Lipids and Proteins Are Associated in Biological Membranes Chapter 8

What is a lipid? insoluble in water Lipids: consists of nonpolar groups Classified on the basis of common solubility properties insoluble in water soluble in organic solvents like chloroform and acetone Amphipathic in nature Carboxyl group is hydrophilic and hydrocarbon tail is hydrophobic

What are the two groups of lipids? Lipids include: Open Chain forms fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, and glycolipids, lipid-soluble vitamins prostaglandins, leukotrienes, and thromboxanes Cyclic forms cholesterol, steroid hormones, and bile acids Open chain forms have polar head groups and long nonpolar tails

What are Fatty Acids? - Carboxyl group at polar end and hydrocarbon chain at non polar tail - Length of fatty acid plays a role in its chemical character - Usually contain even numbers of carbons (can contain odd, depending on how they are biosynthesized)

What are saturated fatty acids? Contain only C-C bonds - saturated

What are unsaturated fatty acids? In most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rare FA that contain C=C, are unsaturated Unsaturated fatty acids have lower melting points than their saturated counterparts the greater the degree of unsaturation, the lower the melting point. Plant oils are liquid at room temperature because they have more amounts of unsaturated fatty acids than do animal fats. Animal fats are solid. Fatty acids are rarely found free in nature, but they form parts of amny natually occurring lipids

What are triacylglycerols? Triacylglycerol (triglyceride): an ester of glycerol with three fatty acids natural soaps are prepared by boiling triglycerides (animal fats or vegetable oils) with NaOH, in a reaction called saponification (Latin, sapo, soap) When an organism uses fatty acids the ester linkages of triacylglycerols are hydrolyzed by enzymes called lipases. The other product of saponification is glycerol used in creams and lotions as well as manufacture of nitroglycerin. NaOH or KOH is used

What are soaps? Soaps form water-insoluble salts when used in water containing Ca(II), Mg(II), and Fe(III) ions (hard water) Results in characterisitc scum left on insides of bathtubs and sinks

What are phosphoacylglycerols? When one alcohol group of glycerol is esterified by a phosphoric acid rather than by a carboxylic acid, phosphatidic acid produced Phosphoacylglycerols (phosphoglycerides) are the second most abundant group of naturally occurring lipids Found in plants and animals

Other important members Phosphatidyl ethanolamine (cephalin), phosphatidyl serine, phosphatidyl choline (lecithin), phosphatidyl inositol, phosphatidyl glycerol and diphosphatidyl glycerol (cardiolipin)

What are Waxes? A complex mixture of esters of long-chain carboxylic acids and long-chain alcohols Found as protective coatings for plants and animals In plants they coat stems, leaves and fruit. In animals they are found on fur, feathers and skin. Myricyl cerotate found in carnauba wax used to polish floors. Cetyl palmitate is present in was produced by whales – used in cosmetics

What are Sphingolipids? Contain sphingosine, a long-chain amino alcohol sphingosine Found in plants and animals Abundant in nervous system Bares structural similarity to phospholipids

What are Glycolipids? a compound in which a carbohydrate is bound to an -OH of the lipid many glycolipids are derived from ceramides Gangliosides are Glycolipids with complex carbohydrate moiety that contains more than 3 sugars

What are Steroids? Steroids: a group of lipids that have fused-ring structure of 3 six-membered rings and 1 five-membered ring

Sex Hormones Androgens: male sex hormones synthesized in the testes responsible for the development of male secondary sex characteristics Testosterone Estrogens: female sex hormones synthesized in the ovaries responsible for the development of female secondary sex characteristics and control of the menstrual cycle A kind of steroid is sex hormone

What is Cholesterol? Present in biological membrane Does not occur in prokaryotes Precursor of vitamin D3 Harmful - when present in excess - Atherosclerosis Atherosclerosis – lipid deposits block blood vessels and lead to heart disease

What is the structure of lipid bilayers? The polar surface of the bilayer contains charged groups The hydrophobic tails lie in the interior of the bilayer Phosphoglycerides are lipid components of membranes

How does the composition of bilayer affect its properties? Both inner and outer layers of bilayer contain mixtures of lipids Compositions on inside and outside of lipid bilayer can be different This is what distinguishes the layers. The concentration of bulky molecules is higher in outer layer which has more room.

