chapter 12. part i. lipids - personal.tcu.edupersonal.tcu.edu/yryu/50133/lipids.pdfcarboxylic acids...
TRANSCRIPT
Chapter 12.
Part I. Lipids
Functions of lipids
• Building blocks of membranes• Energy storage• Hormones• Mediators of signal transduction
Lipid classification
• Fatty acids• Triacylglycerols• Glycerophospholipids• Sphingolipids• Steroids• Other lipids
Fatty acidsCarboxylic acids with long-chain hydrocarbon side groups
• Saturated• Unsaturated - double bonds are usually in the cis configuration;
30° bend in the hydrocarbon chain
18:0 18:1 (∆9) 18:2 (∆9,12) 18:3 (∆9,12,15)
ω-3 fatty acidω-6 fatty acid
ω1
2
34
56
1ω
23
Structural features of storage and membrane lipids
Triacylglycerols (Triglycerides)• Triesters of glycerol and fatty acids• Fats or oils• Energy storage and thermal insulation
Trans fats
Strong contributing factor of coronary heart disease
(↑LDL, ↓HDL)
Major food sources for trans fat for American adults
FDA “Trans Fatty Acids in Nutrition Labeling, Nutrient Content Claims, and Health Claims” (July 11, 2003)
Adipocytes (Fat cells)• Synthesis and storage of fats• Secretion of protein hormones in related to the glucose
homeostasis (adiponectin, leptin, resistin etc)
Glycerophospholipids
• Amphiphilic• Major lipid
components of biological membranes
• Signal transduction
tail
head
Phospholipids are hydrolyzed by phospholipases
Sphingolipids
Sphingosine
• Glycolipids• Abundant in brain and nerve membranes• Cell-cell recognition
Steroids
CholesterolSteroid core structure
Cholesteryl esters
Functions of steroids
• Component of membranes– cholesterol
• Bile acids (helping digestion of dietary fats)– Cholic acid and glycocholic acid
• Hormones– estrogens– androgens– progestins– glucocorticoids– mineralocorticoids
Cholesterol
• Membrane component• Precursor of steroid
hormones• Precursor of bile salts
Steroid hormones
Bile acids
Phytosterols
Vitamin D
Inactive
Enzymatic hydroxylation
This active form promotes the intestinal absorption of dietary Ca2+, thereby increases serum [Ca2+] and subsequently the deposition of Ca2+ in bones and teeth
Other fat-soluble vitamins
(Photoreceptor in the eye)(Electron transfer in mitochondria)
(Blood clotting)
(Antioxidant of membrane proteins and lipids)
Isoprenoids (=terpenoids)
(citrus fruits) (vitamin A precursor)
(plant hormone)
(precursor of plant and animal steroids)
(antioxidant)
Eicosanoids
• Derived from arachidonic acid (C20)• Prostaglandins, thromboxanes and
Leukotrienes• Regulate pain, fever, blood pressure,
blood coagulation, and reproduction• Produced and act locally at low
concentrations (10-12 to 10-14M)• Short lifetimes (seconds to minutes)
(Cyclooxygenase, COX)
Arachidonate pathway
COX Enzymes
• COX-1– Constitutive, expressed in most tissues– Cell maintenance and housekeeping– Synthesis of prostaglandins responsible for
protection of the stomach lining• COX-2
– Induced by inflammatory stimuli such as injury or disease
– Synthesis of prostaglandins responsible for pain and inflammation
Non-steroidal anti-inflammatory drugs (NSAIDs)
Selective inhibitor of Cox-2
Inhibitors of Cox-1 and Cox-2
(Tylenol)
(Advil, Motrin)
Little anti-inflammatory effect