Problem 17 - Biology

Question

HIV (a) is a retrovirus (b) destroys T cytotoxic cells (c) is attacked mainly by B cells (d) a, b, and \(c\) (e) none of the preceding.

Step-by-Step Solution

Answer

The correct answer is (e), none of the preceding.

Step 1: Identify the Definition

First, let's identify the definition of a retrovirus. A retrovirus is a type of virus that replicates in a host cell through the process of reverse transcription using an enzyme called reverse transcriptase.

Step 2: Analyze Option (a)

HIV (Human Immunodeficiency Virus) is known to be a retrovirus because it uses RNA as its genetic material and converts it into DNA within a host cell. Therefore, statement (a) is correct.

Step 3: Analyze Option (b)

We know from the study of HIV/AIDS that HIV primarily targets and destroys CD4+ T helper cells, not cytotoxic T cells. So, statement (b) is incorrect.

Step 4: Analyze Option (c)

B cells are responsible for producing antibodies that can react with free virus particles or infected cells, but they are not primarily responsible for attacking HIV. The correct cells that attack the virus are primarily CD8+ cytotoxic T cells. Therefore, statement (c) is incorrect.

Step 5: Evaluate the Combined Option (d)

Since statement (a) is correct and both statements (b) and (c) are incorrect, option (d), which claims all statements a, b, and c are correct, is not valid.

Step 6: Determine the Correct Answer (e)

Given the analysis and evidence, the correct conclusion is that none of the preceding options fully describe HIV correctly as per the given choices. Hence, option (e) is correct.

Key Concepts

HIV

Human Immunodeficiency Virus, or HIV, is a virus that attacks the body's immune system, specifically the CD4+ T helper cells. The virus compromises the immune system, making it difficult for the body to fight off infections and diseases. If untreated, HIV can lead to the disease AIDS (Acquired Immunodeficiency Syndrome).

• HIV is a retrovirus, which means it uses a unique method to replicate inside the body.
• It mainly spreads through certain bodily fluids from an infected person, such as blood, semen, or breast milk.

Early detection and antiretroviral therapy (ART) are crucial in managing HIV, helping individuals live longer, healthier lives and reducing the risk of transmission.

T helper cells

T helper cells, or CD4+ cells, are a type of white blood cell that plays a central role in the immune system. These cells do not directly kill pathogens but act as the body's alarm bell. They recognize antigens (foreign substances) and activate other immune cells to combat invaders.
T helper cells stimulate:

• Activation of B cells to produce antibodies, which tag viruses and bacteria for destruction.
• Proliferation of cytotoxic T cells that directly destroy infected cells.

HIV targets these crucial cells, weakening the immune system and leaving the body vulnerable to opportunistic infections and illnesses.

reverse transcription

Reverse transcription is a unique process that retroviruses, like HIV, use to replicate within host cells. Unlike most organisms that transcribe DNA into RNA, retroviruses reverse this flow. They use an enzyme called reverse transcriptase to convert their RNA into DNA once inside a host cell. This newly formed viral DNA integrates into the host's genome, allowing the virus to hijack the host’s cellular machinery to produce new viral particles.
This ability to reverse the central dogma of molecular biology (DNA → RNA → Protein) is what classifies HIV as a retrovirus. Reverse transcription is a critical step in the HIV life cycle, and drugs that inhibit reverse transcriptase are key components of antiretroviral therapies used to treat HIV infections.

B cells

B cells are a fundamental component of the adaptive immune system. They play a vital role in humoral immunity, which involves the production of antibodies against pathogens. Each B cell is programmed to make a specific antibody that binds to a unique part of a foreign substance (antigen). Once a B cell encounters its specific antigen and receives a signal from T helper cells, it can differentiate into plasma cells to produce large volumes of antibodies.
Function of B cells in immune response:

• Neutralization of pathogens through antibody production.
• Tagging invaders for destruction by other immune cells.

Although B cells produce antibodies that can neutralize free virus particles, in the case of HIV, they are not the primary cells responsible for directly attacking the virus. Instead, cytotoxic T cells and continuous immune surveillance are crucial in combating HIV infections.