Proteinsare building blocks of an organism, belong to a group of molecularcompounds in living organism, and are consisting of twenty differentamino acid chains. In living organism, each protein type has adifferent role that is defined by the sequence of a chain of theamino acid building blocks. Carrier proteins are the type of proteinsthat assist in the diffusion of molecular substances in and out of abiological membrane. The carrier proteins, therefore, are found inbiological membranes. Carrier membrane becomes an integral aspect ofthe membrane within which they facilitate transportation ofsubstances in and outside the cell of organisms. A membrane is a thinlayer that encloses cell organelles in the membrane. Looking at theproperties of a cell membrane, they are permeable, semi-permeable orselectively permeable. In that case, molecular substances may beselectively admitted in the cell for biochemical reaction necessaryfor the sustenance of life. Therefore, protein carriers come in andmediate the problem by facilitating movement of this selectivepermeability. Membranes contain fats and lipids that even resistabsorption of simple substances like water molecules.
Thereare two types of carrier protein categorized based on the mechanismused to transport molecules across the cell membrane. The first oneis called facilitated diffusion. In this type, movement of substancein or out of the cell does not require energy. Instead, movementoccurs through specific binding of molecules with protein carriers.Charged ions and large molecular substances are the dominantcandidates transported using this mechanism. The nature of thesetypes of carriers is that they do not freely translocate nor do theyrequire adenosine triphosphate (ATP) to function since they possessgated trans-membrane channels.
Activetransport carriers are the second in that category. As the namesuggest, it is the active uptake of substance in and out of the cellagainst its concentration gradient. The active uptake is necessarybecause it is used to provide molecular substance needed by the cellincluding glucose and amino acids. These types of protein carriersare also used when the cell membrane is completely permeable tomolecular substances. Adenosine triphosphate is used to providechemical a process referred to a primary active transport. However,when electrochemical gradient occurs when active uptake takes placewithout the use of energy from the cell a phenomenon referred to asecondary active transport. Active transport of substance aims atmoving molecules from a region of lower concentrations to those ofhigher concentration. Each carrier, therefore, has specific receptorsbonded to facilitate the function. Molecules to transport bind withthe carrier and is retained by the protein carrier. Later, thesubstance will translocate until it is facing the other side of theplasma membrane. The substance is released to the higher concentratedarea within its affinity (Schomburg& Schomburg, 2002).
Functionsof Carrier Proteins
Proteincarriers act as gates or doors to a plasma membrane and determinewhat gets in and out. The protein membrane channels the molecules tothe right entry of exit point in the cell membrane. Carriers help theactive uptake of substances inside or outside the cell, as the cellrequires. Active transport is the type of carrier protein thatfacilitates the function of active uptake. Help in facilitateddiffusion by binding specific carriers to particular molecularsubstances. They also help in bringing in ions inside the cell thatare important in biochemical reactions (Gropper,Smith & Groff, 2009).
(Dietmar),Schomburg, I., & Schomburg, D. (2002). Springerhandbook of enzymes..Berlin: Springer.
Gropper,S., Smith, J., & Groff, J. (2009). Advancednutrition and human metabolism.Australia: Wadsworth/Cengage Learning.