Human Virology Flashcards
What do bacteriophages do to break through the tough layer of peptidoglycan and insert it’s DNA?
Release lysozyme which degrades peptidoglycan and enables the insertion of Viral DNA.
Differentiate between the ways viruses enter the host.
Direct penetration
Membrane fusion
Endocytosis
Direct Penetration - Virus without envelope attaches to cell by it’s capsid and sinks into the cell, by which the viral genome enters the cell.
Membrane fusion - Enveloped virus enters the cell in similar fashion to direct penetration, except envelope diffuses into cellular membrane and capsid and genome enter cell unscathed.
Endocytosis - Viral receptor attaches to host cell and triggers the host to engulf the virus allowing viral entry WITH it’s envelope. (Most common)
Why are viruses not considered “living” organisms?
They are considered non-living because they don’t do any metabolism extracellularly.
Why are Viruses considered “Darwinian machines”?
They are incredibly adaptable to change and can thrive amongst such changes. “Survival of the Fittest”
Viral disease is a failure of adaptation. Why?
Because survival of the fittest suggests that the most natures strives for adaptability. Virulent viruses are a failure of adaptation that seeks to destroy its host.
Differentiate between the metabolic capabilities of viruses and Cells.
Viruses have Ø metabolic capabilities on it’s own and require other cellular organism ATP
Cells use/create ATP, vitamins, lipids, nucleic acids, etc.
Differentiate between the reproduction of Viruses and Cells.
Viruses reproduce by assembling pre-formed components (Like lego)
Cells divide.
Differentiate between the hereditary material of Viruses and Cells.
Viruses have either single or double-stranded DNA/RNA (ssDNA, dsRNA, etc.)
Cells ALWAYS have dsDNA expressed into t/r/m/RNA
What distinguishing factors make viruses distinct from one another?
Different modes of replication
Different structures/sizes
Different range of possible hosts/cells (HIV -> T cells)
What is the Viral Capsid?
Protein coat for the virus that protects in and helps in entry to cells.
Explain the process of Membrane Fusion and how enveloped Viruses enter cells.
The viral envelope (Outer shell) fuses with the cell membrane of the host. The capsid and underlying genetic material enters the cell where the capsid disintegrates and the genetic material of the virus free floats.
For viral genomes to be synthesized inside host cells, what must be made to be read by host ribosomes?
mRNA molecules that can be translated by ribosomes
This can act directly as mRNA and can produce a negative complementary strand.
+ssRNA
acts as an mRNA that is read by host ribosomes.
What creates the complementary strand of -ssRNA for +ssRNA? What purpose does the -ssRNA strand have?
Viral RNA Polymerase
Acts as a template for the construction of +ssRNA
How are +ssRNA and retroviruses different?
Retroviruses do not use their +ssRNA genome as mRNA inside the host. They use reverse transcriptase on their +RNA to create DNA that serves as a template for further +RNA molecules
What significant issues is faced by -ssRNA viruses? How do they overcome this issue?
Host ribosomes can only read +RNA molecules, and they do not contain any within their genome.
Overcomes this issue by carrying RNA-dependent RNA Transcriptase which transcribes +RNA molecules from its -RNA genome… and business carries on as usual.
How do dsRNA viruses replicate?
+RNA molecule acts as mRNA for the translation of proteins, and creates RNA Polymerase that transcribes the dsRNA. Each strand acts as a template (Similar to DNA replication)
RNA polymerase synthesizes mRNA for all of the following Except: A/ ssDNA B/ dsRNA C/ dsDNA D/ All the above
B/ dsRNA
dsRNA synthesizes mRNA by its positive strand of RNA
Which of the following synthesizes its mRNA by using RNA dependent RNA Transcriptase? A/ Retrovirus B/ -ssRNA C/ dsDNA D/ dsRNA
B/ -ssRNA
transcribes +RNA molecules from its -RNA genome… and business carries on as usual.
\+ssRNA synthesizes its mRNA molecule by: A/ RNA-dependent RNA transcriptase B/ Using RNA polymerase C/ Using its genome to act as mRNA D/ Reverse transcriptase
C/ The +ssRNA can act as its own mRNA template to create complementary strands.
Reverse Transcriptase is used by which of the following to transcribe mRNA? A/ Retrovirus B/ -ssRNA C/ dsRNA D/ ssDNA
A/ Retrovirus
DNA synthesized from RNA by reverse transcriptase, mRNA transcribed from DNA by RNA polymerase
Explain the Lysogenic growth cycle of Viruses.
Viral DNA enters the cell but does NOT destroy host DNA. Rather, one piece of viral DNA is fused to another peice of host DNA and become part of the host chromosome. This inactive viral DNA is called a prophage. Every time the cell replicates, so is the prophage in the new cells; Therefore all daughter cells are infected with the virus. This process continues until environmental factors that harm the cell are triggered, in which the viral DNA removes itself from host chromosome and destroys the remaining host DNA. Then the viral genome promotes the formation of capsid proteins and then inserts itself into the newly formed components of phages that will be released from the cell during lysis and infect other cells. Restarting the whole process over again.
What does induction mean in the lysogeny cycle?
When viral DNA removes itself from host chromosome and begins to breakdown host DNA.
