Virus

What is a virus? - Small, particles consisting of strands of genetic materials (DNA or RNA) surrounded by a protective protein coating/capsule (which is called capsid)

• They are packages of genetic instructions that can enter and take over control of the cell and the cell will eventually make copies of the virus

Viruses: Living or Nonliving?

Characteristics of viruses

• Causes disease by attacking living cells of a host

• Have a highly specialized relationship with their host - Will only Intect animal or plant or bacteria

• Most have a very limited host range, however, some viruses, like rabies, can infect a broad range of hosts

• Size: 1/10th of the volume of a small bacterial cell

Basic Viral Structure

A. Capsid

• protein coat

• may be complex, with tail and long, leg-like fibres

• Great variation from simple rod shapes to elaborate geometric- type forms

B. Nucleic Acid Core

• may be DNA or RNA

• may be a single molecule, linear or circular

• may be single or double stranded

• can have less than 5 to several hundred genes

C. Envelope

• used to attach to a cell's surface

• protein molecules may stick out of the spikes' surface

• whit

• Lop blood cells are able to recognize these proteins as part of the immune response

Bacteriophages

• Some types of viruses can infect bacterial cells they are known as bacteriophages

• Bacteriophages do not enter their host cells, but rather inject their DNA in the bacterium and their protein capsule remains outside the cell

• They are used in the food industry to prevent bacteria that can cause food poisoning

Viral Replication - Infection

Two common infectious cycles:

1. Lytic (lysis) Cycle - the rupturing of a cell; occurs when newly made viruses are released from a host (immediate effect of the disease)

2. Lysogenic Cycle

• Reproduction of the viral genome without killing the host cell, it stays in a state of dormancy

• After DNA is injected into the host cell, the viral DNA incorporates itself into the bacterial genome

• Stress / environmental factors can trigger a lytic cycle

Why are viruses important?

• Viruses can range from having mild symptoms, such as the common cold to ones that can lead to death, such as AIDS

• Some viruses can even be linked to certain cancers

• Viruses can be transmitted easily from one person to another in a short period of time

• If this causes a large-scale outbreak in a particular region it is known as an epidemic (e.g., 2009 Gujarat hepatitis outbreak)

• If the viruses spreads on a global scale it is known as a pandemic (e.g.,
  COVID 19)

Vaccinations

• Viruses are not destroyed by antibiotics (penicillin works by breaking down materials in the cell walls of bacteria)

• Viruses are hidden in the cells and can remain dormant for a number of years

• Vaccines are:

• Given to humans to trigger their immune system (make antibodies)

• A mixture of dead or weakened parts of viruses

• This prevents the real (strong) virus from causing harm to the organism

Viruses: Living or Nonliving?