Chapter Eight Lipids and Proteins Are Associated in Biological Membranes

What is a Lipid Lipids: a ___________________________ class of naturally occurring organic compounds classified together on the basis of common solubility properties insoluble in water, but soluble in aprotic organic solvents including ______________________________________ _______________________________ in nature Lipids include: Open Chain forms fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, glycolipids, lipid-soluble vitamins prostaglandins, leukotrienes, and thromboxanes Cyclic forms cholesterol, steroid hormones, and bile acids

Fatty Acids Fatty acid: an unbranched-chain carboxylic acid, most commonly of __________ carbons, derived from hydrolysis of animal fats, vegetable oils, or phosphodiacylglycerols of biological membranes In the shorthand notation for fatty acids the number of carbons and the number of double bonds in the chain are shown by two numbers, separated by a colon

Fatty Acids (Cont’d) Length of fatty acid plays a role in its _____________________ • Usually contain _________numbers of carbons (can contain ___________, depending on how they are biosynthesized) • FA that contain C=C, are ____________________: If contain only C-C bonds, they are _______________________

Fatty Acids (Cont’d) In most unsaturated fatty acids, the ______________ isomer predominates; the ______________ isomer is rare Unsaturated fatty acids have ____________ melting points than their saturated counterparts; the greater the degree of unsaturation, the _______________ the melting point

Triacylglycerols Triacylglycerol (triglyceride): an ester of ______________ with three __________________________ natural soaps are prepared by boiling triglycerides (animal fats or vegetable oils) with NaOH, in a reaction called _______________ (Latin, sapo, soap)

Soaps Soaps form water-insoluble salts when used in water containing Ca(II), Mg(II), and Fe(III) ions (____________________) Reactions with acids/bases as catalysts Salts formed by ______________________

Phosphoacylglycerols (Phospholipids) When one alcohol group of glycerol is esterified by a phosphoric acid rather than by a carboxylic acid, _________________________________ acid produced __________________ (phosphoglycerides) are the second most abundant group of naturally occurring lipids, and are found in plant and animal ____________________________

_________________________ A complex mixture of ___________________ of long-chain carboxylic acids and alcohols Found as protective coatings for plants and animals

Sphingolipids Contain _________________, a long-chain amino alcohol Found in plants and animals Abundant in ______________ system Structurally similar to ________________________

Glycolipids Glycolipid: a compound in which a _____________ is bound to an -OH of the lipid In most cases, sugar is either glucose or galactose many glycolipids are derived from ceramides Glycolipids with complex carbohydrate moiety that contains more than 3 sugars are known as ______________________ (Fig. 8.8, p. 207)

Steroids Steroids: a group of lipids that have a fused-ring structure of three _______________ rings, and one _______________ ring.

Sex Hormones synthesized in the ____________________ _____________________________: male sex hormones synthesized in the ____________________ responsible for the development of male secondary sex characteristics Testosterone _____________________________: female sex hormones responsible for the development of female secondary sex characteristics and control of the menstrual cycle (refer to Figure 8.9, p. 207)

Cholesterol The steroid of most interest in our discussion of ____________________________ is cholesterol

Biological Membranes Every cell has a cell membrane (plasma membrane) ___________________ cells also have membrane-enclosed organelles (nuclei, mitochondria…etc.) Molecular basis of membrane structure is in ____________ component(s): polar head groups are in contact with the _____________ environment nonpolar tails are buried within the _____________ the major force driving the formation of lipid bilayers is _______________________________ interaction the arrangement of hydrocarbon tails in the interior can be ______________ (if rich in saturated fatty acids) or __________________ (if rich in unsaturated fatty acids)

Lipid Bilayers The ___________ _____________ of the bilayer contains charged groups The ____________ _________ lie in the interior of the bilayer

Biological Membranes Plant membranes have a higher percentage of ___________ fatty acids than animal membranes The presence of cholesterol is characteristic of ___________ rather than _________ membranes __________________ membranes are less fluid (more rigid) than plant membranes The membranes of _________________, which contain no appreciable amounts of steroids, are the most fluid

