BIOC20 MIDTERM EXAM QUESTIONS WITH
VERIFIED ANSWERS
Virion consists of - ANSWER -Nucleic acid genome
-protective protein coat
-Some contain a lipid envelope
Virion capsid - ANSWER Protective protein coat
Nature of Viruses - ANSWER Obligate intracellular parasites (only replicate in living cell)
Viruses lack - ANSWER Essential functions
-synthesis of basic biological building blocks (nucleotides, amino acids, CHO's, lipids)
-generation of ATP
-protein synthesis (ribosomes, tRNAs)
Uncoating - ANSWER First step, virus particles break down and release genomes inside
the cell
-released from protective protein shell
Once virus uncoats - ANSWER Genome can be used as a template for mRNA synthesis -
produce proteins
Newly made viral proteins - ANSWER Work together to replicate genome, encapsulate
the new genomes to form progeny virions
Virus morphology - ANSWER Distinct, genome sizes, and particle sizes
-smallest 20 nm in diameter, coding few as 2 proteins
-largest 500nm in diameter, coding > 1200 proteins
Virus genomes can be - ANSWER -RNA or DNA, not both
-single or double stranded
-circular or linear
Problem with RNA genome - ANSWER -no RNA polymerase - replication problem
-difficulty making RNA transcript
,Viruses can infect - ANSWER All forms of life, animals, plants, insects, bacteria, algae,,
fungi
Most abundant form of life - ANSWER Viruses, 10 fold excess of virus compared to
bacteria in earth oceans
Mass = 1 million blue whales
Length - 200 million light years
Study of viruses led to - ANSWER Identification of promoters for eukaryotic RNA
polymerase
Enzymes involved in cellular DNA replication
RNA splicing from studying viral mRNAs in eukaryotic cells
Isolation of numerous cellular oncogenes and the understanding that cancer is caused
by their mutation or unregulated expression
First virus discovered - ANSWER TMV
First virus discovered by - ANSWER Distinguished by filtration
Russian scientist Dimitri Ivanovski
Dutch scientist Martinus Beijerinck (first name for virus = contagious virus fluidium)
TMV - ANSWER Tobacco mosaic disease killing tobacco plants
Found by grounding up infected leaves trying to filter bacteria, passed through
porcelain filter was infecting leaves
Discovery about viruses in mid 1930s - ANSWER Highly purified TMV could form crystals
-challenged conventional notions about genes and nature of living organisms
Are virsuses alive? - ANSWER Not living entities, biochemical processes - only living
period inside host
1915-1917 scientist in England and France discovered bacteria - ANSWER Could be
listed by filterable agents
Study of bacteriophages helped establish the field of molecular biology by - ANSWER
Mapping phage genes
Elucidated phage replication cycles
Developed the plaque assay
Bacteriophage - ANSWER Viruses that infect bacteria
,Felix d'Herelle - ANSWER Worked on phage therapy
-using phage to treat human bacterial disease
-useful against antibiotic resistant bacteria
-use as antibacterial agents in humans is not accepted
Tumor virus study lead to - ANSWER Understanding of nature of cancer
-reverse transcriptase
-oncogenes
Now being used to construct vectors to express proteins to specifically destroy tumor
cells
Plaque assay allows for - ANSWER Quantitation of virus
-based on principle that bacteria diffract visible light, dense liquid cultures appear
'cloudy'
-bacteriophages lyes their host cell and this lysis causes a loss of diffraction, leading to
a clearing of bacterial culture ('clear lysis' = plaque)
Reported as PFU (plaque forming unit)
Method of virus detection and measurement - ANSWER Spread bacteria on surface of
nutrient agar (Petri dish) nd apply serial dilutions of a phage suspension
Occurs after serial dilutions of phage suspension to detect virus - ANSWER Phage binds
to bacterial cell -> replicates -> releases progeny phage particles -> taken up by
neighboring cells -> further replication rounds —-> visible plaque
Hemagglutination - ANSWER Convenient and rapid assay for many virus
