Chapter 13 - Virology and MOWs Flashcards
What is the type and name of the microbe that causes measles?
Virus
Measles morbillivirus
What is the shape and arrangement of the measles virus?
Spherical and enveloped
What is the type and name of the microbe that causes C. diff?
Bacteria
Clostridium difficile
What is the shape, endospore activity, and Gram result of the microbe that causes C. diff?
Rod shape
Forms endospores
Gram-positive
Is C. diff aerobic or anaerobic?
Anaerobic
What is the scientific name of athlete’s foot?
Tinea pedia
What is the type and name of the microbe that causes athlete’s foot?
Fungus
Trichophyton rubrum
What is the type of microbe that causes Creutzfeldt Jakob disease?
Prion - infectious proteins that cause brain proteins to misfold, leading to incurable neurological diseases and brain damage
What is the type and name of the microbe that causes rabies?
Virus
Lyssavirus
What is the shape, RNA makeup, and envelope status of the microbe that causes rabies?
Rod shape
Single-stranded RNA
- Negative-sense - has complementary RNA in it and needs to be transcribed so it can be positive-sense and be translated
Enveloped
What is the type and name of the microbe that causes HIV/AIDS?
Virus
Human immunodeficiency virus (HIV-1)
What is the shape, RNA makeup, and envelope status of HIV/AIDS?
Circular shape
Retrovirus - 2 copies of single-stranded RNA that is made into cDNA using reverse transcriptase when it is in a host cell
Enveloped
Are viruses alive?
No:
Lack cellular structure - only contain genetic material, protein coat, and sometimes an envelope - living organisms have cellular structure
Must reproduce inside a host cell - do not have the necessary organelles to go through replication, transcription, and translation withinin itself, so it must put genetic material in a host cell (parasitic)
Metabolism - have few or no enzymes for their own metabolism
What is a virus?
Small obligate intracellular parasites (must replicate in a host)
Made up of nucleic acid and capsid (protein)
What is host range?
The spectrum of host cells the virus can infect
How do viruses differ from bacteria (3)?
Structure:
- Bacteria have complex structures: cell wall, membrane, cytoplasm, genetic material in a nucleoid, outer structures like flagella and pili
- Viruses only have genetic material that is enclosed in a capsid; some have lipid envelope
Reproduction:
- Bacteria reproduce asexually through binary fission to produce 2 identical daughter cells
- Viruses replicate by inserting genetic material into a host cell, which is then incorporated and replicated within the host’s genome
Size:
- Bacteria are usually much larger than viruses
What is a virion?
A complete, fully developed, infectious viral particle composed of nucleic acid and surrounded by a capsid
What is a capsid?
A protein coat that surrounds and protects the nucleic acid of a virus
What is a capsomere?
Protein subunits that make up the capsid
What is an envelope?
A lipid, protein, and carbohydrate layer that covers the capsid
What are spikes?
Carbohydrate-protein complexes that project from the surface of the envelope
Means by which some viruses attach to host cells
What are nonenveloped viruses?
Viruses whose capsids aren’t covered by an envelope
What is the basic viral structure?
Composed of nucleic acid (single type) – either DNA or RNA
Surrounded by protein coat, called capsid
Some are enveloped
- If enveloped, can have spikes
What are the 4 morphologies of a virus?
Polyhedral
Helical
Complex
Enveloped
What is a helical shape?
Long rods
Rigid or flexible
Nucleic acid within a hollow, cylindrical capsid
Examples: rabies and Ebola viruses
What is a polyhedral shape?
Icosahedron - 20 triangle faces, 12 vertical corners, and 30 edges
Examples: adenovirus, Hep A, poliovirus
What is an enveloped shape?
Spherical
Enveloped helical or enveloped polyhedral
Examples: Marburgvirus and SARS-CoV-2
What is a complex shape?
Primarily bacteriophage
Capsids with additional structures - can have both helical and polyhedral parts (called binal)
Capsid, sheath, tail fibers, baseplate, pin
What suffix is used for genus names of viruses?
-virus
What suffix is sed for family names of viruses?
