Module 5 Flashcards
What is a virus
-DNA or RNA (never both)
-Double stranded, single stranded
-Segmented (multiple fragments) or non-segmented (1 fragment)
Describe the structure of a virion
Some viruses carry enzymes:
-Bacteriophage have lysozyme-like enzyme
-RNA viruses have RNA replicase
-Retroviruses have reverse transcriptase
Compare helical vs icosahedral symmetry
Compare naked vs enveloped virion
How do we classify viruses
List the 7 baltimore classifications and their nucleid acid type/replication
How do lytic (virulent) bacteriophages infect bacteria
What is the one-step growth curve of infectious virions
Describe bacteriophage receptors
- outer membrane (Gram -)
LPS
-Common receptor for T4 phages
-Phages bind to O-antigen
Outer membrane Proteins (OMPs)
-Used by phages as recognition site
Porins
-Nutrient transport channels
- Cell wall receptors (Gram +)
Techoic acids (TAs)
-Polymers found in cell wall
Peptidoglycan
-Some phages recognize modifications in the peptidoglycan
- Appendage receptors (pili and flagella)
How do lysogenic (temperate) phages infect bacteria?
How do viruses infect eukaryotes
Describe the life cycle of human viruses
- Attachment: Virus “spike” proteins recognize and attach to receptors on host cell surface
-Very specific interaction
-Block interaction (drugs, vaccines, etc.) - Penetration: Attachment triggers viral entry
a. Receptor-mediated Endocytosis
* naked viruses
b. Receptor-mediated Fusion
* enveloped viruses - Uncoating
-Degradation of protein coat
-Same area for viral transcription - Biosynthesis
a. Viral nucleic acid is replicated, transcribed and translated
* New Viral proteins & nucleic acids
b. Dependent on host cell enzymes
* Exceptions: Viral DNA or RNA polymerases
c. Simple to very complex - Assembly
a. Production of new viruses
* “Assembly line”
b. Happens in Nucleus or cytoplasm
* Virus dependent - Release: Mature viruses exit the host cells
a. Naked viruses
* Lysis due to accumulation of viruses
* Host cell does not survive
b. Enveloped viruses
* Envelope acquired during release
* Viral spike proteins in host membrane
* “buds” out through host membrane
* Host cell may survive
* Continued slow release
What are the outcomes of a viral infection
how can we grow viruses
Describe the central dogma for viruses
-To create mRNA you need a negative strand DNA
-Tro create a protein, you need a positive strand RNA
Explain dsDNA viruses (BC1)
Genome: Double-stranded DNA
Replication Site: Usually the nucleus
Replication Process:
Virus enters the host cell and releases its dsDNA genome.
The dsDNA enters the nucleus and is transcribed into mRNA by host RNA polymerase.
The mRNA is translated into viral proteins in the cytoplasm.
The virus assembles new virions and exits the cell.
Explain ssDNA viruses (BC2)
Genome: Single-stranded DNA (ssDNA).
Replication Site: Nucleus
The virus enters the host cell and releases ssDNA.
Host DNA polymerase converts ssDNA into dsDNA.
The dsDNA is transcribed into mRNA by host RNA polymerase.
The mRNA is translated into viral proteins, leading to new virion formation.
Explain dsRNA viruses (BC3)
Genome: Double-stranded RNA (dsRNA).
Replication Site: Cytoplasm
Virus enters the host cell and releases dsRNA.
The viral RdRp transcribes the -RNA strand into +RNA (mRNA).
The mRNA is translated into proteins.
The virus assembles new virions and exits the cell.
Explain positive-sense RNA viruses (BC4)
Genome: Single-stranded RNA that functions directly as mRNA.
Replication Site: Cytoplasm
Virus enters the cytoplasm and releases its +ssRNA genome.
The +ssRNA is immediately translated into proteins, including RdRp.
RdRp synthesizes -ssRNA, which serves as a template for new +ssRNA.
The virus assembles and exits the cell.
Explain negative sense RNA viruses (BC5)
Genome: -ssRNA, which is complementary to mRNA.
Replication Site: Cytoplasm
Virus enters the cytoplasm and releases its -ssRNA genome.
Viral RdRp transcribes -ssRNA into +ssRNA (mRNA).
The mRNA is translated into viral proteins.
The virus assembles and exits the cell.
Explain reverse-transcribing (retroviruses) RNA viruses (BC6)
Genome: +ssRNA
Replication Site: Cytoplasm and nucleus
Virus enters the host cell and releases +ssRNA.
Reverse transcriptase converts RNA into dsDNA.
The dsDNA integrates into the host genome.
Host RNA polymerase transcribes viral mRNA.
The mRNA is translated into proteins.
compare retroviruses to proviruses
