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
What are the steps in the Lysogenic Cycle?
- Attachment
- Entry
- prophage in chromosome - integrating with chromosome
- replication of chromosome and virus; Cell division
- Induction
- Synthesis
- Assembly
- Release
What is Lysogenic conversion?
- When a bacterium acquires a new trait from its temperate phage and alters the phenotype of the bacterium
Three types
- Corynebacterium diphtheriae = diphtheria toxin
- Vibrio cholerae = cholera toxins
- Chostridum botulinum = botulinum toxin
