Module 5 Flashcards
Describe the general characteristics of viruses (5)
- Infectious, acellular pathogens
- Obligate intracellular parasites with host and cell-type specificity
- DNA or RNA genome (never both)
- Genome is surrounded by a protein capsid and, in some cases, a phospholipid membrane studded with viral glycoproteins
- Lack genes for many products needed for successful reproduction, requiring exploitation of host-cell genomes to reproduce
How can viruses be pathogenic
- Cause abnormal growth of cell
- Cause cell death
- Alter cell’s genome
- Cause little noticeable effect in the cell
Describe how viruses use genetic information
Give examples of how viral genomes are organized at the nucleic acid level
- Double-stranded or single stranded DNA
- Double-stranded or single stranded RNA
- Positive-strand or negative-strand RNA
Briefly explain or describe viral life cycles
- Genome of a virus enters a host cell and directs the production of viral components, proteins and nucleic acids, needed to form new virus particles called virions
- New virions are made in the host cell by assembly of viral components
- New virions transport the viral genome to another host cell to carry out another round of infection
Distinguish with examples: Bacteriophages
- Viruses that only infect bacteria
- Also called phages
Distinguish with examples: plant viruses
Distinguish with examples: animal viruses
Explain why viruses may be considered obligate intracellular parasites
In order to survive and reproduce, viruses must infect a cellular host making them obligate intracellular parasites
What is a vector?
An animals that transmits a pathogen from one host to another
Mechanical vs biological vectors
Mechanical vector: Mechanical transmission occurs when the arthropod carries a viral pathogen on the outside of its body and transmits it to a new host by physical contact.
Biological transmission occurs when the arthropod carries the viral pathogen inside its body and transmits it to the new host through biting.
In terms of genome what kind of virus is herpes?
- Double stranded enveloped virus
In terms of genome what kind of virus is HIV
+ssRNA enveloped DNA
Explain the lytic life cycle
- ATTATCHMENT: The phage attaches to the surface of the host
- PENETRATION: The viral DNA enters the host cell
- BIOSYNTHESIS: Phage DNA replicates and phage proteins are made
- MATURATION: New phage particles are assembled
- LYSIS: The cell lyses, releasing the newly made phages.
Explain the lysogenic viral life cycle
- The phage infects a cell
- The phage DNA becomes incorporated into the host genome
- The cell divides and prophage DNA is passed on to daughter cells
- Under stressful conditions the prophage DNA is excised from the bacterial chromosome and enters the lytic cycle
- The cell lyses, releasing the newly made phages
- New phage particles are assembled
- Phage DNA replicated and phage proteins are made
Explain the process of viral replication as done by animal viruses: DNA
If genome is ssDNA, host enzymes will be used to synthesize a second strand that is complementary to the genome strand, thus producing dsDNA. The dsDNA can now be replicated, transcribed, and translated similar to host DNA.