File Name: structure of cell membrane and functions .zip
The cell membrane also known as the plasma membrane PM or cytoplasmic membrane, and historically referred to as the plasmalemma is a biological membrane that separates the interior of all cells from the outside environment the extracellular space which protects the cell from its environment. The membrane also contains membrane proteins , including integral proteins that go across the membrane serving as membrane transporters , and peripheral proteins that loosely attach to the outer peripheral side of the cell membrane, acting as enzymes shaping the cell.
Cell membranes are an essential component of the cell, providing separation between the intracellular and extracellular environment. They are composed of lipids, proteins and carbohydrates. In this article we shall consider the main functions of the cell membrane, the composition of membranes and clinical conditions in which a portion of the cell membrane is abnormal. The membrane bilayer contains many kinds of phospholipid molecules, with different sized head and tail molecules.
The paucimolecular unit membrane model of the structure of the plasma membrane is critically reviewed in relation to current knowledge of the chemical and enzymatic composition of isolated plasma membranes, the properties of phospholipids, the chemistry of fixation for electron microscopy, the conformation of membrane proteins, the nature of the lipid-protein bonds in membranes, and possible mechanisms of transmembrane transport and membrane biosynthesis. It is concluded that the classical models, although not disproven, are not well supported by, and are difficult to reconcile with, the data now available. On the other hand, although a model based on lipoprotein subunits is, from a biochemical perspective, an attractive alternative, it too is far from proven. Many of the questions may be resolved by studies of membrane function and membrane biosynthesis rather than by a direct attack on membrane structure. National Center for Biotechnology Information , U. Journal List J Gen Physiol v. J Gen Physiol.
Cell Membrane: Structure and Physical Properties
Cell membrane , also called plasma membrane , thin membrane that surrounds every living cell , delimiting the cell from the environment around it. Outside the cell, in the surrounding water-based environment, are ions , acids , and alkalis that are toxic to the cell, as well as nutrients that the cell must absorb in order to live and grow. The cell membrane, therefore, has two functions: first, to be a barrier keeping the constituents of the cell in and unwanted substances out and, second, to be a gate allowing transport into the cell of essential nutrients and movement from the cell of waste products. Cell membranes are composed primarily of fatty-acid-based lipids and proteins. Membrane lipids are principally of two types, phospholipids and sterols generally cholesterol. Both types share the defining characteristic of lipids—they dissolve readily in organic solvents—but in addition they both have a region that is attracted to and soluble in water. Membrane proteins are also of two general types.
Integrated Molecular and Cellular Biophysics pp Cite as. The cell membrane or plasma membrane is a thin closed sheet that fulfils a double role: a morphological — delimitates the cell from its external microenvironment and confines all of its subcellular organelles; b functional — regulates the exchange of substance between internal and external media, maintains actively the ionic asymmetry between its sides, and intermediates internalization or externalization of physical and chemical signals important for cell functions. The plasma membrane undergoes continual changes both in its molecular composition and its structure i. It plays an important role in the economy of the cell, exerting a selective control on the entire traffic of ions, water, and molecules. The membrane is involved also in intake endocytosis and secretion exocytosis of large particles.
A biological membrane , biomembrane or cell membrane is a selectively permeable membrane that separates cell from the external environment or creates intracellular compartments. Biological membranes, in the form of eukaryotic cell membranes , consist of a phospholipid bilayer with embedded, integral and peripheral proteins used in communication and transportation of chemicals and ions. The bulk of lipid in a cell membrane provides a fluid matrix for proteins to rotate and laterally diffuse for physiological functioning. Proteins are adapted to high membrane fluidity environment of lipid bilayer with the presence of an annular lipid shell , consisting of lipid molecules bound tightly to surface of integral membrane proteins. The cell membranes are different from the isolating tissues formed by layers of cells, such as mucous membranes , basement membranes , and serous membranes. The lipid bilayer consists of two layers- an outer leaflet and an inner leaflet.
Cells exclude some substances, take in others, and excrete still others, all in controlled quantities. The plasma membrane must be very flexible to allow certain cells, such as red and white blood cells, to change shape as they pass through narrow capillaries. These are the more obvious plasma membrane functions. Among the most sophisticated plasma membrane functions is the ability for complex, integral proteins, receptors to transmit signals. These proteins act both as extracellular input receivers and as intracellular processing activators.
Сидя в одиночестве и собираясь с мыслями, Беккер посмотрел на кольцо на своем пальце. Зрение его несколько прояснилось, и ему удалось разобрать буквы. Как он и подозревал, надпись была сделана не по-английски. Беккер долго вглядывался в текст и хмурил брови. И ради этого стоило убивать.
Не обращая внимания на пролом в стене, он подошел к электронной двери. Створки с шипением разъехались в стороны. Он вошел. Сьюзан стояла перед ним, промокшая, взъерошенная, в его пиджаке, накинутом на плечи.
Она наклонилась и что было сил потянула ее, стараясь высвободить застрявшую часть. Затуманенные глаза Беккера не отрываясь смотрели на торчащий из двери кусок ткани. Он рванулся, вытянув вперед руки, к этой заветной щели, из которой торчал красный хвост сумки, и упал вперед, но его вытянутая рука не достала до. Ему не хватило лишь нескольких сантиметров.