Question 1

Which of the following organelles is used as a sorting and recycling station in the receptor mediated endocytosis pathway?

Accepted Answer

Early endosomes serve as sorting stations in the receptor-mediated endocytosis pathway, where they direct internalized molecules to different destinations, such as recycling back to the plasma membrane or onward to lysosomes for degradation.

Question 2

The interaction between the viral particle and the host cell receptor is a major determinant of the species specificity of viral infections.

Accepted Answer

The interaction between viral particle and the host cell receptor is crucial for viral entry, replication, and spread, and it often determines the host range and species specificity of viral infections. Different viruses utilize different receptors, and the availability and compatibility of these receptors on the host cell surface could limit or enhance viral tissue tropism and pathogenicity. Thus, the viral-host receptor interaction is a critical factor in determining viral infection outcomes and transmission potential.

Question 3

What mechanism do most retroviruses, but not HIV, use to get their genome into the host cell nucleus?

Accepted Answer

Retroviruses typically wait until the host cell undergoes mitosis, during which the nuclear envelope breaks down, allowing the viral genome to enter the nucleus. This is in contrast to HIV, which can enter the nucleus without waiting for mitosis, using a different mechanism.

Question 4

Which of the following statements is a good explanation for the observation that many different rhinovirus strains can all use the same host cell receptor?

Accepted Answer

The fact that many different rhinovirus strains can use the same host cell receptor suggests that the receptor binding site is buried at the base of a narrow canyon on the viral capsid which is inaccessible to antibody proteins. This structural feature would make it difficult for antibodies to bind to the virus and prevent it from entering host cells, which could explain why so many different strains are able to use the same receptor.

Question 5

Inhibition of the M2 protein of influenza with the drug amantadine will block which step of virus entry?

Accepted Answer

The answer of Inhibition of the M2 protein of influenza...

Question 6

Because of the rigid plant cell wall, the entry of plant viruses is difficult.Which of the following is a description of how plant viruses move between individual cells within in a whole plant?

Accepted Answer

Plant viruses move between individual cells within a whole plant by using plasmodesmata, small channels that connect adjacent plant cells and allow the movement of molecules and particles between them. The size exclusion limit of plasmodesmata can be increased by viral movement proteins, which facilitates the transfer of viral particles from one cell to another.

Question 7

Most DNA viruses replicate in the cytoplasm of the host cell, since the ribosomes they need to translate their mRNAs are located in this cellular compartment.

Accepted Answer

Most DNA viruses replicate in the nucleus of the host cell because they need to access the host cell's DNA replication machinery for their replication. However, some smaller DNA viruses like parvoviruses do replicate in the host cell's cytoplasm.

Question 8

Which of the following is the best description of a syncytia?

Accepted Answer

A syncytia is a fusion of two or more cells caused by the action of viral envelope glycoproteins. This is a common mechanism used by some viruses, such as HIV and herpes simplex virus, to spread from cell to cell and evade the immune system. The resulting structure is a multinucleated cell with multiple nuclei but no intervening cell membranes.

Question 9

Which of the following is an accurate description of cavelolae?

Accepted Answer

Caveolae are small, flask-shaped invaginations of the plasma membrane that are enriched in cholesterol, sphingolipids, and caveolin proteins. They play a key role in regulating membrane trafficking, signaling, and lipid metabolism.

Question 10

Many large DNA viruses use which of the following cellular components to get their nucleocapsid near to the host cell nucleus

Accepted Answer

Many large DNA viruses, such as herpesviruses and adenoviruses, use microtubules to transport their nucleocapsid from the cytoplasm to the host cell nucleus. Microtubules are part of the cell's cytoskeleton and play a role in intracellular transport. Once the virus reaches the nucleus, it can use nuclear pore complexes to enter the nucleus and deliver its DNA to the host cell genome.

Question 11

Adenoviruses use which of the following entry mechanisms?

Accepted Answer

Adenoviruses use the interaction between the penton base of the virus and the cellular integrin proteins to cause the endosome membrane to lyse open and release the viral genome into the host cell cytoplasm. The fibers on the virion do not penetrate the endosome membrane, the capsid does not form a pore through the cell membrane, and the viral envelope does not fuse with the nuclear membrane.

Question 12

Orthymyxoviruses and paramyxoviruses both bind to which receptor on the surface of which host cells?

Accepted Answer

Both orthomyxoviruses and paramyxoviruses bind to receptors on the surface of host cells that have sialic acid, a type of carbohydrate. This is the key binding factor for both types of viruses.

Question 13

Unenveloped viruses must get their genome past the hydrophobic cell membrane.Some accomplish this by doing which of the following?

Accepted Answer

Unenveloped viruses can directly create a pore through the membrane and extrude the genome into the cytoplasm without the help of vesicles or coated pits. This process is referred to as "pore formation".

Question 14

Most viruses must exit the endosome before it fuses with a lysosome.Why?

Accepted Answer

To avoid being degraded by lysosomal proteases and nucleases.

Question 15

The major different between class I fusion proteins and class II fusion proteins is that ….

Accepted Answer

Class I fusion proteins undergo large conformational changes during the fusion process, which is a key characteristic distinguishing them from class II fusion proteins.

Question 16

A soluble form of the CD4 protein was once investigated as a treatment for HIV infection.How would this protein work to block infection.

Accepted Answer

The answer of A soluble form of the CD4 protein...

Question 17

Which of the following is an example of a virus that requires two different host cell receptors to complete its entry into the host cell?

Accepted Answer

Both HIV and Adenovirus require two cell receptors for entry. HIV requires both CD4 and a co-receptor, while Adenovirus requires both the primary receptor CAR and a secondary receptor integrin. The other viruses listed only require one receptor for entry.

Question 18

As part of an experiment, you take a solution of purified influenza virus particles and lower the pH of the solution to 5.5.You then add the virus to a culture of the appropriate host cell.What do you think would happen?

Accepted Answer

Lowering the pH to 5.5 can cause the hemagglutinin (HA) protein of the influenza virus to undergo a conformational change that inactivates its ability to mediate fusion between the viral envelope and the host cell membrane, thus preventing the virus from entering the host cell.

Question 19

Which of the following describes the function of dynein?

Accepted Answer

Dynein is a motor protein that moves along microtubules towards the nucleus. It is involved in many cellular processes such as intracellular transport, mitosis, and ciliary/flagellar movement.

Question 20

Before the viral genome can be transcribed or replicated in a new host cell it must….

Accepted Answer

Before the viral genome can be transcribed or replicated in a new host cell, it must be uncoated in the appropriate compartment of the correct cell type. This is because the viral genome is usually packaged inside a protein coat when it enters a new host cell. The uncoating process involves the removal of this protein coat and allows the viral genome to be exposed and accessible to the host cell machinery for transcription and replication.

Quiz 4: Virus Entry