Chapter 13 video Notes Flashcards
Virus characteristics
- Not cells (acellular)
- Not considered alive
- Smaller than prokaryotic cells must use an electron microscope to see
- structure is protein capsid coating and nucleic acid
- replicate by hijacking host cell
- don’t exhibit metabolism
- Have DNA or RNA never both
- measured in nanometers (nm)
What types of host can viruses attack?
- All types of organisms are susceptible to virus attacks.
- Most will only be able to infect the cells of one or a few spaces of organism
Examples:
Bacteriophages - viruses that infect bacteria
or
Animal or plant viruses
What type of host does the virus attach to?
Viruses can be host-specific
- infect only a particular kind of cell in the host (ex HIV)
or
Viruses can be host generalist
- Infect many kinds of cells in different host
(ex rabies)
What structures are found in all viruses?
-Capsid
-Genetic material
- Glycoproteins
What is a capsid and its function?
- Capsid is made of proteins called capsomeres
-Provide shape
-Protects genetic information - Shape will be different based on the virus
What are the three shapes of capsid and their function?
- Helical - rod-shaped capsomeres that bond together to form a tube around the nucleic acid (ex tobacco mosaic virus)
- Polyhedral - Roughly spherical (ex common cold)
- Complex - may have multiple types of proteins and take a shape that is not asymmetrical and does not fit into either category (ex rabies)
Genetic Information in Viruses
- Found in all viruses
- Show more variety in their genomes than cells do.
- The primary way scientists classify viruses
- May have DNA or RNA but never both ( can be dsDNA, ssDNA, dsRNA, and ssRNA )
- May be linear and segmented or singular and circular
- Much smaller than genome cells
What are Viral Spikes?
- Composed of glycoproteins
- Protruding outward from the virus’s surface
Function - Allows the virus to attach and enter a host cell
- In animal viruses called spikes
- In bacteriophages called spikes
- Always mutating
- play a role in host recognition
What is the viral envelope?
- Composed of phospholipid bilayers and proteins
- Acquired from its host cell during viral replication or release
- not all have it.
What is the function of the viral envelope?
- Protect the virus from the host cell.
- But they are more fragile
- Susceptible to detergents, alcohol,, and drying out
What are Matrix protein enzymes?
-Not found in all viruses
- Enzymes for specific operations within their host cell
- polymerase that synthesis DNA and RNA
- replicas that copy RNA
- Reverse transcript synthesis DNA from RNA
- Completely lack the genes for the synthesis of metabolic enzymes
How do scientists classify viruses?
- Type of nucleic acid ( DNA or RNA, Genome SS or DS
- Presence or absence of an envelope.
- SHape of Capsid ( Helical, Icosahedral, or Complex
- Size
What are the two bacteriophage replication cycles?
Virulent bacteriophages
-Lytic viral replication cycle
Temperate bacteriophages
- Lysogenic viral replication cycle
What are the stages of the lytic cycle?
- Attachment - Phage’s tail fibers attach to complementary receptor proteins on the surface of the bacteria
- Entry - Phage releases an enzyme to break the cell wall, injecting the genetic material into the host cell.
- Synthesis - the bacterium begins to synthesize a new virus under the control of the viral genome.
- Assembly - Parts spontaneously assemble into bacteriophages
- Release - Becomes so packed with viruses that lyse (split open), releasing mature virions
Will the Lysogenic cycle kill the Host cell?
No, the Phage genome integrates into the bacterial chromosome
