Virus Structures and Life Cycles

Virus Characteristics

• Viruses are nonliving particles that require a host to reproduce.
• Main reasons for being categorized as nonliving:
  • Lack organelles for nutrient uptake and energy use.
  • Cannot produce proteins.
  • On their own, they cannot move or replicate.
• While many viruses are not harmful, they can infect and damage various living organisms.

Basic Structure of Viruses

• All viruses share a common structure comprising:
  • Inner genetic material (DNA or RNA).
  • Outer protein coat known as a capsid.

Size Comparison of Biological Structures

• Ordering from smallest to largest:
  • Prion
  • Viroid
  • Virus
  • Prokaryotic cell
  • Eukaryotic cell

Viral Replication Process

• Entry into Host Cell:
  • A virus must successfully attach to a host cell to replicate.
  • The virus's genetic material then enters the cytoplasm of the host.
  • Sometimes, the entire virus enters the host cell and the capsid disintegrates, exposing the genetic material.
• Two main cycles of viral replication:
  • Lytic Cycle
  • The virus uses the host's machinery to replicate immediately, leading to cell lysis (bursting) and release of new viruses.
  • Lysogenic Cycle
  • The virus integrates its DNA into the host's DNA, which can remain dormant until lytic cycle is triggered.
• Symptoms Onset:
  • Lytic Cycle: Symptoms appear soon after infection.
  • Lysogenic Cycle: Symptoms can take longer to manifest.

Types of Viral Infections

• Active Infection Viruses:
  • Cause immediate symptoms after replication.
  • Example: Identify and describe symptoms of one virus (search for detailed info).
• Latent Infection Viruses:
  • May remain dormant for a period before initiating the lytic cycle.
  • Example: Upon reactivation, one virus can show symptoms (search for detailed info).

Retroviruses

• Definition: Retroviruses are a type of virus that transcribes its RNA into DNA after entering host cells.
• Example: HIV (Human Immunodeficiency Virus)
  • Disease caused by HIV: AIDS (Acquired Immunodeficiency Syndrome).
  • Targeted cells: Primarily T-cells, which play a crucial role in the immune system.

Structure of HIV and its Functionality

• Key components:
  • Capsid: Protects viral RNA and assists in entering host cells.
  • RNA: Contains the virus's genetic information.
  • Glycoprotein: Helps in attaching and entering host cells.
  • Viral Envelope: Protects the virus and aids in attachment to host cells.
  • Reverse Transcriptase: Enzyme that converts viral RNA into DNA for integration into host DNA.

Understanding Vaccines

• Vaccine Composition:
  • The virus in vaccines is generally weaker than the actual pathogen.
• Immune Response:
  • Upon exposure to a foreign invader, the body produces antibodies.
  • Antibodies recognize specific aspects of the virus such as surface antigens.
• Antibody Recognition: True or False: Antibodies and antigens are shape-specific to one another. (True)

Challenges with Strep Throat Vaccine

• Vaccine Absence: Why is there no vaccine for the bacterial infection causing strep throat?
• Treatment: Utilize appropriate antibiotics to treat the infection.