1. Lipids and Proteins Are Associated in Biological Membranes
Chapter 8

2. 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

3. 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

4. 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)

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

6. 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

7. 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

8. 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

9. 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

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

11. 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

12. 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

13. 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

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

15. 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

16. 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

17. 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

18. 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.

19. 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

20. 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

21. 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.

22. 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

23. 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

24. 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

25. 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

26. Fluid Mosaic Model of Membrane Structure

27. 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

28. 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

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

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

31. 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

32. 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

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