-viridae
What suffix is used for order names of viruses?
-virales
What is a viral species?
A group of viruses that share the same genetic information and ecological niche (host range)
What are the 3 ways a virus can enter a host?
Nonenveloped:
- Direct penetration - capsid binds to outside of cells to receptor; capsid is degraded and nucleic acid enters cell
Enveoped:
- Membrane fusion - envelope binds to surface and fuses to it because the plasma membrane of host is nearly the same as virus; nucleic acid is absorbed into cell
- Endocytosis - envelope binds to surface and host membrane surrounds virus and degrades it, releasing the nucleic acid
What are the 2 ways viruses are released from a host?
Lysing - make a bunch of new viruses (typically nonenveloped) until the cell explodes, releasing all of the viruses
Budding - virus is replicated and moves to the plasma membrane surface, pushes against host membrane until a bud forms, and is then released
What are the 3 parts of the one-step growth curve?
Eclipse period - immediate dip
- Entering into host cell and going through life cycle before being released
Virions released from host cell - steep upward climb
- Sickest/most dangerous time
Acute infection - peak of curve
- Highest number of virions
What are the steps of the lytic cycle for phages?
Attachement - phage attaches to host cell using surface proteins
Penetration - phage penetrates host cell and injects its DNA
Biosynthesis - phage nucleic acid is replicated and viral proteins including capsid and tail fibers are made
Maturation - viral components are assembled into virions
Release - Host cell lyses, and new virions are released
What are the steps of the lysogenic cycle for phages?
Attachement - phage attaches to host cell
Penetration - phage penetrates host cell and injects its DNA
Phage DNA integrates within the bacterial chromosome by recombination, becoming a prophage
Lyogenic bacterium reproduces normally (many cell division)
Prophage excises from the bacterial chromosome by another recombination event and enters the lytic cycle
What is the difference between the lytic and lysogenic cycles?
Lytic cycle ends with the lysis and death of the host cell, whereas the host cell remains alive and the virus lays dormant in the host’s genome in the lysogenic cycle
What are the steps for multiplication of animal viruses?
Attachment - Binds to host cell using surface proteins to bind to a specific protein receptor on host
Entry - Virus enters cell, often by receptor-mediated endocytosis
Uncoating - Separation of the viral nucleic acid from its protein coat
Biosynthesis - Viral nucleic acid is replicated and viral proteins including capsid and tail fibers are made
Maturation - Capsid proteins and nucleic acids are assembled into nucleocapsids
- If virus is enveloped, the envelope may be acquired as the nucleocapsid buds out from the cytoplasmic membrane
Release - Complete virions are released from the infected cell by lysis or budding
What are the steps for biosynthesis of DNA viruses?
Early genes are transcribed and translated in nucleus of host cell to produce enzymes needed for multiplication of viral DNA
Late viral genes are then transcribed and translated in host cell’s nucleus
Capsid proteins are synthesized in the cytoplasm of host cell
Cpasid proteins migrate into nucleus and maturation occurs - viral DNA and capsid proteins assemble to form complete virus
Complete viruses are released
What are the steps for biosynthesis of RNA viruses?
Virus multiplies in host cell’s cytoplasm using RNA-dependent RNA polymerase
ssRNA: + (sense) strand
Viral RNA serves as mRNA for protein synthesis
Steps:
- Transcription by viral RNA polymerase
- Translation of viral protiens, genome acts as mRNA
- Assembly
ssRNA: - (antisense) strand
Viral RNA is transcribed to a + strand to serve as mRNA for protein synthesis
Steps:
- Transcription by RNA-dependent RNA transcriptase
- Complementary +ssRNA to act as template and as mRNA
- Translation of viral proteins
- Assembly
dsRNA - double stranded
RNA makes up both strands
Steps
- Unwinding - 1 -ssRNA and 1 +ssRNA
- Transcription by viral RNA polymerase to make complementary RNA strands
- Translation of viral protein
- Assembly
Compare and contrast the multiplication cycle of a DNA and RNA-containing animal virus
Common steps: attachment, entry, uncoating, assembly, release
Differences:
- Replication site: DNA in nucleus; RNA in cytoplasm
- Genome replication: DNA uses host’s DNA polymerase and RNA polymerase; RNA uses own RNA-dependent RNA polymerase
What makes retroviruses unique among RNA viruses?
