Introduction:
Living cells, whether prokaryotic or eukaryotic do have biological membranes that could serves as the barrier between cellular components and whole extracellular environment. Biological membranes have trilaminar appearance when viewed under microscope, with two dark bonds on each side of light band. Overall width of different mammalian membranes is 7-10 nm, few membranes have smaller widths particularly intracellular ones. Although, electron microscopy has given us with very static picture of membranes, membranes are very dynamic with the movement which allows cellular and subcellular structures in eukaryotic cells to adjust their shape and move.
Chemical composition of biological membranes:
Lipids and proteins are the two major components of all membranes but amount differs really between different membranes. Intracellular membranes are known to have some proportion of protein due to greater enzymatic activity of the membranes. Membranes also have high amount of different polysaccharide (sugars) in form of glycoprotein and glycolipid. Free carbohydrates don't exist in membranes.
Lipids of membrane:
Three major lipid components of membranes are phosphoglycerides, sphingolipids and cholesterol. Individual cellular membranes also have small quantities of other lipids like triacylglycerol and diol derivatives. Percentage of each of major lipids differs significantly in different membranes and is most probably associated to specific roles of individual membranes.
Membrane proteins:
Membrane proteins are categorized into two. Peripheral membrane proteins (or extrinsic) that simply isolated from membranes by treatment of membrane with salt solution of low or high ionic strength, or extremes of pH or name is used to imply the physical location on surface of membrane. Peripheral protein many with enzymatic activity are frequently soluble in water and free of lipids.
Integral (or intrinsic) proteins need rather drastic treatment like use of detergent or organic solvents to be extracted from membrane. They generally have tightly bound lipid, which if removed leads to denaturation of protein and loss of its biological function. Removal of integral proteins leads to disruption of membrane while peripheral proteins can be removed with little or no change in integrity of membrane.
Carbohydrate of membranes:
Carbohydrates present in membranes are completely in form of oligosaccharides covalently joined to proteins to form glycoproteins and to lesser amount of lipids to create glycolipids. Sugars found in glycoproteins and glycolipids include Mannose, Glucose, Fucose, Galactose, N-acethylglucosamine, N-acetylgalactosamine and Sialic acid.
Molecular structure of membranes:
Basic structural characteristic of all membranes is derived from physicochemical properties of major lipids components, phosphoglycerides and sphingolipids. These are ampiphatic compounds with the hydrophilic head and hydrophobic tail .
These ampiphatic compounds because of their low solubility in water react in the unique fashion in aqueous systems. Under correct state these lipids molecules will come together to create spheres termed micelles with hydrophobic tails interacting to exclude water and charged polar groups on outside. Specific concentration of lipid needes for micelle formation is known as critical micelle concentration.
Also, depending on state, ampiphatic lipids will interest to form the bimolecular leaf structure with two layers of lipid in which polar group are at interface between aqueous medium and lipid whereas the hydrophobic tails react to form the environment which excludes water. This bilayer conformation is basic lipid structure of all biological membranes. Lipids bilayers are very stable structures. The lipid bilayer can close in on itself, forming the spherical vesicle separating external space from the internal compartment. These vesicles are known as liposomes. Based on physicochemical properties of lipids, their biochemical and electron microcopy investigations, knowledge of structure of biological membrane evolved. Basic structure is bimolecular leaf arrangement of lipids in which phosphoglycerides, sphingolipids and cholesterol are oriented so that hydrophobic portions of molecules interact to minimize the interaction with water or other polar lipids. Polar heads of ampiphatic compounds are at interface with aqueous environment. This arrangement of lipids is same as that if synthetic phospholipids, liposomes. The major problem to resolve, though has been to describe interaction of integral and peripheral proteins with lipid bilayer.
The number of models for biological membrane structure has been suggested dating back to 1935 by H Davson and Danielle that was refined by J.D. Robertson later. In early 1970s, G.L. Nichoson and S.J. Singer suggested Mosaic model for membranes in which it was recommended that proteins are on surface and on lipid bilayer. Some proteins could span lipid bilayer with their polar groups in contact with aqueous environment on both sides and hydrophobic portions interacting with lipids in interior of membrane. This model has been extensively refined and is referred to as fluid mosaic model to point to movement of both lipids and proteins in membrane.
Properties of biological membranes:
Function of membranes:
Tutorsglobe: A way to secure high grade in your curriculum (Online Tutoring)
Expand your confidence, grow study skills and improve your grades.
Since 2009, Tutorsglobe has proactively helped millions of students to get better grades in school, college or university and score well in competitive tests with live, one-on-one online tutoring.
Using an advanced developed tutoring system providing little or no wait time, the students are connected on-demand with a tutor at www.tutorsglobe.com. Students work one-on-one, in real-time with a tutor, communicating and studying using a virtual whiteboard technology. Scientific and mathematical notation, symbols, geometric figures, graphing and freehand drawing can be rendered quickly and easily in the advanced whiteboard.
Free to know our price and packages for online biology tutoring. Chat with us or submit request at [email protected]
tutorsglobe.com vegetative propagation by stem assignment help-homework help by online natural methods of vegetative propagation tutors
Complexometric Titration of Zn (II) with EDTA tutorial all along with the key concepts of Preparation of Solutions, Ammonia/Ammonium Chloride Buffer Stock Solution, Calcium Standard Solution, Standardization of EDTA Solution and Analysis of the Zinc Unknown
Physical and chemical characteristics of water tutorial all along with the key concepts of Physical and Chemical Nature of Freshwater, Water distribution, Carbon dioxide and Oxygen
tutorsglobe.com clinical and lab diagnosis assignment help-homework help by online mycoplasma tutors
Companies are legally obliged to differentiate, on the statement of financial position, among that part of the equity of shareholders which may be withdrawn and that part that may not.
tutorsglobe.com electric kettle assignment help-homework help by online water heaters tutors
tutorsglobe.com theory of computation assignment help-homework help by online computer science tutors
Light absorption-fate of the excited state tutorial all along with the key concepts of The Franck-Condon Principle, catalogue of several important photo physical processes, Photo-excitation by Stimulated Absorption, Vibrational Relaxation, Fluorescence
Manufacture of some heavy Inorganic chemicals tutorial all along with the key concepts of Chemical Industry, Sources of Inorganic Raw Materials, Beginnings of Chemical Industry, Sulphuric Acid and Sulphates, Nitrogen Compounds, Phosphorus Compounds, Chlor-Alkali Compounds and Titanium Dioxide
tutorsglobe.com immunity assignment help-homework help by online immunology tutors
tutorsglobe.com management of hazardous wastes assignment help-homework help by online waste management tutors
thermistor digitals usually comprise “built in” sensors and probes. they have to be calibrated throughout the manufacturing process and thus are not interchangeable.
tutorsglobe.com taenia solium assignment help-homework help by online medical parasitology tutors
Directors’ share option schemes have been a popular method of rewarding the directors of large listed companies and several arguments have been put forward to support their use.
Equivalent Circuits of Transistors tutorial all along with the key concepts of Bipolar Junction Transistor, Transistor Models, Common Base Configuration, Common Emitter Configuration, Common Collector Configuration, NPN Transistor, PNP Transistor, Transistor As A Switch
1937227
Questions Asked
3689
Tutors
1486370
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!