Chapter Eight Lipids and Proteins Are Associated in Biological Membranes

1. Chapter EightLipids and Proteins Are Associated in Biological Membranes

2. 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

3. 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

4. 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 _______________________

5. 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

6. 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)

7. 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 ______________________

8. 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 ____________________________

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

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

11. 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)

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

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

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

15. 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)

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

17. 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

18. 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

19. 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

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

21. 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)

22. 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 • ______________________________________ proteins • bound tightly to the interior of the membrane • can be removed by treatment with detergents or ultrasonification • removal generally denatures them

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

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

25. 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

26. Fluid Mosaic Model of Membrane Structure

27. 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

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

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

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

31. Lipid-Soluble Vitamins 2 classes of vitamins: __________________________________________

32. 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

33. Vitamin A • 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)

34. 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 ______________

35. 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

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

37. 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.

38. Arachodonic Acid and Some Prostoglandins

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

40. Leukotrienes (Cont’d)