Final answer:
A molecule of glucose is carried across the plasma membrane in active transport by specific carrier proteins known as glucose transport proteins, or GLUTs, which rely on energy from ATP to function. Insulin increases the number of GLUTs on cell surfaces, aiding in the uptake of glucose especially when blood glucose levels are elevated.
Step-by-step explanation:
Transport proteins play a crucial role in the active transport of glucose across the plasma membrane. Unlike passive transport mechanisms, active transport requires energy, typically in the form of ATP, to move substances against their concentration gradient. Carrier proteins, often described as pumps, are integral to this process.
In the context of glucose transport, specific carrier proteins called glucose transport proteins, or GLUTs, facilitate the movement of glucose and other hexose sugars into cells. While insulin doesn't act directly as a transport protein, it does increase the number of GLUTs on cell surfaces, promoting glucose uptake when blood glucose levels are high. This is a critical process, especially in the regulation of blood sugar levels and is notably impaired in individuals with diabetes.
Three types of carrier proteins are recognized: uniporters that transport one type of molecule, symporters that move two different molecules in the same direction, and antiporters that transport two different molecules in opposite directions. For glucose, these carrier proteins bind to the glucose molecule on one side of the membrane, undergo a conformational change, and release the molecule on the other side. Active transport carrier proteins are distinguished from those involved in facilitated diffusion by their requirement for ATP to function.