Powerpoint: February 22 Viruses
Keywords: Virus, head, tail, DNA, RNA, protein capsid/coat, lipid membrane (or membrane envelope), antigens, lytic cycle, lysogenic cycle,
Textbook Pages: 17-1
Learning Objectives
- Identify the structures of bacteriophages and retroviruses
- Describe the life cycle of (1) Lytic and (2) Lysogenic viruses
- Describe the body’s defence mechanisms against a viral/bacterial infection
What are Viruses?
Viruses are defined as “noncellular particles made up of genetic material and protein that can invade living cells”. They do not belong to any of the five kingdoms of organisms. It isn’t even clear whether viruses are living or non-living. While they do evolve in so much as only successful viruses can propagate their genetic information, they do not have cells, do not grow or reproduce, and do not use energy the way living things do. They also cannot live independently of cells, as they depend on cells to replicate.
Nevertheless, viruses are fascinating tiny machines of nature that have been used and studied for a variety of purposes, such as in genetic engineering, combatting cancer, and to destroy harmful bacteria in foods. Some viruses are also responsible for some of the most debilitating diseases known to man, including HIV (Human immunodeficiency virus) leading to AIDS, mono, shingles, herpes and chickenpox.
Identifying Viruses
Viruses come in many shapes, sizes and life cycles. There are two specific groups of viruses we will focus on here.
DNA Replication
DNA do not techninically reproduce the way living organisms do. However, they do invade host cells, causing them to create more copies of viruses. There are two ways that this happens.
Thankfully, the human body also has some ways of protecting ourselves against viruses, at different levels of specificity.
Primary Line of Defense:
These forms of defense are non-specific, as in, it is to protect against any form of pathogen, virus, bacterial, protist, etc. |
– Skin
– Oil and Sweat – Hairs and cilia in mouth and nose – Stomach (acids) – Saliva, sweat and tears (lysozyme) |
Secondary Line of Defense:
These forms of defense are also non-specific, but are generally activated only when pathogens have invaded. |
– Inflammatory response: white blood cells
– Fever |
Tertiary Line of Defense
The most specific form of defense. These forms of defense are activated specifically to target the pathogen. This is usually done through antibodies that are produced based on the antigens on the surface of the pathogen. The antibodies can then target the pathogens. |
–Interferons : produced by cells to interfere with virus replication
– Antibody production: white blood cells produce antibodies |