1. Chapter Eight Lipids 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 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)

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
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 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)

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 • 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

40. Leukotrienes (Cont’d)