Biological Membranes

Learning Objectives What Is the Nature of Biological Membranes? What Are Some Common Types of Membrane Proteins? What Is the Fluid-Mosaic Model of Membrane Structure? What Are the Functions of Membranes? Prostaglandins and Leukotrienes, and What Do They Have to Do with Lipids?

Biological Membranes In aqueous solution, phosphoglycerides spontaneously form into a lipid bilayer, with a back-to-back arrangement of lipid monolayers polar head groups are in contact with the aqueous environment nonpolar tails are buried within the bilayer, the major force driving the formation of lipid bilayers is hydrophobic interaction * The arrangement of hydrocarbon tails in the interior can be rigid (if rich in saturated fatty acids) or fluid (if rich in unsaturated fatty acids).

- Membrane consist of fatty acids ,phospholipid, cholesterol, ,sphingolipid, sphingomyelins . And those were the components of lipid . -Lipids connect together by hydrophobic interaction . -Phospholipid is like microphone : it has polar head “hydrophilic : loves water “ and hydrocarbon tail “hydrophobic : hates water \ away from water”. The polar head and hydrocarbon tails form two layers of membrane ” biological membrane”.

Biological Membranes A lipid bilayer Liposome a Micelle

-unsaturated >> cis configuration \ has an angle Saturated >> trans configuration -Biological membrane has 3 shapes : a-lipid bilayer Hydrophilic surfaces and hydrophobic tails b- Micelles The Way Lipid Absorbed From Intestinal lumen to intestinal cells then proteins are added to form chylomicrons that walks in lymphatic system and goes to thoracic duct in the general circulation and goes to Adipose tissue and muscles to support them with fatty acid that needed for energy then to the liver to be distributed .

-Micelles holds cholesterol, fatty acids ,fat soluble vitamins , vitamin D, Calcium , and bile.. - Chylomicrons are the largest lipid and consist of 90% of TG. After the chylomicrons are distributed from liver the liver makes new TG in the form of very low density glycoproteins . C-Liposomes وسيلة لدخول انواع من drugs and viruses في ال thereby .

Lipid Movement in Membranes

Lipid Movement : 1- Lateral No ATP Easy Fast 2-Flip Flop Requires too much of ATP Slow يتنقل بمسافات اكبر *** Cholesterol > Animal source And not available in the plants كل الزيوت النباتية لا تحتوي على cholesterol

Biological Membranes 1. The presence of cholesterol increases rigidity with heat, membranes become more disordered; the transition temperature is higher for more rigid membranes; it is lower for less rigid membranes 2. Plant membranes have a higher percentage of unsaturated fatty acids than animal membranes 3. The presence of cholesterol is characteristic of animal rather than plant membranes. 4. Animal membranes are less fluid (more rigid) than plant membranes. The membranes of prokaryotes, which contain no appreciable amounts of steroids, are the most fluid.

-Membranes are affected by temperature -Membranes are affected by temperature . -One Characteristic of biological membrane is that it has things inside and out of it Such as : Phospholipid + cholesterol ,glycoprotein (carbohydrate and protein ),glycolipid (lipid and carbohydrate),integral protein “consist of one or multiple polypeptide chains”. Proteins types: 1-integral proteins Permit the surface of membrane and maybe expose on both sides 2-peripheral proteins On the surface , could be outside or inside (asymmetrical ).

Membrane Dynamics Acyl Group in the Bilayer Interior Are Ordered to Varying Degrees Relatively low temp: semisolid gel phase Intermediate temp: liquid-ordered state Relatively high temp: liquid-disordered state

All Biological Membranes Share Some Fundamental Properties Fluid mosaic model for membrane structure

Inside-Outside Two main categories of membrane proteins: Peripheral proteins - bound to the surface of the membrane Outside / inside – different (asymetrical) Integral proteins - permeate the surface of the membrane, they may be exposed on both sides. © 2016 Paul Billiet ODWS

Different kinds of phospholipids- * Note their asymmetric distribution in the two membrane leaflets WITH CARBOHYDRATE

The phospholipid in the previous slide are components of the membrane . **The most important of all phospholipids : Phosphatidyl-ethanolamine and phosphatidyl-choline.(major compounds) ***The most important thing in the membrane \what distinguishes the fluid mosque model ? the differences in the sugar group (carbohydrate). Different types of sugars distinguishes different type of membranes. -The sugars are outsides on the surface of the membranes and they're markers for the membrane.

