Viral Structure and Functions

Summary

Viruses are unique pathogens with simple structures, lacking cellular components, yet capable of infecting all types of cells. They can exist extracellularly as virions, inactive and protected by a protein capsid, or intracellularly where they become active, inducing host cells to produce viral components. Viruses exhibit various shapes due to capsid symmetry: helical, icosahedral, or complex. Their genetic material, either DNA or RNA, determines their replication strategy, with RNA viruses being more prone to mutations due to less accurate replication processes.

Takeaways

• 🦠 Viruses are unique pathogens with a simple structure, lacking a cytoplasmic membrane, cytosol, or functional organelles.
• 🌐 They can infect all types of cells and even bacteria, which are known as bacteriophages.
• 🔄 Viruses cannot perform metabolic activities on their own and must invade other cells to replicate.
• 🧬 In the extracellular state, viruses are called virions and are non-reproductive, consisting of a protein coat (capsid) surrounding a nucleic acid core.
• 🌐 Enveloped viruses have an additional phospholipid membrane derived from the host cell, while non-enveloped viruses lack this membrane.
• 🔬 Viruses come in various shapes and sizes, including helical, icosahedral, and complex forms, which are determined by the capsid symmetry.
• 🌀 Helical viruses have a central cavity or hollow tube made by proteins arranged in a circular fashion.
• 🔶 Icosahedral viruses are composed of equilateral triangles fused together in a spherical shape, enclosing the genetic material.
• 🧬 Complex viruses combine icosahedral and helical shapes and may exhibit a head-tail morphology, which is unique to bacteriophages.
• 🧬 The viral genome contains the genetic material, which can be either DNA or RNA, and is usually small with only a few genes necessary for replication.

Q & A

What is unique about viruses as pathogens?

Viruses are unique pathogens due to their simple cellular organization and distinct pattern of multiplication. They lack a cytoplasmic membrane, cytosol, or functional organelles but can infect all types of cells.

How do viruses infect bacteria?

Viruses that infect bacteria are called bacteriophages. They are not capable of metabolic activity on their own, so they invade bacterial cells and use their metabolic machinery to produce more viral molecules.

What is the difference between extracellular and intracellular states of a virus?

In the extracellular state, the virus is called a virion and is not capable of reproducing. In the intracellular state, the capsid is removed, and the virus becomes active, inducing the host to synthesize viral components.

What are the components of a virus in its extracellular state?

In its extracellular state, a virus consists of a protein coat called a capsid surrounding a nucleic acid core, which contains the genetic material or the viral genome.

What is the function of the capsid in a virus?

The capsid is an outer protein coating that protects the viral genome and aids in its transfer between host cells.

What are the three types of shapes that viruses can have according to their capsid symmetry?

Viruses can have helical, icosahedral, or complex shapes according to their capsid symmetry.

How does the structure of a helical virus differ from that of an icosahedral virus?

Helical viruses have a capsid with a central cavity or hollow tube made by proteins arranged in a circular fashion, creating a tube with room for the nucleic acid in the middle. Icosahedral viruses are made up of equilateral triangles fused together in a spherical shape that fully encloses the genetic material.

What is the significance of the viral genome?

The viral genome contains the genetic material, which can be either DNA or RNA, and it holds the information necessary for the virus to replicate and produce viral proteins.

Why do RNA viruses tend to have more mutations than DNA viruses?

RNA polymerases are more likely to make copying errors than DNA polymerases, leading to more frequent mutations in RNA viruses during transcription.

How do enveloped viruses differ from non-enveloped viruses?

Enveloped viruses have a phospholipid membrane derived from the host cell called an envelope that surrounds the nucleocapsid, while non-enveloped or naked viruses lack this membrane.