HIV/AIDS Practice Questions
20 free HIV/AIDS practice questions for the Microbiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which specific receptor on the surface of T-helper cells does the HIV gp120 glycoprotein initially bind to?
- A CD4
- B CD8
- C CXCR4
- D CCR5
Correct answer: CD4
The gp120 envelope glycoprotein of HIV has a high affinity for the CD4 receptor found on T-helper lymphocytes, macrophages, and dendritic cells. This binding is the first essential step for viral attachment and entry into the host cell.
HIV is classified as a retrovirus because it possesses which unique enzyme?
- A RNA-dependent RNA polymerase
- B DNA-directed RNA polymerase
- C Integrase
- D Reverse transcriptase
Correct answer: Reverse transcriptase
Reverse transcriptase allows HIV to transcribe its single-stranded RNA genome into double-stranded DNA. This process reverses the normal flow of genetic information, which is the defining characteristic of the Retroviridae family.
Which viral enzyme is responsible for inserting the HIV DNA into the host cell's genome?
- A Protease
- B Reverse transcriptase
- C Helicase
- D Integrase
Correct answer: Integrase
Integrase catalyzes the site-specific cleavage of host DNA and the subsequent ligation of the viral DNA into the host chromosome. Once integrated, the viral DNA is referred to as a provirus and can remain latent for years.
The structural gene 'gag' in the HIV genome encodes for which of the following?
- A Capsid and matrix proteins (p24, p17)
- B Envelope glycoproteins (gp120, gp41)
- C Reverse transcriptase and Integrase
- D Regulatory proteins (Tat, Rev, and Nef)
Correct answer: Capsid and matrix proteins (p24, p17)
The 'gag' (group-specific antigen) gene encodes the precursor polyprotein that is cleaved into the structural proteins of the virus, including the matrix (p17), capsid (p24), and nucleocapsid (p7). The p24 protein is often used as a marker in early diagnostic tests.
Which coreceptor is typically utilized by 'macrophage-tropic' (M-tropic) strains of HIV during early infection?
- A CCR5
- B CXCR4
- C CD28
- D HLA-DR
Correct answer: CCR5
Early in the course of infection, HIV strains typically use the CCR5 coreceptor found on macrophages and memory T-cells. Individuals with a homozygous CCR5-delta32 mutation are notably resistant to infection by these strains.
The clinical diagnosis of AIDS is confirmed when the CD4+ T-cell count drops below which threshold?
- A 1000 cells/mm³
- B 500 cells/mm³
- C 50 cells/mm³
- D 200 cells/mm³
Correct answer: 200 cells/mm³
According to the CDC, an HIV-infected individual is diagnosed with AIDS when their CD4+ T-cell count falls below 200 cells/mm³ or if they develop an AIDS-defining opportunistic infection. This stage represents severe immune system failure.
Which HIV enzyme is targeted by a class of antiretroviral drugs used in HAART to block polyprotein cleavage?
- A HIV Protease
- B RNA Polymerase II
- C Integrase
- D Topoisomerase
Correct answer: HIV Protease
HIV protease is responsible for cleaving long polyprotein chains into smaller, functional individual proteins during the budding and maturation phase. Inhibiting this enzyme results in the production of immature, non-infectious viral particles.
What is the primary function of the HIV envelope protein gp41?
- A Binding to the CD4 receptor
- B Binding to the CCR5 coreceptor
- C Protecting the RNA genome from degradation
- D Mediating viral-host membrane fusion
Correct answer: Mediating viral-host membrane fusion
While gp120 handles the initial attachment to receptors, gp41 is the transmembrane subunit that undergoes a conformational change to facilitate membrane fusion. This allows the viral capsid to enter the host's cytoplasm.
Which opportunistic infection, caused by a fungus, was one of the first indicators of the AIDS epidemic?
- A Candidiasis (mucocutaneous infection)
- B Pneumocystis jirovecii pneumonia (PCP)
- C Aspergillosis (invasive pulmonary form)
- D Cryptococcosis (meningeal infection)
Correct answer: Pneumocystis jirovecii pneumonia (PCP)
Pneumocystis jirovecii pneumonia (formerly PCP) is a major AIDS-defining illness. It rarely occurs in immunocompetent individuals but causes life-threatening respiratory failure in those with severely depleted CD4+ counts.
The window period in HIV testing refers to the time between:
- A Infection and the onset of AIDS symptoms
- B Infection and the appearance of detectable antibodies
- C Starting HAART and achieving an undetectable viral load
- D Exposure and the integration of the provirus
Correct answer: Infection and the appearance of detectable antibodies
The window period is the duration after infection during which a person may test negative for HIV antibodies even though they are infected and highly contagious. Modern 4th generation tests shorten this period by detecting the p24 antigen alongside antibodies.
Which HIV gene product is responsible for downregulating MHC-I expression on the host cell to evade CD8+ T-cell detection?
