Most Important Acellular Life MCQs with Answers | Biology

Bacteriophages are characterized by their distinct head and tail structure, with tail fibers used for attachment to bacterial cells, a feature not typically found in enveloped animal viruses like HIV.

The chapter states that the number of capsomeres making up the capsid is specific to a particular virus, giving examples like Herpes virus (162) and Adenovirus (252).

Rous sarcoma virus (causing cancer in chickens) and Papovirus (causing warts) are both examples of animal viruses.

The capsid provides structural protection to the viral genome, helping it survive unfavorable conditions outside the host, although pH and temperature can still denature proteins.

The chapter explains that non-enveloped viruses survive longer because their protein capsids are generally more stable and less sensitive to environmental degradation than the lipoprotein envelopes of enveloped viruses.

TMV is a classic example of a virus with helical (rod-shaped) symmetry.

The viral core of HIV contains integrase, along with reverse transcriptase and protease, enzymes crucial for its replication cycle.

Iwanowsky's experiment demonstrated that the infectious agent of tobacco mosaic disease could pass through filters designed to retain bacteria, indicating it was smaller than bacteria and "filterable."

Prions are infectious proteins without nucleic acids, and viroids are circular RNA molecules without a protein coat. Viruses, however, always contain a nucleic acid genome (either DNA or RNA) surrounded by a protein coat.

The Human Immunodeficiency Virus (HIV), the causative agent of AIDS, was identified in 1984.

HIV is described as a spherical retrovirus in the provided text.

The HIV envelope contains two key glycoproteins: gp120 (for attachment) and gp41 (for fusion).

Reverse transcriptase is a crucial enzyme carried by HIV that synthesizes DNA from its RNA genome.

HIV specifically targets and attacks CD4+ Helper T cells, as well as macrophages and certain brain cells, by binding to their CD4 receptors.

After the formation of double-stranded cDNA, the integrase enzyme facilitates its integration into the host cell's DNA, forming a provirus.

Once the viral DNA of HIV is integrated into the host cell's DNA, it is referred to as a provirus.

During the asymptomatic carrier stage, initial flu-like symptoms like fever, chills, aches, and swollen lymph glands may occur, which later disappear.

HIV specifically attacks and destroys Helper T-cells, which are critical components of the immune system, leading to immunodeficiency and vulnerability to opportunistic diseases.

When the immune system is severely compromised by HIV, the body becomes susceptible to various infections and cancers that would typically be fended off by a healthy immune system; these are called opportunistic diseases.

ART is a combination of medicines that effectively controls the HIV virus, allowing patients to live longer, healthier lives and reducing transmission, but it does not cure the infection.

HIV is transmitted through the exchange of specific body fluids, and sharing contaminated needles or syringes is a significant route of transmission.

The chapter describes matrix proteins as forming a shell or layer located beneath the envelope and outside the capsid of the HIV virion.

The AIDS Related Complex (ARC) stage is marked by persistent symptoms such as swollen lymph glands, night sweats, and persistent diarrhea, among others.

Upon entry and uncoating, the HIV virion releases its viral RNA genome along with essential enzymes like reverse transcriptase, integrase, and protease into the host cell's cytoplasm.

Sharing personal items like toothbrushes and razors that might come into contact with blood or bodily fluids is a risk factor for transmission and therefore should be avoided, making it not a control measure.

The HIV envelope, composed of a lipid bilayer, is 'borrowed' or derived from the host cell's membrane when new virions bud off from the infected cell.

Integrase is one of the key enzymes carried by HIV, responsible for integrating the viral DNA into the host chromosome.

Skin cancer is explicitly mentioned in the text as an opportunistic disease that can affect AIDS patients due to their compromised immune system.

HIV is named for its effect of decreasing the number of Helper T cells, which are crucial for the immune system, thereby causing immunodeficiency.

The budding process, while releasing new virions, ultimately leads to the host cell's non-functionality and death.

The text explicitly states that HIV is not transmitted by mosquitoes or other insects, nor by casual contact like hugging or sharing toilets.

Severe weight loss and weakness, along with opportunistic infections, are hallmarks of the final stage, Full Blown AIDS.

Viral protease is responsible for cleaving large viral polyproteins into individual functional proteins required for assembling new virions.

The chapter's description of HIV's life cycle mentions that after cDNA synthesis, the viral genomic RNA is disintegrated by ribonuclease.

ART is described as highly effective in controlling the virus, preventing disease progression, and allowing HIV-positive individuals to live longer, healthier lives, though it is not a cure and can have toxicities.

Glycoprotein gp120 on the HIV envelope is specifically responsible for binding to the CD4 proteins on the surface of target cells.

HIV enters by fusion of its envelope with the host cell membrane via gp120–CD4–coreceptor binding, releasing the capsid into the cytoplasm.

In the asymptomatic carrier stage, initial symptoms may subside, but the individual remains highly infectious, and HIV antibodies become detectable.