Virus: Definition and Characteristics
A virus is a microscopic infectious agent that can only replicate inside the cells of a living host. It consists of genetic material (either DNA or RNA) enclosed in a protein coat. Viruses are not considered living organisms because they cannot carry out essential life processes without a host cell.
Viral Structure
Viruses have a simple structure consisting of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid. Some viruses also have an outer lipid envelope derived from the host cell's membrane.
Viral Replication
Viral replication involves the following steps:
- Attachment: The virus attaches to the host cell.
- Entry: The virus injects its genetic material into the host cell.
- Replication: The viral genetic material takes over the host cell's machinery to produce viral components.
- Assembly: New viruses are assembled from the replicated components.
- Release: The newly formed viruses are released from the host cell to infect other cells.
Types of Viruses
Viruses can infect various types of organisms, including animals, plants, and bacteria. They are classified based on their genetic material, structure, and mode of replication. Common types of viruses include DNA viruses, RNA viruses, enveloped viruses, and non-enveloped viruses.
Effects of Viruses
Viruses can cause a wide range of effects on their host cells, ranging from mild symptoms to severe diseases. Some viruses can lead to acute infections, while others may establish long-term, chronic infections. Additionally, certain viruses are associated with the development of cancers.
Study Guide
- Define a virus and explain why viruses are not considered living organisms.
- Describe the basic structure of a virus, including the role of the capsid and lipid envelope.
- Outline the steps involved in viral replication, including attachment, entry, replication, assembly, and release.
- Discuss the different types of viruses based on their genetic material and structure.
- Explain the effects of viruses on host cells, including acute and chronic infections, as well as their association with cancer.
