Viral Infection
Virus Introduction and Structure
Definition of a Virus
A virus is a non-living particle that relies on a host to reproduce.
Explanation of Viruses as Non-Living
Viruses do not display all characteristics of living things, such as growth, metabolism, and homeostasis.
Examples of Viral Diseases
Measles
Covid-19
Mumps
Chickenpox
Influenza
Herpes
Warts
Common cold
Suspected Origin of Viruses
Evidence suggests viruses may have originated from cell components, as their genetic material resembles cell genes.
Ranking Sizes
From smallest to largest: Virus < Prokaryotic Cell < Eukaryotic Cell.
Structure of Viruses
The outer layer, called the capsid, is composed of proteins.
Inside the capsid, viruses can contain either DNA or RNA, but never both at the same time.
Bacteriophage Definition
A bacteriophage is a type of virus that specifically infects bacteria.
Reproduction Requirement
To reproduce, a virus must attach to a host cell.
The Lytic Cycle
Overview of the Lytic Cycle
Viral DNA is injected into the host cell and takes over its DNA, directing it to produce viral components. When the new viruses are assembled, the host cell bursts (lyses) to release them.
Definition of Lyse
To lyse means the host cell bursts, releasing newly formed viruses.
Active Virus Examples in Short Cycle
Common cold and influenza typically show symptoms within 1-4 days after infection.
The Lysogenic Cycle
Overview of the Lysogenic Cycle
In this cycle, the injected viral DNA integrates into the host’s chromosomes. The viral DNA can remain dormant within the host cell's nucleus for extended periods. When the host cell reproduces, it replicates the viral DNA as well.
Latent (Passive) Virus Examples
Herpes and HIV can remain dormant for years before manifesting symptoms.
Cycle Description
The lysogenic infection cycle is generally longer, allowing for a period where the virus is not actively reproducing, potentially for many years, before becoming active.
