACHMENT (to host cell)
- ENTRY (of genome)
- SYNTHESIS (of genome copies & viral proteins)
- ASEMBLY (of above)
- RELEASE (occurs by lysis of cell)
Be able to describe the viral components, life cycle, host specificity for the following viruses:
bacteriophage: bacteria that infects bacteria
o bacteriophage T4
o bacteriophage lambda (what is lysogeny?)
BACTERIOPHAGE T4: GENOME: dsDNA: HOST E. coli: SHAPE: complex EXHIBITS: lytic replication of a virus
BACTERIOPHAGE LAMBDA: GENOME: dsDNA, HOST: E.coli, SHAPE: complex, EXHIBITS: lysogenic replication- a template phage (not always lead to lysis or cell)
LYSOGENY: remains a prophage until phage genome is induced, anything that damages DNA will induce the prophage to become active
Animal virus replication is “the same, but different” as bacteriophage replication. How so?
o direct penetration, membrane fusion, phagocytosis: describe and know which type of virus does which of these processes
o synthesis: where does transcription and translation happen for different virus types? What unique enzymes does each virus type need?
o Assembly: where? Nucleus vs. cytoplasm
o Release: lysis, exocytosis, budding: describe and know which type of virus does which of these processes
Same basic process 1) ATTACHMENT 2) ENTRY (3 methods) 3)SYNTHESIS 4)ASSEMBLY 5)RELEASE (3 options)
ENTRY: 1. direct penetration: naked viruses viral protein gets into host cell
2. Membrane fusion: enveloped viruses capsid & genome released into cell
3. Phagocytosis: enveloped & naked viruses, binding to receptors on cell surface triggers the cell to ENGULF the virus (fuse of membranes)
SYNTHESIS: DNA viruses- replication, transcription, translation just like in HOST CELL
RNA viruses +ssRNA genome is used for protein synthesis, -ssRNA genome not recognized by ribosome need RNA dependent RNA transcriptase, REtrovirus genome is converted to DNA; replication of the genome uses DNA template; transcription & translation for viral proteins
ASSEMBLY: DNA assembled in NUCLEUS
RNA assembled in CYTOPLASM
RELEASE: NAKED VIRUSES 1. lyse cell (burst)= kill host cell
2. exocytosis =host cell lives
ENVELOPED VIRUSES 3. release by budding (doesn’t kill cell) virus sheds over period of time: persistent infection
For all the viruses listed below, you should be able to describe the viral components, life cycle (including target host cell), and the characteristics of the diseases they cause. Reminders of additional details are below each virus:
o Human Papilloma Virus
how does it cause cancer?
GENOME: dsDNA
HOST CELL: stem cells from epidermis
TRANSMISSION: direct contact & indirect contact
CAUSES: many types of warts
HPV can be latent → incorporates its genome into the host cell genome
TUMOR= cells dividing inappropriately
MALIGNANT TUMOR (cancer)= tumor that has spread to other tissue (metastasis) & produces new tumors
A normal state would be to have a protooncogene (protein that tells cell to divide) & gene repressor (prevents over expression)
when take the first hit it affects the protooncogene now cells divide uncontrollably but gene repress prevents from signal to be expressed
Second hit disrupts the gene repressor which then oncogene expressed more cause tumor that leads to cancer
o For all the viruses listed below, you should be able to describe the viral components, life cycle (including target host cell), and the characteristics of the diseases they cause. Reminders of additional details are below each virus:
o Influenza virus
Describe: antigenic shift and antigenic drift
Connections: Flu, antigenic drift, antigenic shift & pandemics?
GENOME: -ssRNA in 8 segments (ea. segment surrounded by own capsid)
ENVELOPED VIRUS: must have all 8 segments to be functional
HOST CELL: cells of respiratory tract (seasonal upper resp tract & serious lower resp. tract)
TRANSMISSION: droplet
Hemagglutinin (HA) & Neuraminidase (NA) allow virus to attach to host cell
mutations occur frequently b/c there isn’t a proofreading enzyme &
-ssRNA uses an RNA dependent RNA transcriptase to copy genome (turn into +ssRNA)
mutations in genome →changes protein → changes HA& NA→ new to our immune system ( ANTIGENIC DRIFT- small changes in a single strain’s viral genome immune system don’t recognize antigens)
serious flu strains occur by ANTIGENIC SHIFT- combination of 2 different viral genomes examples would be BIRD FLU (H5N1) serios 60% infected people die not a pandemic b/c can’t easily infect people
SWINE FLU: 7% of infected people died IS a pandemic very good at infecting people
o For all the viruses listed below, you should be able to describe the viral components, life cycle (including target host cell), and the characteristics of the diseases they cause. Reminders of additional details are below each virus:
o Human Immunodeficiency Virus
integrase; reverse transcriptase; protease
treatments & prevention?
GENOME: +ssRNA; a retrovirus
HOST CELL: human helper T cells( killing of bad cells)
TRANSMISSION: contact w/bodily fluid, sexual contact, injected drugs, blood transfusion, prenatal
CAUSES: attacks immune cells in humans (T helper cells)
1. attachment of HIV to host cell (t helper) by connecting to glycoprotein
2. cell enters by phagocytosis 3. virus released uncoating of capsid
4. REVERSE TRANSCRIPTASE copy complementary +ssRNA & makes -ssRNA makes copy of dsDNA (b/c retrovirus)
5. dsDNA gets transported to nucleus
6. INGEGRAE clips host cell chromosome & insert virus
7. viral DNA transcribed copies can be used as mRNA
8. viral proteins made 9. Virus buds off release attachment
10. PROTEASE clip 2 proteins apart & allows everything to fully assembly
TREATMENT: antiviral “cocktail” (to avoid resistance) VACCINES HIV changes too quickly → antigens not stable
o For all the viruses listed below, you should be able to describe the viral components, life cycle (including target host cell), and the characteristics of the diseases they cause. Reminders of additional details are below each virus:
o Coronaviruses
Which coronaviruses infect humans?
Why are RNA viruses usually more successful than DNA viruses?
How are coronaviruses different to other RNA viruses?
* What’s the connection between slow mutation rate and human health?
o SARS-CoV-2
Describe the structure of the SARS-CoV-2 virus.
* Based on your knowledge of the genome and structure of the SARS-CoV-2, describe its replication cycle.
* List the mechanisms of transmission of SARS-CoV-2
Describe the signs and symptoms of COVID-19.
* “Long haulers”?
GENOME: +ssRNA w/helical capsid
HOST CELL: Glycoprotein spike for adhesion
TRANSMISSION:
CAUSES:
RNA viruses have no proofreading ability means they replicate anf the more they mutate. The more they mutate the more possibility of different strains that can infect new host (antigenic drift)
SARS-CoV-2 enveloped (entry membrane fusion or endocytosis) (release-budding) S-protein is the adhesion, Target receptor: ACE2 sound on many tissues of human body
Typical symptoms: fever, cough, headache, fatigue, loss of smell
Severe symptoms: SOB, hypoxia
Long haulers: fatigue, headaches, loss of smell, muscle weakness
What is a viroid?
o What type of organisms do viroids infect?
o What kind of genome does it have?
a small loop of RNA that infects plant cells
RNA with no capsid
What is a prion?
o name a disease it causes
o How do prions cause disease?
an infectious protein
disease cause: kuru, creutzfeld-jakob disease, “mad cow”
prion Prp protein a normal nervous tissue protein; can stably fold two ways