Single-stranded RNA produces DNA
Use reverse transcriptase to produce DNA from viral RNA genome
Viral DNA integrates into the host chromosome as a provirus
What is a provirus?
Viral DNA that is integrated into the host cell’s DNA
What is a retrovirus?
A type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades
List 5 DNA viruses
Adenovirus (common cold)
Poxviruses (smallpox and MPOX)
Herpesviruses (Chickenpox, mononucleosis)
Papovaviricetes (papillomas - warts)
Hepatitis B
How can RNA viruses differ from each other based on their genetic material?
Have different mRNA formation mechanisms depending on genetic material that is inserted into host cell
+ssRNA, -ssRNA, and dsRNA have different processes they go through before mRNA can be translated
List 4 RNA viruses
Coronaviruses (COVID-19)
Togavriuses (alphabirus- causes eastern equine encephalitis)
Rhabdoviruses (rabies)
Reoviruses
What is a prion?
An infectious protein that infects/degenerates the brain
What aspect of a prion makes it infectious?
Conversion of a normal host glycoprotein called PrPC into an infectious form called PrPSc
PrPC is involved in cell signaling, nerve function, and preventing apoptosis, so if it is altered to the PrPSc form, it is able to go through apoptosis and not perform its intended functions, leading to degeneration of the brain
What is an oncogene?
A proto-oncogene (encode proteins involved in stimulating normal cell growth) is mutated to trigger abnormal cell growth that can lead to cancer
What are oncogenic viruses?
Viruses that are capable of inducing tumors/ causing cancer
What are transformed cells?
Cells that acquire properites that are distinct from the properties of uninfected cells
After being transformed by viruses, tumor cells may contain a virus-specific antigen called TSTA
Tumor cells ungergo transformation - uncontrolled growth and lack of apoptosis
What are the advantages to viruses being small?
Can enter and exit host cells more easily
Can replicate quickly because they require fewer resources from host cell
Compact structure makes them more stable and resistant to environmental factors - can also evade immune system better
Why are some viruses small and others large?
Genetic complexity
Host range and specificity - those that infect more complex organisms may need to be larger and more complex themselves vs bacteriophages
How can viruses cause cancer?
Integrates genome into host to affect gene expression:
- Some interfere with tumor repression when they insert into host’s repressor gene - activates gene expression when it should be off
- Some carry copies of oncogenes as part of their genomes
- Some stimulate oncogenes already in the host (cellular proto-oncogene turns into oncogene)
What is an acute infection?
Short infection that goes away after a few days
Examples: flu, cold, COVID-19
What is a persistent infection?
Disease process that occurs over a long period of time (months to years)
Generally is fatal in the end - peaks at the end
Detectable throughout
Examples: HIV, subacute sclerosing panencephalitis (meales virus after a long time)
What is a latent infection?
Virus remains in asymptomatic host cell for long periods then can reactivate
Lays latent until something brings it out, such as a fever, sunburn, etc.
- Then it replicates and causes infection
Examples: herpes simplex virus
How does the influenza virus change so rapidly?
Has 8 segmented single stranded RNA genome
Reassortment and mutations
What is antigenic drift?
Minor to major changes in the form of one or both of the antigens on the viral surface - makes it more difficult for immune system to recognize them
RNA polymerase doesn’t have proofreading function so it incorporates a lot of mistakes, which mutates the strand when replicated
What is antigenic shift?
Radical changes in the form of one or both of the antigens on the viral surface - immune system cannot recognize virus
Occurs when 2 different strains of influenza virus infect a person and replicate
- When virus is packaged, it takes different pieces of either virus to form a new virus altogether
Why might the flu be so hard to immunize against?
Influenza virus is constantly changing because of antigenic drift and shift
Vaccine is targeted toward antigens on surface, and since these change every year with new flu strains, a new vaccine has to be developed
