Lesson 4 - Viruses

Question 1

What are Viruses – The Boundary of Life?

Answer 1

• These are parasites responsible for causing many diseases in living things (herpes and HIV in humans, for example).
• Viruses are found everywhere.
• Viruses consist of a core of nucleic acid, either DNA or RNA, and a protective coat of protein molecules and sometimes lipids.
• In isolation, viruses and bacteriophages show none of the expected signs of life.
• They do not respond to stimuli, they do not grow, they do not do any of the things we normally associate with life.
• Strictly speaking, they should not be considered “living” organisms at all.
• However, they show one of the most important signs of life: the ability to reproduce at a fantastic rate, but only in a host cell.
• Bacteriophages attack bacteria (prokaryotes)
• Viruses attack eukaryotic cells.
• Once inside the host, the bacteriophage or virus will either go into a Lytic Cycle - destroying the host cell during reproduction.
• Non-cellular particle made of protein-covered genetic material (DNA or RNA) that can invade living cells
• Do not metabolize energy – NOT living
• Parasites – MUST have a HOST
• Enter the host cell and take over by altering the host’s genetic makeup
• Bacteriophage – viruses which infect bacteria
• Each virus can only infect certain cell types.

or

• It will go into a Lysogenic Cycle – a parasitic type of partnership with the cell

Question 2

What is The Viral Genome?

Answer 2

A viral genome is the genetic material of a virus, which can be either DNA or RNA, and can be single-stranded or double-stranded. This genetic material contains the instructions for the virus to replicate and infect a host cell.

• The genome of a virus consists of either DNA or RNA, not contained in a nucleus
• Can be single-stranded or double-stranded
• Can be linear or circular
• Very small = codes only for a few proteins

Question 3

What is Viral Reproduction (Lyric Cycle and Lysogenic Cycle)?

Answer 3

• Lytic cycle: Immediate disease symptoms
• Attachment
• Insertion
• Host DNA disrupted
• Replication of viral parts and Assembly
• Lysis (release)

*Lysogenic Cycle:
- Reproduction of the viral genome without killing the host cell
- After DNA injection into the host cell, the viral DNA incorporates itself into the bacterial genome
- A prophage, or provirus
- This reproduces along with the bacterium
- Stress/Environmental factors can trigger a lytic cycle

Question 4

What are some Different Transmission of Viruses?

Answer 4

• Respiratory transmission 🡪 Influenza A virus
• Fecal-oral transmission 🡪 Enterovirus
• Blood-borne transmission 🡪 Hepatitis B virus
• Sexual Transmission 🡪 HIV
• Animal or insect vectors 🡪 Rabies virus

Question 5

Viruses and Human Tumours

Answer 5

The relationship between viruses and human tumors is a significant area of research in cancer biology. Certain viruses, known as oncogenic viruses or tumor viruses, have been linked to the development of human cancers. These viruses can contribute to cancer through various mechanisms such as integration into the host genome, alteration of cell cycle control, and suppression of tumor suppressor genes.

• Epstein-Barr Virus
• Burkitt’s Lymphoma (cancer of the lymphatic system)
• Human papillomavirus
• Benign warts
• Cervical Carcinoma
• Human T-cell Leukemia Virus
• Leukemia

Question 6

Treatment of Viral Infections

Answer 6

• Viral infection can only be treated with antiviral medications by preventing the following:
• Attachment/Entry
• Nucleic acid replication
• Virus protein processing
• Virus maturation
• Viral infections can be prevented with vaccinations
• Antibiotics do not work against viral infections

Question 7

3 Types of Vaccination

Answer 7

• Live (infectious) attenuated agents
• Weakened or modified microbes so that they are less virulent
• Inactivated (non-infectious) whole
  agents
• Modified viruses so that they cannot trigger disease
• Subunit preparations
• Only part of the agent is used to provoke an immune response (protein of the virus or sugar coating of the virus)

Question 8

How Vaccinations Work

Answer 8

• To prepare your immune system so that it is ready (make enough antibodies) to fight when the virus invades the body
• It helps your white blood cells to “remember” the virus
• Once the virus enters the body, your immune system recognizes it and gets rid of it before you get ill