Viruses: The Robot Hackers of Microbiology

Key Characteristics of Viruses

Viruses are extremely small.
Comparison of sizes:
- Typical virus: very small
- Bacteria: 100 times larger than a virus
- Eukaryotic cell: 1000 times larger than a virus
Variability in virus size can help distinguish between different viruses.

Capsid: Protein coat that gives viruses their shape.
- Made up of building blocks called "capsomers".
Common shapes:
- Icosahedral: 3D, six-sided diamond-like shape.
- Helical: Appears as a cylinder due to a helical wrapping of monomers.
- Spherical: Sometimes covered by an envelope which adds an additional layer.

Viruses have unique nucleic acids:
- Single-stranded DNA
- Single-stranded RNA
- Double-stranded DNA (common in human cells)
- Double-stranded RNA
Viruses can contain only one type of nucleic acid.
The combination of nucleic acid with the capsid is called a nucleocapsid.

Viruses are obligate intracellular parasites, needing a host to reproduce (hence the term "robot hackers").
Types of hosts:
- Bacteriophages: Viruses that infect bacteria.
- Eukaryotic viruses: Infect human and other eukaryotic cells.

Complex Virus Shape: Used by bacteriophages
- Nucleocapsid contains the nucleic acid.
- Sheath acts like a needle to inject nucleic acid into the host.
- Tail attaches to host bacteria.
Receptor-Mediated Endocytosis:
- Cells have receptors that viruses exploit to enter via endocytosis.
- Viruses trick receptors into forming pits, allowing entry.
Direct Fusion:
- Used mainly by enveloped viruses.
- Viruses fuse directly with the host membrane, allowing entry.

Viruses can be distinguished based on their size, shape, genetic material, and host type.
They are termed as "robot hackers" due to their ability to hijack host cellular machinery to replicate and survive.
Understanding the unique characteristics of viruses contributes to distinguishing them and comprehending their mechanisms of infection.