Why hemagglutination is convenient - ANSWER RBC's easy to isolate and store, have
visible colour
Viruses often have many copies of receptor binding proteins on their surface, and RBCs
contain many copies of these receptors
Virus particles can be seen and counted by - ANSWER Election microscopy
-mix virus particles with electron dense stain, virus particles exclude the stain and show
up light against dark background (NEGATIVE STAINING)
Measurement of # of infections particles (plaque assay) compared to counts via electron
microscopy yields - ANSWER Ratio of Physical particles to infectious particles
Much greater than 1 (10, 100, 1000)
, Defective particles arise spontaneously - ANSWER Not all particles intact (enveloped
are sensitive)
Empty capsid (no genome present)
Defective genomes (mutations, missing part or strand)
Cellular anti-viral defenses
Viral replication cycle - ANSWER Single
-cells infected with an MOI (multiplicity of infection) of 10-100
-all cells infected simultaneously
-allows for synchronization of infection
Mouse polyomavirus replication cycle - ANSWER May not be detectable for -20 hours
(latent period)
Detailed pathway of virus replication - ANSWER Binding to receptor -> entry and
uncoating -> early gene expression -> replication of viral genome -> late gene
expression -> assembly of virions ->exit
Step 1 of virus replication cycle - ANSWER Virions bind to receptors on cell surface
-surface proteins of viruses bind CHOs of glycolipids and glycoproteins widely
distributed -> non specific binding
-some require specific proteins only on certain cell types -> high specific binding,
limiting virus tropism
- often a non-specific primary receptor, followed by a secondary receptor that is more
specific
Step 2 of virus replication cycle - ANSWER Virion (or viral genome) enters the cell
-Bacteriophage drills holes in cell membrane
-enveloped viruses fuse lipid envelope with plasma membrane
-endocytosis
Step 3 of virus replication cycle - ANSWER Early viral genes are expressed: Baltimore
VERIFIED ANSWERS
Virion consists of - ANSWER -Nucleic acid genome
-protective protein coat
-Some contain a lipid envelope
Virion capsid - ANSWER Protective protein coat
Nature of Viruses - ANSWER Obligate intracellular parasites (only replicate in living cell)
Viruses lack - ANSWER Essential functions
-synthesis of basic biological building blocks (nucleotides, amino acids, CHO's, lipids)
-generation of ATP
-protein synthesis (ribosomes, tRNAs)
Uncoating - ANSWER First step, virus particles break down and release genomes inside
the cell
-released from protective protein shell
Once virus uncoats - ANSWER Genome can be used as a template for mRNA synthesis -
produce proteins
Newly made viral proteins - ANSWER Work together to replicate genome, encapsulate
the new genomes to form progeny virions
Virus morphology - ANSWER Distinct, genome sizes, and particle sizes
-smallest 20 nm in diameter, coding few as 2 proteins
-largest 500nm in diameter, coding > 1200 proteins
Virus genomes can be - ANSWER -RNA or DNA, not both
-single or double stranded
-circular or linear
Problem with RNA genome - ANSWER -no RNA polymerase - replication problem
-difficulty making RNA transcript
,Viruses can infect - ANSWER All forms of life, animals, plants, insects, bacteria, algae,,
fungi
Most abundant form of life - ANSWER Viruses, 10 fold excess of virus compared to
bacteria in earth oceans
Mass = 1 million blue whales
Length - 200 million light years
Study of viruses led to - ANSWER Identification of promoters for eukaryotic RNA
polymerase
Enzymes involved in cellular DNA replication
RNA splicing from studying viral mRNAs in eukaryotic cells
Isolation of numerous cellular oncogenes and the understanding that cancer is caused
by their mutation or unregulated expression
First virus discovered - ANSWER TMV
First virus discovered by - ANSWER Distinguished by filtration
Russian scientist Dimitri Ivanovski
Dutch scientist Martinus Beijerinck (first name for virus = contagious virus fluidium)