- A Nef
- B Tat
- C Rev
- D Vpu
Correct answer: Nef
Nef (Negative Regulatory Factor) is a virulence factor that enhances viral replication and helps the virus escape the immune system. It does this by decreasing the surface expression of CD4 and MHC class I molecules on infected cells.
How does HIV-2 differ from HIV-1?
- A HIV-2 is more virulent and spreads more rapidly across populations
- B HIV-2 is primarily found in West Africa and is less pathogenic
- C HIV-2 lacks a lipid envelope and cannot bind to host cells
- D HIV-2 does not use reverse transcriptase for replication
Correct answer: HIV-2 is primarily found in West Africa and is less pathogenic
HIV-2 is less transmissible and progresses more slowly to AIDS compared to HIV-1. It is largely confined to West African populations, whereas HIV-1 is responsible for the global pandemic.
Which of the following is an example of a Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI)?
- A Zidovudine
- B Efavirenz
- C Ritonavir
- D Raltegravir
Correct answer: Efavirenz
Efavirenz is an NNRTI that binds directly to the reverse transcriptase enzyme at a site different from the active site, causing a conformational change that stops DNA synthesis. Zidovudine is a Nucleoside analog (NRTI).
Which malignancy, characterized by purple skin lesions and caused by HHV-8, is commonly associated with AIDS?
- A Burkitt Lymphoma
- B Hodgkin's Disease
- C Kaposi's Sarcoma
- D Basal Cell Carcinoma
Correct answer: Kaposi's Sarcoma
Kaposi's Sarcoma is a vascular tumor caused by Human Herpesvirus 8 (HHV-8). It was one of the first diseases used to define the clinical spectrum of AIDS and typically appears as red, purple, or brown skin nodules.
During the 'Clinical Latency' stage of HIV infection, which of the following is true?
- A The virus likely enters a dormant phase as replication slows dramatically
- B The virus is replicating at low levels and the patient may be asymptomatic
- C CD4 counts rise significantly as the immune system returns to full strength
- D The patient is no longer infectious and cannot transmit the virus
Correct answer: The virus is replicating at low levels and the patient may be asymptomatic
Clinical latency (or chronic HIV infection) involves active viral replication in the lymphoid tissues, even if the patient feels well. Without treatment, this stage can last 10 years or more, during which the virus gradually depletes the immune system.
What is the primary mechanism by which HIV causes a decline in CD4+ T-cells?
- A Direct viral lysis and apoptosis induced by viral proteins
- B Inhibition of T-cell maturation and release from the bone marrow
- C Differentiation of CD4+ cells into non-functional regulatory cells
- D Blockage of T-cell circulation in the blood
Correct answer: Direct viral lysis and apoptosis induced by viral proteins
CD4+ T-cells are lost through multiple mechanisms: direct killing by the virus (pyroptosis), apoptosis of uninfected 'bystander' cells due to chronic inflammation, and destruction of infected cells by CD8+ cytotoxic T-lymphocytes.
Which HIV regulatory protein facilitates the export of unspliced viral mRNA from the nucleus to the cytoplasm?
- A Tat
- B Rev
- C Vif
- D Vpr
Correct answer: Rev
Rev (Regulator of Expression of Virion Proteins) binds to a specific sequence on viral RNA called the RRE. This allows late-stage, unspliced or partially spliced mRNAs to bypass host nuclear export restrictions, enabling the synthesis of structural proteins.
In the laboratory, which test is traditionally used as a confirmatory test after a positive ELISA screening for HIV?
- A Western Blot
- B Gram Stain
- C Northern Blot
- D Dark-field microscopy
Correct answer: Western Blot
The Western Blot identifies specific viral proteins (like p24, gp120, and gp41) in a patient's serum. It is highly specific and was long used to confirm the results of a more sensitive but less specific ELISA screening.
Which of the following is NOT a major route of HIV transmission?
- A Unprotected sexual contact with an infected individual
- B Sharing needles during intravenous drug use
- C Mother-to-child transmission via breast milk
- D Respiratory droplets from coughing or sneezing
Correct answer: Respiratory droplets from coughing or sneezing
HIV is a blood-borne and sexually transmitted virus. It is not transmitted through casual contact, air, water, or insects because the virus is fragile and cannot survive long outside the human body or in non-body-fluid environments.
The use of Pre-Exposure Prophylaxis (PrEP) involves taking which type of medication daily to prevent infection?
- A Broad-spectrum antibiotics
- B Interferon-alpha
- C High-dose Vitamin C
- D Antiretroviral drugs
Correct answer: Antiretroviral drugs
PrEP consists of antiretroviral medications (usually a combination like Tenofovir and Emtricitabine) taken by HIV-negative individuals at high risk. It is highly effective at preventing the virus from establishing a permanent infection if exposure occurs.