Module 18 Flashcards
Define a bacteriophage
a virus that infects a bacteria
Define a virus and give some general characteristics.
Acellular organisms that must infect a cellular host to survive and reproduce.
Their genome enters a cell, takes over, and directs the production of the viral components, protein, and nucleic acids to make virions.
-Obligate Intracellular Parasites
-Require other cells
-Only replicate in host cells
-Few or no enzymes of own metabolism-mainly use the hosts
What is the basic viral structure (what are the components) and what makes up each component?
Nucleic acid-either DNA or RNA
Protein capsid-protein coat that surrounds the nucleic acid.
May contain an envelope around the capsid-made up of lipids, proteins, and carbohydrates.
Describe the difference between the old and new taxonomic system for viruses.
The old system was based on the symptoms that were created or similar morphologies (Problems=may cause more than one disease state, can look the same but dramatically different in actions)
The new system starts with what nucleic acid is present, then the strategy for replication, and finally morphology
Classification is “new” and changing
What are the major steps for lytic bacteriophage infection also describe these?
Attachment-phage attaches to host cell wall
Penetration-penetrates cell via phage enzyme and injects DNA
Biosynthesis-phage DNA directs synthesis of viral components by host cell-eclipse period
Maturation-components assembled into virions
Release-cell lyses (phage lysozyme) and virions released
What is the difference between the lytic and lysogenic pathway in bacteriophage replication?
They both go through attachment and penetration but then the cell can continue with the lytic cycle or go to lysogeny
Lysogeny-Bacteria can reproduce normally (divide) with prophage genes repressed
phage conversion can happen
occasionally, viral DNA excises from bacterial DNA and then continues with lytic cycle
What is a prophage?
Bacteria where viral DNA integrates with bacterial DNA
What are some of the animal viruses life cycles?
Lytic
Persistent infections which are not completely cleared
-Latent-virus remain in host for long periods without producing disease (“repressed” state) and then reactivates
-Chronic-small amount of virus always found
What does a dsDNA virus do for biosynthesis/assembly?
Follow normal genetic flow of information
What does a ssDNA virus do for biosynthesis/assembly (different from dsDNA virus)?
Makes a single strand, double stranded by using an enzyme and then normal flow of genetic information
What does a +ssRNA virus do for biosynthesis/assembly?
Like mRNA, first finds ribosomes and makes proteins, makes capsids, make enzyme to make more
What does a -ssRNA virus do for biosynthesis/assembly (different from +ssRNA virus)?
Change RNA to mRNA then makes proteins
How does attachment, penetration, maturation and release steps differ between bacteriophage and animal viruses? Which type of virus does uncoating?
Bacteriophage-
–attachment-phage cell attaches to host cell wall
–penetration-penetrates via phage enzyme and injects DNA
–Maturation-components assembled into virions
–release-cell lyses and virions released
Animal-
–attachment-use receptor on plasma membrane of host cell but has no tails so there are attachment sites over the surface of the virus
–penetration-endocytosis (plasma membrane folds inward to form a vesicle which the virus is in-loses the envelop) and fusion (envelope fuses with plasma membrane and releases capsid
–Maturation and release-lysis if non-enveloped (blow up) or budding if enveloped (push against plasma membrane-surrounds and free)
Uncoating is done by the animal viruses
Is there any similarity on the release step (option) between bacteriophage and animal viruses? What is it?
For both, there is an option for the cell to lyse but the animal virus has to be non-enveloped
What are some antiviral drugs which interfere with DNA and RNA synthesis (be able to describe these)?
Acyclovir-Herpes virus, shingles treatment
–virus infected cells use the drug in place of normal nucleoside which leads to DNA synthesis issues
–can be administered orally, topically, or injected
Ribavirin-Hepatitis C and respiratory syncytial virus
–involves high mutation rate of RNA virus
Zidovudine (AZT)-HIV treatment
–competitive analog blocks synthesis by reverse transcriptase
–fairly toxic