TMV - ANSWER Tobacco mosaic disease killing tobacco plants
Found by grounding up infected leaves trying to filter bacteria, passed through
porcelain filter was infecting leaves
Discovery about viruses in mid 1930s - ANSWER Highly purified TMV could form crystals
-challenged conventional notions about genes and nature of living organisms
Are virsuses alive? - ANSWER Not living entities, biochemical processes - only living
period inside host
1915-1917 scientist in England and France discovered bacteria - ANSWER Could be
listed by filterable agents
Study of bacteriophages helped establish the field of molecular biology by - ANSWER
Mapping phage genes
Elucidated phage replication cycles
Developed the plaque assay
Bacteriophage - ANSWER Viruses that infect bacteria
,Felix d'Herelle - ANSWER Worked on phage therapy
-using phage to treat human bacterial disease
-useful against antibiotic resistant bacteria
-use as antibacterial agents in humans is not accepted
Tumor virus study lead to - ANSWER Understanding of nature of cancer
-reverse transcriptase
-oncogenes
Now being used to construct vectors to express proteins to specifically destroy tumor
cells
Plaque assay allows for - ANSWER Quantitation of virus
-based on principle that bacteria diffract visible light, dense liquid cultures appear
'cloudy'
-bacteriophages lyes their host cell and this lysis causes a loss of diffraction, leading to
a clearing of bacterial culture ('clear lysis' = plaque)
Reported as PFU (plaque forming unit)
Method of virus detection and measurement - ANSWER Spread bacteria on surface of
nutrient agar (Petri dish) nd apply serial dilutions of a phage suspension
Occurs after serial dilutions of phage suspension to detect virus - ANSWER Phage binds
to bacterial cell -> replicates -> releases progeny phage particles -> taken up by
neighboring cells -> further replication rounds —-> visible plaque
Hemagglutination - ANSWER Convenient and rapid assay for many virus
Why hemagglutination is convenient - ANSWER RBC's easy to isolate and store, have
visible colour
Viruses often have many copies of receptor binding proteins on their surface, and RBCs
contain many copies of these receptors
Virus particles can be seen and counted by - ANSWER Election microscopy
-mix virus particles with electron dense stain, virus particles exclude the stain and show
up light against dark background (NEGATIVE STAINING)
Measurement of # of infections particles (plaque assay) compared to counts via electron
microscopy yields - ANSWER Ratio of Physical particles to infectious particles
Much greater than 1 (10, 100, 1000)
, Defective particles arise spontaneously - ANSWER Not all particles intact (enveloped
are sensitive)
Empty capsid (no genome present)
Defective genomes (mutations, missing part or strand)
Cellular anti-viral defenses
Viral replication cycle - ANSWER Single
-cells infected with an MOI (multiplicity of infection) of 10-100
-all cells infected simultaneously
-allows for synchronization of infection
Mouse polyomavirus replication cycle - ANSWER May not be detectable for -20 hours
(latent period)
Detailed pathway of virus replication - ANSWER Binding to receptor -> entry and
uncoating -> early gene expression -> replication of viral genome -> late gene
expression -> assembly of virions ->exit
Step 1 of virus replication cycle - ANSWER Virions bind to receptors on cell surface
-surface proteins of viruses bind CHOs of glycolipids and glycoproteins widely
distributed -> non specific binding
-some require specific proteins only on certain cell types -> high specific binding,
limiting virus tropism
- often a non-specific primary receptor, followed by a secondary receptor that is more
specific
Step 2 of virus replication cycle - ANSWER Virion (or viral genome) enters the cell
-Bacteriophage drills holes in cell membrane
-enveloped viruses fuse lipid envelope with plasma membrane
-endocytosis
Step 3 of virus replication cycle - ANSWER Early viral genes are expressed: Baltimore
