Quiz - Lipids - 2 | Lipids

Organic Chemistry 3 - Quiz - Lipids - 2


Which of the following statements about fatty acids is correct in the context of their role in triglyceride structure and function?

Fatty acids can indeed be either saturated or unsaturated. Unsaturated fatty acids contain double bonds which create kinks, preventing tight packing and hence making the triglyceride more likely to be liquid at room temperature, like oils. Saturated fatty acids, which lack double bonds, are normally solid at room temperature, like fats.


What is the primary chemical reaction through which triglycerides are formed, and what is its significance?

Triglycerides are formed through an esterification reaction, where each of glycerol's hydroxyl (OH) groups reacts with the carboxyl group (COOH) of a fatty acid to form an ester bond. This is a dehydration synthesis reaction, which is crucial for the storage and release of metabolic energy as needed by an organism.


Which structural feature of phospholipids is most critical for their function in forming biological membranes?

Phospholipids have an amphipathic character, which means they have hydrophobic tails (the fatty acid chains) and hydrophilic heads (the phosphate-containing group). This amphipathic nature allows them to arrange themselves into a bilayer that forms the fundamental structure of all cell membranes. The hydrophilic heads face outward to interact with water, while the hydrophobic tails face inward, away from water, which is key to membrane functionality.


Which of the following is not a biological function of steroids?

Steroids such as cholesterol are not used for energy storage; that role is typically reserved for fats, specifically triglycerides. Steroids are instead precursors to several significant hormones and vitamins, they modulate cell membrane properties, and some, like steroid hormones, serve as signaling molecules. Their structure is not suitable for energy storage, unlike the long hydrocarbon chains found in triglycerides.


In the context of eicosanoids, such as prostaglandins, what is their primary role in the body?

Eicosanoids, which include prostaglandins, thromboxanes, and leukotrienes, are signaling molecules derived from fatty acids. They have wide-ranging roles in the body's physiology, including the regulation of inflammation, pain, fever, blood pressure, blood clot formation, and immune function. Unlike triglycerides or waxes, eicosanoids are not used for energy storage or structural purposes.


Why are waxes typically solid at room temperature and highly hydrophobic?

Waxes are comprised of esters formed from long-chain alcohols and fatty acids. These long hydrocarbon chains can tightly pack together, enhancing van der Waals forces and making waxes solid at room temperature. Their chemical structure lacks polar groups capable of forming hydrogen bonds with water, thus waxes are highly hydrophobic.


When comparing the properties of triglycerides and phospholipids, what distinguishes these two classes of lipids in biological membranes?

Phospholipids are unique in that they contain a hydrophilic 'head' region, which includes a phosphate group, and a hydrophobic 'tail' region, consisting of two fatty acid chains. This structural distinction allows them to form the lipid bilayer of biological membranes, with the hydrophilic heads facing outward and the hydrophobic tails facing inward, away from the aqueous environment, creating a selective barrier. Triglycerides, in contrast, are primarily used for energy storage and do not play a role in membrane structure.


Which of the following is not a typical role of terpenes?

Terpenes are a diverse class of naturally occurring organic compounds primarily known for their roles in plant biochemistry, such as serving as pigments in photosynthesis (e.g., carotenoids), acting as biochemical precursors (e.g., to steroids), and as part of plant defenses. However, terpenes are not typically associated with providing structural integrity to cell membranes, which is a role more closely associated with phospholipids and cholesterol.


In the formation of eicosanoids from fatty acids, which enzyme class is primarily responsible for catalyzing the production of prostaglandins?

Cyclooxygenase (COX) and lipoxygenase (LOX) enzymes are responsible for the oxygenation of arachidonic acid, a key step in the biosynthesis of eicosanoids. COX enzymes catalyze the formation of prostaglandins and thromboxanes, while LOX enzymes are involved in the production of leukotrienes. These enzymes are critical in the pathway of eicosanoid synthesis, which affects inflammation and other cellular processes.


What is the general structural feature of terpenes?

Terpenes are composed of repeating isoprene units, which are five-carbon building blocks containing a double bond.