What are the Characteristics of Virus?

Sourav PanOctober 28, 2024

Answered

The characteristics of viruses are fundamental to understanding their biology and their impact on living organisms. Viruses exhibit a range of unique features that distinguish them from cellular life forms. Below are the key characteristics that define viruses:

• Size:
  • Viruses are generally small, with the smallest measuring approximately 20 nanometers (nm) in diameter. Common viruses, such as the influenza virus and human immunodeficiency virus (HIV), are about 100 nm in size.
  • Average human cells, in contrast, measure between 10 to 30 micrometers (μm), making them 100 to 1,000 times larger than the viruses infecting them.
  • Some viruses, such as poxviruses like the variola virus (which causes smallpox), can be as large as 400 nm, while others, such as filoviruses (e.g., Ebola virus), are around 80 nm in diameter but can extend over 1,000 nm in length.
  • Notably, certain large viruses that infect amoebas, such as megaviruses and pandoraviruses, can reach sizes of up to 1,000 nm.
• Obligate Intracellular Parasites:
  • Viruses are obligate intracellular parasites, meaning they rely entirely on the host cell’s internal environment to replicate and produce new infectious virus particles, known as virions.
  • They bind to the surface of a host cell to gain entry, whereupon they disassemble, and their genetic material, composed of nucleic acid, directs the synthesis of new virions through a process known as de novo replication.
  • This replication process differs from cellular division, as viruses do not grow or divide; instead, they utilize the host cell’s energy and machinery to assemble new virions from scratch.
• Genetic Material:
  • The genetic material of viruses can consist of either DNA or RNA, but never both simultaneously. Unlike living cells, which predominantly contain double-stranded DNA (dsDNA), viruses can have diverse forms of genetic material.
  • These forms include single-stranded DNA (ssDNA), single-stranded RNA (ssRNA), and double-stranded RNA (dsRNA). Viruses possess only one type of nucleic acid in their genomes.
  • The size of viral genomes varies significantly, typically ranging from 7,000 to 20,000 base pairs (bp). Some viruses, particularly certain dsDNA viruses, can have much larger genomes; for example, herpesviruses have genomes ranging from 120 to 200 kilobase pairs (kb), while pandoraviruses can contain up to 2.5 million bases, rivaling the genomic sizes of some bacteria.
• Comparison with Cellular Genomes:
  • In comparison, eukaryotic cells have much larger genomes. For instance, the smallest known eukaryotic genome, that of a red alga, comprises about 8 million base pairs, while a human cell contains over 3 billion nucleotides. The largest sequenced genome belongs to the loblolly pine tree, which has over 22 billion base pairs.