A virus is defined as a submicroscopic infectious agent that contains a genome of either DNA or RNA protected by a protein coat called a capsid. This simple structure lacks the complexity of cellular organisms, making it entirely dependent on host cells for metabolic activity and reproduction.
712
What are the individual protein subunits that assemble to form the viral capsid called?
Capsids are composed of repeating protein subunits known as capsomeres. These subunits self-assemble around the viral genome to provide structural integrity and protection against environmental degradation. The arrangement of these capsomeres determines the symmetry of the virus, which can be helical, icosahedral, or complex, depending on the specific viral family.
713
In which year was Wendell Meredith Stanley awarded the Nobel Prize in Chemistry for his work on viruses?
Wendell Meredith Stanley received the Nobel Prize in Chemistry in 1946. He shared this prestigious award with John Howard Northrop and James Batcheller Sumner. Stanley was recognized specifically for his pioneering work in the isolation and crystallization of the Tobacco Mosaic Virus, which provided critical evidence that viruses could be crystallized like chemical substances while retaining their infectious properties.
714
In a bacteriophage, what structure encloses the viral core within the tail?
The tail of a bacteriophage consists of a central hollow tube (the core) surrounded by a contractile protein structure known as the sheath. This sheath plays a vital role during infection by contracting to inject the viral genetic material into the host bacterium.
715
What is the approximate size of a typical parvovirus?
Parvoviruses are among the smallest known viruses, typically measuring approximately 18 to 26 nanometers in diameter. Their small size is due to their limited genome, which usually consists of a single-stranded DNA molecule, necessitating the use of host cell enzymes for replication.
716
In which bacterial structure are insect-resistant genes typically located?
Plasmids are small, circular, extrachromosomal DNA molecules found in bacteria. They often carry accessory genes, such as those for antibiotic resistance or insecticidal proteins (like the Cry toxins in Bacillus thuringiensis), which provide a selective advantage to the host bacterium in specific environments.
717
Which cell type is considered a major component of the human immune system?
T lymphocytes, or T cells, are a type of white blood cell that plays a central role in cell-mediated immunity. They are responsible for identifying and destroying infected cells and coordinating the overall immune response against pathogens, making them a cornerstone of the immune system.
718
What is the standard acronym for Acquired Immune Deficiency Syndrome?
Acquired Immune Deficiency Syndrome is commonly abbreviated as AIDS. It is a chronic, potentially life-threatening condition caused by the human immunodeficiency virus (HIV), which damages the human immune system and interferes with the body's ability to fight infection and disease.
719
Which unit of measurement is typically used to express the size of a virus?
Viruses are submicroscopic infectious agents, typically ranging in size from 20 to 300 nanometers. Because they are significantly smaller than most bacteria and eukaryotic cells, they cannot be observed with a standard light microscope. The nanometer (nm), which is one-billionth of a meter, is the standard unit for measuring these extremely small biological entities.
720
In which part of the animal body do enteric bacteria typically reside?
Enteric bacteria, belonging to the family Enterobacteriaceae, are primarily found in the intestinal tracts of humans and other animals. These microorganisms are part of the normal gut microbiota, though some species can become pathogenic if they migrate to other parts of the body or if the balance of the gut flora is significantly disrupted.
