Question

Aquaporins are a. ion channels. b. water channels. c. receptors for ADH. d. small pores in the fenestrated capillaries of the glomerulus. e. part of a family of proteins encoded by genes found only in animals.

Short answer

Aquaporins are accurately described as water channels. The correct answer is (b) water channels.

Step-by-step solution

Understanding what Aquaporins are

Aquaporins are integral membrane proteins that serve as channels in the transfer of water, and in some cases, small solutes across the membrane. They are conserved in bacteria, plants, and animals.

Evaluating the options

Evaluation of options will involve assessing which statement accurately aligns with the definition of Aquaporins. Option a indicates that Aquaporins are ion channels, which is inaccurate as they mainly facilitate water movement. Option c suggests that Aquaporins are receptors for ADH, which is not entirely correct, as ADH influences Aquaporins but they are not receptors. Option d incorrectly describes Aquaporins as small pores in the fenestrated capillaries of the glomerulus. Lastly, option e incorrectly identifies Aquaporins as part of a family of proteins encoded by genes found only in animals, despite their conservation across bacteria, plants, and animals.

Selecting the correct answer

By correctly understanding the nature and function of Aquaporins, it is clear that the most accurate statement among the options is option b. Aquaporins are most accurately described as water channels, allowing water to move across cell membranes.

Key concepts

Membrane Proteins

Membrane proteins are essential components of biological membranes and play a pivotal role in various cellular processes. These proteins can be categorized based on their position and interaction with the membrane. There are two main types: peripheral and integral membrane proteins. Integral membrane proteins, like aquaporins, are embedded within the lipid bilayer and can span the entire membrane, creating channels through which molecules can pass.

These proteins are involved in a range of functions, including acting as gatekeepers that regulate the movement of ions and molecules into and out of the cell. Some are involved in cell signaling, whereby they receive chemical messages from other cells and trigger a response inside the cell. Membrane proteins are also important for maintaining cell structure and allowing cells to connect and communicate with each other.

Water Transport in Cells

Water transport across cell membranes is a fundamental process that is essential for maintaining cell turgor, volume, and homeostasis. Water can move through the cell membrane by passive diffusion, but this is a rather slow process. Cells often require a more efficient mechanism to regulate water transport to respond quickly to changes in their environment, which is where aquaporins come into play.

These specialized channels facilitate the rapid movement of water across the cell membrane in both directions, following osmotic gradients. This process is crucial for various physiological processes in organisms, including the regulation of water balance in kidneys, the rehydration of cells after osmotic stress, and the maintenance of water homeostasis throughout the body.

• Plant cells also rely on aquaporins for water uptake and release, affecting turgor pressure and plant growth.

Integral Membrane Proteins

Integral membrane proteins, such as aquaporins, are proteins that are permanently anchored or part of the membrane. They have one or more segments that are embedded in the hydrophobic region of the cell membrane. These proteins can either extend across the membrane, forming transmembrane proteins, or be attached to the inner or outer surface of the membrane.

Transmembrane proteins are often involved in transport functions because they can form channels or pores that allow substances to pass through, or they can function as transporters that change shape to move a substance across the membrane. Aquaporins, for instance, are a type of transmembrane protein specifically designed to transport water molecules. Understanding these proteins and their functions helps explain how substances selectively enter and exit cells, an essential aspect of cellular life.

• Aquaporins ensure the fast and efficient transport of water, which diffuses through their channel pores, maintaining vital cellular functions.