How does the composition of bilayer affect its properties? In saturated fatty acids, a linear arrangement of hydrocarbon chains leads to close packing of molecules in bilayer Provides rigidity

How does the composition of bilayer affect its properties How does the composition of bilayer affect its properties? (Unsaturated) Kink in hydrocarbon chain Causes disorder in packing against other chains This disorder causes greater fluidity in membranes with cis-double bonds vs...... saturated FA chains This is the effect of Double Bonds on the Conformations of Fatty Acids

Biological Membranes Plant membranes have a higher percentage of unsaturated fatty acids than animal membranes The presence of cholesterol is characteristic of animal rather than plant membranes Animal membranes are less fluid (more rigid) than plant membranes The membranes of prokaryotes are fluid - contain no steroids Oils derived from plant products are more liquid at room temperature than animal oil.

Temperature Transition in Lipid Bilayer • With heat, the transition temperature is higher for more rigid membranes - it is lower for less rigid membranes With heat, membranes become more disordered

Membrane Proteins Functions: transport substances across membranes; act as receptor sites, and sites of enzyme catalysis Peripheral proteins bound by electrostatic interactions can be removed by raising the ionic strength Peripheral proteins present on surface of membrane

Membrane Proteins Integral proteins bound tightly to the interior of the membrane can be removed by treatment with detergents or ultrasonification removal generally denatures them Integral proteins present within lipid bilayer

Fluid Mosaic Model Fluid: there is lateral motion of components in the membrane Proteins float in the membrane and can move along its plane of membrane Mosaic: components in the membrane exist side-by-side as separate entities Forms a lipid bilayer with proteins, glycolipids, and steroids such as cholesterol embedded in it no lipid-protein complexes, are formed

Fluid Mosaic Model of Membrane Structure

How does transport through membranes take place? Passive transport driven by a concentration gradient (from higher to lower) Simple diffusion: a molecule or ion moves through an opening Facilitated diffusion: a molecule or ion is carried across a membrane by a carrier/channel protein Transport through membranes takes place whether cells require energy or not. Passive transport moves in same direction of concentration gradient and cell does not expend energy. Simple diffusion- molecule passes through opening without interacting with another molecule. Small uncharged molecules such as O2, N2 and Co2 pass through membranes. Large molecules cannot pass through a membrane via simple diffusion

How does transport through membranes take place? Active transport a substance is moved against a concentration gradient Primary active transport: transport is linked to the hydrolysis of ATP or other high-energy molecule; for example, the Na+/K+ ion pump (Figure 8.24) Secondary active transport: driven by H+ gradient

How do membrane receptors work? oligomeric proteins binding of a biologically active substance to a receptor initiates an action within the cell

Lipid-Soluble Vitamins Vitamins are divided into two classes: lipid-soluble and water-soluble

How are prostaglandins related to lipids? Prostaglandins: a family of compounds that have the 20-carbon skeleton of prostanoic acid First detected in seminal fluid…from prostate The metabolic precursor is arachidonic acid (20 carbon atoms: 4 double bonds) Derived from fatty acids. Produced from arachidonic acid in several steps. Control of blood pressure, stimulation of smooth-muscle contraction and induction of inflammation. Aspirin inhibits synthesis of prostaglandins particularly in blood platelets – accounts for anti-inflammatory and fever reducing properties. Cortisone also inhibits synthesis of prostaglandins

How are leukotrienes related to lipids? Compounds also derived from arachidonic acid Found in white blood cells (leukocytes) Consists of 3 conjugated double bonds Constriction of smooth muscles, especially in the lungs Asthma attacks result from constricting action because synthesis of leukotriene C appears to be facilitated by allergic reactions – reaction to pollen

This project is funded by a grant awarded under the President’s Community Based Job Training Grant as implemented by the U.S. Department of Labor’s Employment and Training Administration (CB-15-162-06-60). NCC is an equal opportunity employer and does not discriminate on the following basis:  against any individual in the United States, on the basis of race, color, religion, sex, national origin, age disability, political affiliation or belief; and  against any beneficiary of programs financially assisted under Title I of the Workforce Investment Act of 1998 (WIA), on the basis of the beneficiary’s citizenship/status as a lawfully admitted immigrant authorized to work in the United States, or his or her participation in any WIA Title I-financially assisted program or activity.

Disclaimer This workforce solution was funded by a grant awarded under the President’s Community-Based Job Training Grants as implemented by the U.S. Department of Labor’s Employment and Training Administration.  The solution was created by the grantee and does not necessarily reflect the official position of the U.S. Department of Labor.  The Department of Labor makes no guarantees, warranties, or assurances of any kind, express or implied, with respect to such information, including any information on linked sites and including, but not limited to, accuracy of the information or its completeness, timeliness, usefulness, adequacy, continued availability, or ownership.  This solution is copyrighted by the institution that created it.  Internal use by an organization and/or personal use by an individual for non-commercial purposes is permissible.  All other uses require the prior authorization of the copyright owner.