Regulating membrane passage

Cell membrane, which encloses the cell and regulates the passage of ions, nutrients, metabolic products, and toxicant metabolites into and out of the cell interior when its membrane is damaged by toxic substances, a cell may not function properly and the organisms may be harmed ... 

Neuronal membranes contain phospholipids. A lack of essential fatty acids, such as omega-3 fats, or excessive intake of saturated fats, margarine, cholesterol, and animal fatty acids, can result in abnormalities. The neuronal cell membrane regulates the passage of molecules into and out of the cell. Neuronal membrane fluidity is believed to impact behavior, mood, and mental function. Physical properties, including the fluidity, of neuronal membranes affect neurotransmitter synthesis, signal transmission, uptake of serotonin and other neurotransmitters, neurotransmitter binding, and the activity of key enzymes that break down neurotransmitters like serotonin, epinephrine, dopamine, and norepinephrine. 

Where two cells in a tissue are touching, the membranes contain an organelle called a connexon which regulates the passage of ions and small molecules between the cells. The connexon is a cylinder composed of six identical protein subunits, which can move so as to create or eliminate a central pore (Unwin and Zampighi, 1980). 

Cell membrane, which encloses the cell and regulates die passage of ions, nutrients, lipid-soluble ( fat-soluble ) substances, metabolic products, toxicants, and toxicant metabolites into and out of the cell interior because of its varying permeability for different substances. The cell membrane protects Ae contents of the cell from undesirable outside influences. Cell membranes are composed in part of phospholipids that are arranged with dieir hydrophilic ( water-seeking ) heads on the cell membrane surfaces and dieir hydrophobic ( water-repelling ) tails inside die membrane. Cell membranes contain bodies of proteins that are involved in the transport of... 

PAHs are characterized by their high lipophilic affinity, which allows their fast absorption by the biological membranes and, consequently, their accumulation in the tissues (Tuvikene, 1995). Biological membranes are characterized as barriers between the cell and the environment, regulating the passage of toxic agents into the cellular interior and exterior (Stanley, 1992, 1994). Independently from the introduction via used, the chemical compoimd... 

Non-enzyme proteins as receptors. From about 1950, it began to be realized that the acetycholine receptor of muscle was a permease, namely a non-enzyme protein situated in the plasma membrane at the synapse. When coupled with ACh, it regulates the passage of sodium, potassiiun, and calcium ions (Karlin, 1974). Apparently, permeases provide the graded response needed at synapses. Initially, knowledge of permeases came from bacteria, where they were easier to isolate and study (see Section 3.1). Each molecule of ACh, by combining with its permease, allows 50 000 cations to cross the membrane (Katz and Miledi, 1972). 

Typically, functional porins are homotrimers, which assemble from monomers and then integrate into the outer membrane. The general porins, water-filled diffusion pores, allow the passage of hydrophilic molecules up to a size of approximately 600 Daltons. They do not show particular substrate specificity, but display some selectivity for either anions or cations, and some discrimination with respect to the size of the solutes. The first published crystal structure of a bacterial porin was that of R. capsulatus [48]. Together with the atomic structures of two proteins from E. coli, the phosphate limitation-induced anion-selective PhoE porin and the osmotically regulated cation-selective OmpF porin, a common scheme was found [49]. Each monomer consists of 16 (3-strands spanning the outer membrane and forming a barrel-like structure. 

Polypeptide hormones are usually stored in secretory granules after their passage through the endoplasmic reticulum and Golgi apparatus. Release of these hormones into the bloodstream is accomplished by fusing the secretory granule membranes with the plasma membrane. This event is often regulated by other hormones. 

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