All Free Biology MCQs with Answers

2961. In the case of HIV, only _ can infect host cells.

• A. Double-stranded DNA
• B. Single-stranded RNA
• C. Double stranded RNA
• D. Single stranded DNA

Explanation: While the original genetic material of HIV is single-stranded RNA, the virus undergoes a process called reverse transcription. During this process, the single-stranded RNA is converted into a complementary single-stranded DNA (cDNA) molecule. This cDNA is then integrated into the host cell's genome, forming a double-stranded DNA structure that can infect host cells.

2962. Some retroviruses can convert:

• A. Cancer cells into normal cells
• B. Cancer cells into germ line cells
• C. Cancer cells into degenerated cells
• D. Normal cells into cancer cells

Explanation: Retroviruses can cause cancer by inserting their genetic material into the host cell's DNA. This insertion can disrupt the normal function of genes that control cell growth and division, potentially activating oncogenes (genes that promote cancer) or inactivating tumor suppressor genes (genes that prevent cancer). Additionally, some retroviruses carry oncogenes themselves, directly introducing cancer-causing genes into the host cell. Over time, these disruptions can lead to uncontrolled cell growth and the development of tumors.

2963. The agent causing AIDS was identified by research teams from:

• A. Pasteur Institute in the USA
• B. National Institute of Health in France
• C. Pasteur Institute in the USA and the National Institute of Health in France
• D. Pasteur Institute in France and the National Institute of Health in the USA

Explanation: The Pasteur Institute is located in France, and the National Institute of Health (NIH) is located in the USA. The correct option accurately represents the collaboration between these two institutions in identifying the AIDS-causing agent, which is the human immunodeficiency virus (HIV).

2964. The following are the means of transmission of AIDS, EXCEPT:

• A. Intimate sexual contact and breastfeeding
• B. Use of common syringes and surgical instruments
• C. Blood transfusion without screening
• D. Human immunodeficiency virus

Explanation: HIV, the virus causing AIDS, spreads through specific means: intimate sexual contact, breastfeeding, shared needles or unsterilized surgical tools, and unscreened blood transfusions. The virus itself isn't a method of transmission; rather, it's the agent transmitted via these routes.

2965. Now a vaccine against _ has been synthesized, and its experimental administration in humans started in South Africa.

• A. Hepatitis C
• B. Hepatitis A
• C. HIV
• D. Hepatitis B

Explanation: It was claimed in 2001 that a vaccine against HIV had been developed, and after successful trials, it would be on the market for consumers.

2966. HIV is uncoated:

• A. Outside the cytoplasm
• B. At the surface of the host cell
• C. Inside the cytoplasm
• D. Inside the nucleus of the host cell

Explanation: After entering the host cell, HIV undergoes a process called uncoating, during which the viral capsid that surrounds its genetic material is disassembled. This step occurs after the virus fuses with the host cell membrane and releases its core into the cytoplasm. The uncoating process allows the viral RNA and essential enzymes, such as reverse transcriptase, integrase, and protease, to be released into the host cell's cytoplasm. Once uncoated, the viral RNA becomes accessible for reverse transcription, where it is converted into complementary DNA. This newly formed viral DNA is later transported into the nucleus, where it integrates into the host cell's genome, initiating the next stages of the HIV replication cycle.

2967. In the infection cycle of HIV, RNA is converted into a DNA duplex by:

• A. Replication
• B. Transcription
• C. Reverse transcription
• D. Translation

Explanation: The answer is "Reverse Transcription."Explanation: RNA is converted into DNA by a process called reverse transcription. It is controlled by the reverse transcriptase enzyme.

2968. In the infection cycle of HIV, after attachment, there comes:

• A. Entry
• B. Uncoiling
• C. Reverse transcription
• D. Integration

Explanation: The answer is "Entry." Explanation: In the infection cycle of HIV, V occurs after the attachment of the virus to the host cell, followed by entry, which is followed by uncoiling.

2969. The CD4 receptor-bearing T lymphocyte is infected by:

• A. HIV
• B. HBV
• C. HCV
• D. HAV

Explanation: The answer is "HIV."Explanation: Viruses are intracellular obligate parasites, and they require a specific receptor site for their adsorption. The receptor site required by HIV is called the CD44 receptor site (cluster of differentiation 4). It is a cluster of specific glycoproteins that develops on the surface of T4 lymphocytes.

2970. The following are true about the head of the T4 phage EXCEPT:

• A. Hexagonal structure
• B. Pyramidal structure
• C. Prism-shaped structure
• D. An oval structure

Explanation: The answer is "An oval structure."Explanation: The head of a bacteriophage is an elongated, pyramidal, hexagonal prism-shaped structure to which a straight tail is attached. The head of the T44 phage is not oval. It is a prolate icosahedron, which means that it is shaped like a sphere that has been stretched out along one axis. The head of the phage is about 50 nanometers in diameter and 100 nanometers long.