The Composition and Architechture of Membrane Each Type of Membrane Has Characteristic Lipids and Proteins

Asymmetric distribution of phospholipids between the inner and outer monolayers of the erythrocyte plasma membrane

The percentage of proteins differs from one organ to another . Multiple scleroses : when myline sheets are damaged *** membranes lipid also differs from outside to inside the erythrocyte. “ Mainly most of them are inside “ - Peripheral proteins can be removed easily .

Peripheral Membrane Proteins Are Easily Solubilized Peripheral and integral membrane proteins Inhibitor protein

Integral Proteins Are Held in the Membrane by Hydrophobic Interactions with Lipids Integral membrane proteins

Peripheral protein consist of one or multiple phospholipid (different amino acid) and the amino group can be inside or the carboxyl group could be inside . Protein may be either free or anchored .

Covalently Attached Lipids Anchor Some Membrane Proteins Lipid-linked membrane proteins

Membranes function as selective chemical barriers- Membrane permeability fat soluble ,penetrate easily Penetrate less and in less concentration Pass very slowly and needs carriers Don’t pass

Simple Diffusion

Glucose, sodium ions, and chloride ions are a few examples of facilitated diffusion Needs Carrier or gate .

The Chloride-Bicarbonate Exchanger Catalyzes Electrochemical Cotransport of Anions across the Plasma Membrane

Three general classes of transport systems

Always negative charges if one goes out the other have to go inside to save the balance . Uniport >> just one moves in one direction Cotransport >> two moves at the same time A- symport : two moves at the same time and same direction (sodium and glucose)>> opposite charges. B-antiport : moves in opposite directions (chloride and bicarbonate , Na+ and K+ ).>> two same charges .

Active Transport Results in Solute Movement against a Concentration or Electrochemical Gradient LOW CONCENTRATION HIGH CONCENTRATION

Three types of diffusion : 1-facilitated :fast and doesn’t require high energy ,needs carrier or gate 2-simple: needs carrier and more ATP 3- passive >> slow and needs energy 4-Active >> Needs Carrier and against conc ***In the primary active transport : X will move against the concentration gradient (NEEDS carrier and ATP). Secondary active transport : (NEEDS carrier and ATP) S enters and X Exits .

Passive Transport Is Facilitated by Membrane Proteins Energy changes accompanying passage of a hydrophilic solute through the lipid bilayer of a biological membrane

Facilitated diffusion is different from free diffusion in several ways First, the transport relies on molecular binding between the cargo and the membrane-embedded channel or carrier protein. Second, the rate of facilitated diffusion is saturable with respect to the concentration difference between the two phases; unlike free diffusion which is linear in the concentration difference. Third, the temperature dependence of facilitated transport is substantially different due to the presence of an activated binding event, as compared to free diffusion where the dependence on temperature is mild.

Affected by temperature Can be saturated NO saturation

Postulated mechanism of Na+ and K+ transport by the Na+K+ ATPase Potassium is important to muscles and heart To treat hypotension and some arrhythmias. It acts by inhibiting the Na/K-ATPase, also known as the sodium-potassium ion pump. H+ will move with K+ to save the balance 2K+ and H+ equals 3Na+

Energy Transduction by Membrane Proteins ANTIPORT SYMPORT

Glucose transport in intestinal epithelial cells

Regulation by insulin of glucose transport by GLUT4 into a myocyte Glucose transporter

Galactose is faster than glucose in absorption Glucose is higher conc than galactose ,it has kinetic advantage **It needs carrier to move from intestinal lumen to intestinal cells and the carrier holds Na+ Na+ ,Glucose cotransport(helper) \ symport *** وجود الinsulin يغني عن Na-K pump ويسمح لل glucose بالدخول . ***يزداد ال insulin عند زيادة السكر .

Lactose uptake in E. coli

A Defective Ion Channel in Cystic Fibrosis Topology of cystic fibrosis transmembrane conductance regulator (CFTR)

Mucus lining the surface of the lungs traps bactieria