MICROBIOLOGY 2215 CSCC EXAM SCRIPT
TESTED QUESTIONS FULL SOLUTION
PREMIUM STUDY MATERIAL
●● General Characteristics of Viruses
Answer: Non-living entities
Not considered organisms (they cannot exist independently from the
host cell)
Can infect organisms of every domain
Cannot multiply unless they invade a specific host cell and instruct its
genetic and metabolic machinery to make and release new viruses
Commonly referred to by organism they infect
Animal viruses, Plant viruses, Bacteriophage
●● Virus Architecture
Answer: Virus particle called virion consists of nucleic acid surrounded
by protein coat
Protein coat termed capsid composed of capsomers
Virus capsid shapes: Isometric, Helical, Complex
Virion: Enveloped - surrounded by lipid membrane or Naked - without
envelope
●● Viral genome
,Answer: Contains only single type of nucleic acid
Either DNA or RNA
NEVER BOTH
Can be linear or circular
Single-stranded or double- stranded
●● Virus replication cycle overview
Answer: Only multiply inside metabolizing cell
Use host machinery to support reproduction
Every virus contains information to make viral proteins, assure
replication and move in and out of host cells
Viruses live in two phases
Extracellular phase = Metabolically inert
Intracellular phase = Metabolically active
●● Interactions with host cells
Answer: Some multiply inside cell, producing numerous progeny =
Termed productive cycle
Lytic cycle = virus lyse infected cell
Some integrate into host genome
Termed latent cycle = Lysogenic state
,●● Virus adsorption/attachment
Answer: The virus and host cell collide by chance
The base plate of a phage with its tail spikes settles on the surface of the
bacterium or viral spikes settle on host cell receptors
●● Penetration - Entrance of the virus OR its nucleic acid in the host cell
Answer: Plant viruses and bacteriophage inject the nucleic acid into the
host through the cell wall
Animal viruses enter the cell whole then uncoat to reveal the nucleic
acid
Animal cells have no rigid cell wall
●● Virus Assembly (or maturation)
Answer: This stage is the assembling of the replicated viral components
into an intact, mature virus
The protein structures of the phage such as the tail, heads, and tails
(sheaths), tail spikes and tail fibers are synthesized independently of one
another
●● Virus release
, Answer: Host cell bursts (lyses) and releases viruses to the outside
environment
Viruses are now extracellular
As viruses leave the host cell, the envelope is picked up, this is called
budding
The envelope is made of a portion of the host cell plasma membrane
which becomes the lipid envelope of the virus
●● Virus Lysogeny (Latency)
Answer: Some viruses will cause both lytic cycles and lysogenic cycles
depending on external conditions
Replication of a temperate virus
This is a non-productive cycle
Lysogeny begins like the lytic cycle
Adsorption
Penetration, then
Incorporation
●● Virus lysogeny incorporation
Answer: Viral nucleic acid incorporates onto the host chromosome
This virus is called a prophage
TESTED QUESTIONS FULL SOLUTION
PREMIUM STUDY MATERIAL
●● General Characteristics of Viruses
Answer: Non-living entities
Not considered organisms (they cannot exist independently from the
host cell)
Can infect organisms of every domain
Cannot multiply unless they invade a specific host cell and instruct its
genetic and metabolic machinery to make and release new viruses
Commonly referred to by organism they infect
Animal viruses, Plant viruses, Bacteriophage
●● Virus Architecture
Answer: Virus particle called virion consists of nucleic acid surrounded
by protein coat
Protein coat termed capsid composed of capsomers
Virus capsid shapes: Isometric, Helical, Complex
Virion: Enveloped - surrounded by lipid membrane or Naked - without
envelope
●● Viral genome
,Answer: Contains only single type of nucleic acid
Either DNA or RNA
NEVER BOTH
Can be linear or circular
Single-stranded or double- stranded
●● Virus replication cycle overview
Answer: Only multiply inside metabolizing cell
Use host machinery to support reproduction
Every virus contains information to make viral proteins, assure
replication and move in and out of host cells
Viruses live in two phases
Extracellular phase = Metabolically inert
Intracellular phase = Metabolically active
●● Interactions with host cells
Answer: Some multiply inside cell, producing numerous progeny =
Termed productive cycle
Lytic cycle = virus lyse infected cell
Some integrate into host genome
Termed latent cycle = Lysogenic state
,●● Virus adsorption/attachment
Answer: The virus and host cell collide by chance
The base plate of a phage with its tail spikes settles on the surface of the
bacterium or viral spikes settle on host cell receptors
●● Penetration - Entrance of the virus OR its nucleic acid in the host cell
Answer: Plant viruses and bacteriophage inject the nucleic acid into the
host through the cell wall
Animal viruses enter the cell whole then uncoat to reveal the nucleic
acid
Animal cells have no rigid cell wall
●● Virus Assembly (or maturation)
Answer: This stage is the assembling of the replicated viral components
into an intact, mature virus
The protein structures of the phage such as the tail, heads, and tails
(sheaths), tail spikes and tail fibers are synthesized independently of one
another
●● Virus release
, Answer: Host cell bursts (lyses) and releases viruses to the outside
environment
Viruses are now extracellular
As viruses leave the host cell, the envelope is picked up, this is called
budding
The envelope is made of a portion of the host cell plasma membrane
which becomes the lipid envelope of the virus
●● Virus Lysogeny (Latency)
Answer: Some viruses will cause both lytic cycles and lysogenic cycles
depending on external conditions
Replication of a temperate virus
This is a non-productive cycle
Lysogeny begins like the lytic cycle
Adsorption
Penetration, then
Incorporation
●● Virus lysogeny incorporation
Answer: Viral nucleic acid incorporates onto the host chromosome
This virus is called a prophage
