IMIN 200 Midterm 2
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What are the 5 steps in receptor mediated endocytosis?
- 1. Ligand binds a cell surface receptor. This diffuses into an invagination coated with clathrin.
- 2. The clathrin pit pinches off forming a 'coated vesicle'.
- 3. The clathrin uncoats the vesicle.
- 4. The vesicle fuses with the early endosome. The early endosome is acidic.
- 5. The acidification releases the ligand from the receptor, and receptor is returned to cell surface.
What protein does Poliovirus use as a receptor?
What protein does Rhinovirus use as a receptor?
Why cant mice get infected with Poliovirus or Rhinovirus?
The presence of the receptor determines specificity of a virus. Mice do not have Pvr and mouse ICAM-1 is different enough from human ICAM-1 that the virus cannot use it as a receptor.
Why is it significant that the receptor binding site on viruses are recessed?
Makes it difficult for antibiotics to get in there.
Why don't we mutate our ICAM-1 to not allow binding to rhinovirus?
We cant change or mutate ICAM-1 because it is also a binding site for LFA-1 which is important for our immune system.
Once inside the endosome the virus is exposed to an acidic environment, which virus (rhinovirus or poliovirus) is resistant to acid?
Poliovirus is resistant to acid. Rhinovirus is not
What does a neutralizing antibody do to a virus?
Blocks the binding of the receptor (ICAM-1) to the canyon.
When a virus is entering a cell, what interaction causes major structural changes to the capsid?
Interaction with Pvr
When Pvr interacts with a virus, which protein extends into to the host cell membrane forming a pore and allowing viral RNA to enter?
If a capsid coated virus is internalized by a macrophage, will it uncoat?
No, must bind to a Pvr to uncoat. If internalized by a macrophage it must escape in the early part of endocytosis.
What is a fusogen?
A fusogen is a protein that a enveloped virus will make to get out of the endosome
What is the cellular receptor for influenza?
Why can influenza infect many different species?
Sialic acid is an integral membrane glycoprotein, because it is not a specific protein is why it can have so many hosts.
what is the bond that human influenza hemagglutinin prefers to bind as? what about avian influenza hemagglutinin?
- Human: alpha (2,6) glycosidic bond
- avian: alpha (2,3) glycosidic bond.
In the acidic endosome, what two things undergo conformational change?
Hemagglutinin (HA) and the fusogen
Why does HIV package reverse transcriptase in the capsid
Reverse transcriptase copies RNA to DNA, HIV has 2 strands of RNA in it's capsid, once inside it makes DNA copies of itself and inserts them right into the host DNA.
What is interference?
Only 1 retrovirus can infect a cell
What cell types are infected by HIV?
Any cell that has a CD4 and chemokine (CCR5) receptor (macrophages and dendritic cells).
What are the steps in HIV fusion with the plasma membrane?
- 1. GP120 on HIV binds to CD4 on the T cell. which causes a conformational change exposing the CCR5 receptor.
- 2.GP120 then binds to CCR Receptor on the T-cell.
- 3. The fusion peptide is exposed and implants in the cell membrane.
What are the 3 enzymes that HIV uses to make it's own strand of DNA?
Reverse transcriptase, DNase H, and DNA polymerase.
Why does a positive strand virus make negative strands?
as a template to make new positive strand copies.
What are the two virally encoded proteases that cleaves an RNA translated polypeptide.
2Apro and 3Cpro
How does 3Dpol polymerase tell which is viral and host RNA?
It tells by the structure of the RNA, sequence dependent.
How is an attenuated virus made?
The pathogenic virus is isolated from a patient and grown in human cultured cells, the cultured virus is used to infect monkey cells. The virus acquires many mutations that allow it to grow well in monkey cells. The virus no longer grows well in human cells and may be a candidate for a vaccine.
Is Parvo (5kb) or Pox virus (130- 300kb) more likely to encode their own enzymes?
Pox, the larger the virus, the more likely it is to encode it's own enzymes.
How does the virus make sure that an RNA genome gets in every virion?
Cleavage of VP0 to VP2 and VP4 requires the RNA, RNA cuts VP4 from the inside.
What is a defensin?
Neutrophils contain granules that contain antimicrobial peptides including defensins.
What effector protein is made by the liver in response to proinflammatory cytokines?
What are the 4 specifically?
- Acute phase reactants.
- Serum amyloid protein
- c-reactive protein
- mannan binding lectin
What sugar is on the surface of bacteria that we make antibodies against?
galactose alpha (1,3) - galactose (aGal)
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