Question

Which of the following statements about virus structure is true? a. All viruses are encased in a viral membrane. b. The capsomere is made up of small protein subunits called capsids. c. DNA is the genetic material in all viruses. d. Glycoproteins help the virus attach to the host cell.

Short answer

Option D, "Glycoproteins help the virus attach to the host cell," is the correct statement about virus structure.

Step-by-step solution

Review all the options

Read all the given options carefully and understand what each option talks about the virus structure.

Option A

Option A states that "All viruses are encased in a viral membrane." This statement is not accurate because not all viruses have a viral membrane or envelope. While some viruses, like influenza and HIV, possess a lipid membrane, others, like adenoviruses and polioviruses, do not have one.

Option B

Option B states that "The capsomere is made up of small protein subunits called capsids." This statement is incorrect because capsomeres are the subunits that make up the protein shell, called the capsid. The terms should not be interchanged.

Option C

Option C mentions that "DNA is the genetic material in all viruses." However, this statement is false because some viruses contain RNA as their genetic material. For example, RNA is the genetic material of viruses like influenza and viruses that cause the common cold.

Option D

Option D states that "Glycoproteins help the virus attach to the host cell." This statement is true. Glycoproteins are present on the surface of viruses with a viral envelope, and they assist in the attachment and recognition of host cells. The glycoprotein spikes bind to specific receptors on the host cell's surface, which helps in infecting the cell.

Conclusion

Based on the analysis of all the options, option D, "Glycoproteins help the virus attach to the host cell," is the correct statement about virus structure.

Key concepts

Viral Membrane

Viruses can have various structures, and one of the key features is whether they have a viral membrane or not. A viral membrane is a lipid envelope that surrounds the capsid of some viruses. This membrane is derived from the host cell's membrane during viral replication and budding. Having an envelope makes it easier for the virus to fuse with other host cells, aiding in infection.

• Not all viruses have a viral membrane.
• Viruses with an envelope include influenza and HIV.
• Viruses without an envelope, known as non-enveloped viruses, include adenoviruses.

The presence or absence of a viral membrane has implications for how the virus is transmitted and how it can be targeted by antiviral drugs. Understanding this structure helps scientists develop treatments and prevention methods.

Genetic Material

The genetic material of a virus determines its classification and how it replicates. Viruses can have either DNA or RNA as their genetic material, which is unique compared to living organisms that typically have DNA.

• DNA viruses replicate using host DNA polymerases.
• RNA viruses must carry or synthesize their own RNA polymerase.

It's important to note that not all viruses contain DNA because RNA viruses, like the influenza virus, are quite common. This variety in genetic material also leads to different mutation rates, with RNA viruses generally mutating faster than DNA viruses due to lack of proofreading mechanisms.

Glycoproteins

Glycoproteins play a crucial role in the virus's ability to infect a host cell. These molecules are present on the surface of many viruses, especially those with an envelope. They consist of proteins that are conjugated with carbohydrates.

• Glycoproteins facilitate the virus's attachment to the host cell.
• They bind to specific receptors on the host cell's surface.

This interaction is like a lock and key, where the glycoproteins are keys that fit into host cell receptors, facilitating entry. This binding specificity can determine the range of host cells a virus can infect. Targeting glycoproteins is a strategy in developing vaccines and antiviral drugs.

Capsid

The capsid is the protein shell that encases the viral genetic material. It is made up of subunits called capsomeres, which assemble together to form the capsid's structure. This assembly provides both protection for the genetic material and a means to package it efficiently within the virus.

• Capsids can exhibit icosahedral, helical, or complex symmetry.
• They play a role in the virus's stability and infectivity.

The design of the capsid is crucial for the virus's ability to survive external conditions and deliver its genetic material into host cells. It also has antigenic properties, meaning it can trigger an immune response, which is useful in vaccine development.

Virus Host Interaction

The interaction between a virus and its host is central to understanding how infections develop. This interaction starts when a virus recognizes and binds to a host cell. The specificity of this binding affects the virus's host range and infection capabilities.

• Viruses use surface proteins, like glycoproteins, to attach to host cells.
• The host cell's receptors determine susceptibility to infection.

Once a virus attaches, it can enter the host cell and take over its machinery to replicate and produce new viral particles. This process can lead to cell damage or death, resulting in disease. Studying virus-host interactions helps in developing therapeutic strategies and understanding pathogen evolution.