Chapter 10.3: Lipids as Signals, Cofactors, and Pigments CHEM 7784 Biochemistry Professor Bensley

CHAPTER 10.3 Signaling Lipids Today’s Objectives: To learn and understand the Biological roles of lipids Structure and properties of signaling lipids

Steroid Hormones Steroids are oxidized derivatives of sterols Steroids have the sterol nucleus, but lack the alkyl chain found in cholesterol. This makes them more polar than cholesterol. Steroid hormones are synthesized in gonads and adrenal glands from cholesterol They are carried through the body in the blood stream, usually attached to carrier proteins Many of the steroid hormones are male and female sex hormones

FIGURE 10-19 Steroids derived from cholesterol FIGURE 10-19 Steroids derived from cholesterol. Testosterone, the male sex hormone, is produced in the testes. Estradiol, one of the female sex hormones, is produced in the ovaries and placenta. Cortisol and aldosterone are hormones synthesized in the cortex of the adrenal gland; they regulate glucose metabolism and salt excretion, respectively. Prednisolone and prednisone are synthetic steroids used as antiinflammatory agents. Brassinolide is a growth regulator found in vascular plants.

Signaling Lipids Paracrine lipid hormones are are present in small amounts but play vital roles as signaling molecules between nearby cells Enzymatic oxidation of arachidonic acid yields prostaglandins, thromboxanes, and leukotrienes

Arachidonic Acid Derivatives as Signaling Lipids Variety of functions: Inflammation and fever (prostaglandins) Formation of blood clots (thromboxanes) Smooth muscle contraction in lungs (leukotrienes) Smooth muscle contraction in uterus (prostaglandins)

FIGURE 10-18 Arachidonic acid and some eicosanoid derivatives FIGURE 10-18 Arachidonic acid and some eicosanoid derivatives. Arachidonic acid (arachidonate at pH 7) is the precursor of eicosanoids, including the prostaglandins, thromboxanes, and leukotrienes. In prostaglandin E1, C-8 and C-12 of arachidonate are joined to form the characteristic five-membered ring. In thromboxane A2, the C-8 and C-12 are joined and an oxygen atom is added to form the six-membered ring. Leukotriene A4 has a series of three conjugated double bonds. Nonsteroidal antiinflammatory drugs (NSAIDs) such as aspirin and ibuprofen block the formation of prostaglandins and thromboxanes from arachidonate by inhibiting the enzyme cyclooxygenase (prostaglandin H2 synthase).

Chapter 10: Summary In this chapter, we learned that: lipids are a structurally and functionally diverse class of molecules that are poorly soluble in water triacylglycerols are the main storage lipids phospholipids are the main constituents of membranes sphingolipids play roles in cell recognition cholesterol is both a membrane lipid and the precursor for steroid hormones some lipids carry signals from cell to cell and from tissue to tissue