Membrane Layers Both inner and outer layers of bilayer contain ____________ of lipids Compositions on inside and outside of lipid bilayer can be different This distinguishes the layers

Effect of Double Bonds on the Conformations of Fatty Acids ___________ in hydrocarbon chain Causes _________________ in packing against other chains This disorder causes __________________ in membranes with cis-double bonds vs saturated FA chains

Cholesterol reduces Fluidity Presence of cholesterol reduces fluidity by stabilizing _______________ _______________ _______________ of hydrocarbon tails of FA Due to ________________ interactions

Temperature Transition in Lipid Bilayer • With heat, membranes become more disordered; the transition temperature is _____________ for more rigid membranes; it is ______________ for less rigid membranes • _______________ of the lipid chains increases dramatically (Biochemical Connections p. 212)

Membrane Proteins Functions: transport substances across membranes; act as receptor sites, and sites of enzyme catalysis ______________________________________ proteins bound by electrostatic interactions can be removed by raising the ionic strength bound tightly to the interior of the membrane can be removed by treatment with detergents or ultrasonification removal generally denatures them

Membrane Proteins 1, 2, and 4 are integral proteins 3 is a peripheral protein

Proteins Can be Anchored to Membranes N-myristoyl- and S-palmitoyl ____________ motifs ____________ can be via N-terminal gly ____________ linkage with Cys

Fluid Mosaic Model Fluid: _________________ of components in the membrane; proteins, for example, “float” in the membrane and can __________________________________ Mosaic: components in the membrane exist ________________ as _____________________________ the structure is a lipid bilayer with proteins, glycolipids, and steroids such as cholesterol embedded in it no complexes, as for example, lipid-protein complexes, are formed

Fluid Mosaic Model of Membrane Structure

Membrane Function: Membrane Transport Passive transport driven by a ______________________________ 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 Active transport a substance is moved ___________________ 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

Facilitated Transport Passive diffusion of species (uncharged) across membrane, depends on ________________ & presence of carrier protein

Primary Active transport Movement of molecules against a gradient directly linked to hydrolysis of high-energy yielding molecule (e.g. _________)

Membrane Receptors Membrane receptors generally _____________ proteins binding of a biologically active substance to a receptor initiates an action within the cell

Lipid-Soluble Vitamins 2 classes of vitamins: __________________________________________

Vitamin A Vitamin A (retinol) occurs only in ______________________ Extensively unsaturated hydrocarbon (-carotene) Vitamin A is found in the plant world in the form of a provitamin in a group of pigments called ______________ enzyme-catalyzed cleavage of -carotene followed by reduction gives two molecules of vitamin A

Vitamin A the active molecule is ________ (vitamin A aldehyde) The best understood role of vitamin A is its participation in the visual cycle in rod cells the active molecule is ________ (vitamin A aldehyde) retinal forms an imine with an -NH2 group of the protein opsin to form the visual pigment called __________________________________ the primary chemical event of vision in rod cells is absorption of light by rhodopsin followed by ____________________________________ of the 11-cis double bond to the 11-trans double bond (Biochemical Connections, p. 225)

Vitamin D A group of structurally related compounds that are involved in the regulation of ________________ and ________________ metabolism the most abundant form in the circulatory system is ______________

Vitamin E The most active vitamin E is _______________________ Vitamin E is an _____________________; traps HOO• and ROO• radicals formed as a result of oxidation by O2 of unsaturated hydrocarbon chains in membrane phospholipids

Vitamin K Vitamin K has an important role in the _____________ process Long unsaturated hydrocarbon side chain consists of repeating ____________ units

Prostaglandins Prostaglandins: a family of compounds that have the _________________________________ of prostanoic acid First detected in seminal fluid…from __________________ The metabolic precursor is ______________________ acid (20 carbon atoms: 4 double bonds) Production of prostaglandins from arachidonic acid occurs in several steps.

Arachodonic Acid and Some Prostoglandins

Leukotrienes • Found in _____________________________ • Compounds also derived from arachidonic acid • Found in _____________________________ • Consists of 3 _________________ double bonds • An important property is constriction of _________ ________________, especially in the lungs

Leukotrienes (Cont’d)