What is plasma membrane?
Plasma membrane once called cell membrane refers to a very thin membrane surrounding the cell surface, which is mainly composed of membrane lipids and membrane proteins. The basic function of plasma membrane is to maintain the relative stability of intracellular microenvironment and to participate in material exchange, energy and information transmission with the external environment. In addition, it plays an important role in cell survival, growth, division and differentiation. In addition to cell surface membranes, eukaryotes also have many organelles separated by membranes. The membrane structure of these organelles is similar to that of plasma membranes, but their functions are different. These membranes are called intimal membrane. The intima includes nuclear membrane, endoplasmic reticulum, Golgi body membrane and so on. Because the bacteria have no intima, the plasma membrane of the bacteria acts as a substitute for the plasma membrane.
What is membrane protein？
The protein contained in the biofilm is called membrane protein, which is the main undertaker of biofilm function. According to the difficulty of protein separation and its location in the membrane, membrane proteins can be divided into three categories: external membrane proteins or peripheral membrane proteins, internal membrane proteins or integrated membrane proteins and lipid-anchored proteins. Membrane proteins include glycoproteins, carrier proteins and enzymes. Sugars are usually attached to the membrane proteins, which are equivalent to sending signals into the cell through changes in the molecular structure of the sugar itself. The function of membrane protein is multifaceted. Membrane proteins play a very important role in many life activities of organisms, such as cell proliferation and differentiation, energy conversion, signal transduction and material transport. It is estimated that about 60% of the drug targets are membrane proteins. Membrane proteins can be used as "carriers" to transport substances in and out of cells. Some membrane proteins are specific receptors for hormones or other chemicals, such as thyroid cells that receive thyrotropin from the pituitary gland. There are also a variety of enzymes on the membrane surface, so that specific chemical reactions can be carried out on the membrane, such as endoplasmic reticulum can catalyze the synthesis of phospholipids and so on. The recognition function of cells is also determined by the proteins on the surface of the membrane. These proteins are often surface antigens. Surface antigens can bind to specific antibodies.
The function and significance of membrane proteins
Membrane proteins are rich in function and participate in many important reactions of cells, including transporting substances in and out of cells as a carrier, acting as a specific receptor for hormones, or carrying cell recognition function, and responsible for signal transduction and cell-cell interaction. The expression of membrane protein increased significantly in the process of synaptic transformation from nerve cell growth cone to nerve synapse. Membrane protein is involved in the regulation of human blood pressure. NKCC2, a cotransporter of kidney, is directly regulated by membrane protein VAMP3, which in turn regulates blood pressure. Membrane proteins play an important role in life activities. when ligand molecules bind to membrane protein receptors, they will stimulate a series of reactions, and finally convert chemical signals into electrical signals, transmit them to the nervous system, and finally make corresponding instructions. The proteins that play a role in the cellular signal pathway are mainly membrane proteins, and the typical example is G-protein-coupled receptor (G-protein-coupled receptors,GPCRs) with seven transmembrane structures. Each GPCR can be recognized and bound by specific ligands, including small molecules of catecholamines, lipids and neurotransmitters, and macromolecules of hormones. Membrane proteins account for about 30% of all sequenced genomes. About 50% of the targeted molecules of drugs belong to membrane proteins, and the importance of membrane proteins is self-evident. Because of its extremely important biological and medical significance, the research of membrane protein has become an important part of protein science, structural biology and medical pharmacy, as well as the research basis of biomimetic membrane and bionic sensing technology. it has important theoretical and application value in industry, environment, national defense and other research fields.