Cell Membrane Proteins
By Adhrith Vutukuri
Introduction
The cell membrane is an important part of the human cell, and its functions are key to keeping our cells healthy. Membrane proteins are vital to many of these functions. For example, membrane proteins control what enters and exits the cell, are involved in signal transduction, and are involved in enzymatic reactions.
Membrane Transporters
One major type of membrane proteins are known as membrane transporters which play an essential role in mediating the uptake of nutrients and the removal of unwanted substances. This function makes these proteins a common drug target since they are involved in many diseases such as cancer. Membrane transporter proteins allow for the movement of molecules through two major mechanisms: active transport and passive transport. Primary active transport uses energy in the form of ATP to actively move molecules and secondary active transport uses H+ or NA+ electrochemical gradients to move molecules. Passive transport on the other hand receives no additional energy and just facilitates the passive movement of molecules through diffusion.
Cell Surface Receptor Proteins
Another major function of membrane proteins, specifically cell surface receptor proteins, is membrane-initiated signal transduction. Intracellular signals are initiated by ligand binding to a cell surface receptor. This then stimulates intracellular target enzymes which are either directly linked to the surface receptor or are indirectly coupled to the receptor by G proteins. A chain of various reactions follows this, transmitting the signal to intracellular targets through a process called intracellular signal transduction.
Peripheral and Integral Proteins
To function properly, all these membrane proteins need to be connected to the membrane. Different kinds of proteins connect to the membrane in different ways. Some extend through the lipid bilayer and have portions of their mass on both sides of the membrane. These proteins are called transmembrane proteins. Other proteins are simply attached to one side of the membrane. All membrane proteins can be categorized into two major categories based on how they connect to the membrane. These are integral and peripheral proteins. Most integral membrane proteins are transmembrane and have strong connections to membranes. Peripheral proteins, on the other hand, are attached just to the outer or inner surface of the membrane and thus are more easily dissociated from the membrane.
Conclusion
Overall, membrane proteins are a diverse group of proteins vital to the normal function of human cells. Many different types of membrane proteins work together to allow the complex function of our cell membranes.
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