Acellular Pathogens Flashcards
What characteristics of life do viruses contain?
1) either an RNA or DNA genome that is surrounded by a protein coat (capsid)
2) phospholipid membrane that contains glycoproteins
What characteristics of life do viruses lack?
- cells, they are acellular pathogens that can infect all types of cells.
- lack genes that are required for reproduction and metabolism
What is a virion?
reproductive form of a virus that is made in the host cell
What is a virion made of?
- RNA or DNA genome
- protein coat (capsid)
- can be enveloped or non-enveloped (naked)
What does host range mean?
the type of host cell that a virus can infect
What determines host range?
whether a virus can attach to the surface of the host cell
What is a capsid?
protein coat that surrounds the nucleic acid of a virus
What are the capsid shapes found in viruses?
helical, polyhedral (icosahedral), or complex
What is a helical capsid?
rod-shaped hollow tube, its interior looks like a helix
What is a polyhedral (icosahedral) capsid?
it is three-dimensional and has many sides that are similar in shape. It has 20 sides and 12 vertices and looks similar to a soccer ball.
What is a complex capsid?
it is not polyhedral or helical. It contains structures at its base that make it complex.
What types of nucleic acids make up viral genomes?
1) made up of either DNA or RNA that can be single-stranded or double-stranded.
2) Their genomes can be segmented or nonsegmented.
3) RNA in the viral genome can be further classified into positive and negative strands.
How are viral genomes different from Bacteria, Archaea and Eukarya?
They are different from Bacteria, Archaea, and Eukarya since each of them only contain double stranded DNA.
What is a viral envelope?
phospholipid bilayer that contains glycoproteins, it surrounds the capsid of the virus
What is a viral envelope made of?
phospholipid bilayer and glycoproteins
Where does a viral envelope come from?
it is picked up by the virus and taken from the plasma membrane of the host cell when it buds off
What are the steps of the bacteriophage lytic cycle?
1) Attachment: A bacteriophage attaches to a specific bacterial surface receptor on the host cell.
2) Penetration: the bacteriophage injects the viral genome into the host cell.
3) Biosynthesis: It replicates, transcribes and translates the viral components it needs to build new viruses
4) Assembly: the maturation phase where new virions are assembled
5) Lysis: the cell lyses to release the mature viruses out of the host cell. These new viruses then infect new cells and the lytic cycle repeats
What are the steps of viral replication of animal viruses?
1) Attachment: Animal viruses bind to receptors on a host cell.
2) Penetration: receptor-mediated endocytosis of the virus, engulfing it in the cell. Enveloped viruses can also enter through membrane fusion between the membrane of the host cell and the viral envelope.
3) Uncoating: the envelope and protein coat of the virus get removed to expose the viral genome.
4) Biosynthesis: more parts are made to make new viruses
5) Assembly; Next, assembly occurs as new genomes are packaged into the capsid.
5) Release: the new viruses that are made bud off the cell and pick up the envelope. The viruses can also be released via lysis of the host cell.
What is lysogeny?
Lysogeny is the process that occurs when a temperate phage infects a bacterium.
1) It begins with the attachment of the bacteriophage to the host cell and penetration as it injects its viral genome.
2) Later, the bacteriophage DNA is integrated into the bacterial chromosome. After this step, the integrated genome is called prophage.
3) Then, the bacterial cells divide, and the prophage DNA is passed on to the daughter cells.
4) When the cell is under stressful conditions, the prophage DNA pops back out (excised)
5) lytic cycle begins with biosynthesis, then assembly, and finally lysis.
How is the replication cycle of HIV, a retrovirus, different than many other viruses?
HIV contains reverse transcriptase, a special enzyme in the capsid. Reverse transcriptase uses the positive single-stranded RNA genome as a template to produce a complementary single-stranded DNA copy. This single-stranded DNA is then made into double-stranded DNA that can become an integrated viral genome (provirus) that becomes a permanent part of the host cell. This allows the virus to stay in the host cell for a long time
What is latency?
the process in which a virus can stay hidden or is dormant inside the cell.
Why is latency important in certain cancers?
if a latent virus inserts itself in an important gene, it can trigger a path that leads to cancer
- ex: if it inserts itself in a tumor suppressor gene, the gene will not function anymore, and this could lead to cancer
What is a viral titer?
the amount of virion particles per unit volume
Why are viruses more difficult to study and identify in the lab?
1) they need a living host cell in order to replicate. They cannot be grown in pure culture by themselves.
2) It is also difficult to detect viruses.
