Lipids, Cell Membranes, Hormones, and Fat-Soluble Vitamins – Chapter 19

These flashcards cover the key definitions, structures, functions, and health connections of lipids, cell membranes, steroid hormones, fat-soluble vitamins, and eicosanoids as outlined in Chapter 19.

What physical property defines lipids?

They are soluble in organic solvents and insoluble in water.

Into which two broad classes are lipids divided based on hydrolysis?

Hydrolyzable lipids and non-hydrolyzable lipids.

What functional group do fatty acids contain?

A carboxylic acid group (RCOOH).

How many carbon atoms are most common in naturally occurring fatty acids?

12–20 carbons, and they usually have an even number.

What is the difference between saturated and unsaturated fatty acids?

Saturated fatty acids contain no C=C double bonds; unsaturated fatty acids contain one or more (usually cis) C=C double bonds.

How does increasing the number of double bonds affect a fatty acid’s melting point?

More double bonds lower the melting point.

Name a common saturated fatty acid with 18 carbons.

Stearic acid.

Name a common monounsaturated fatty acid with 18 carbons.

Oleic acid.

Why is linoleic acid called an omega-6 fatty acid?

Its first double bond is six carbons from the methyl (omega) end.

Why is linolenic acid called an omega-3 fatty acid?

Its first double bond is three carbons from the methyl (omega) end.

What is the general structural formula of a wax?

An ester formed from a long-chain fatty acid and a high-molecular-weight alcohol.

Give one biological role of waxes.

They form protective, hydrophobic coatings on feathers, wool, and beeswax.

What reaction converts a wax back to its fatty acid and alcohol?

Acid- or base-catalyzed hydrolysis.

What are triacylglycerols (triglycerides)?

Triesters of glycerol with three fatty acids.

Differentiate simple and mixed triacylglycerols.

Simple triacylglycerols have three identical fatty acid chains; mixed triacylglycerols contain two or three different fatty acids.

Why are animal fats usually solid at room temperature?

They are richer in saturated fatty acids, giving higher melting points.

Why are vegetable oils liquid at room temperature?

They contain more unsaturated fatty acids, lowering melting points.

How do trans fats affect blood cholesterol?

They raise LDL and act like saturated fats, increasing heart-disease risk.

What percentage of daily calories is recommended to come from lipids?

No more than 20–35 %.

Where are triacylglycerols stored in the human body?

In adipose cells beneath the skin, in the breast area, and around internal organs.

Which enzymes hydrolyze triacylglycerols during metabolism?

Lipases.

What products result from complete metabolism of triacylglycerols?

CO₂, H₂O, and large amounts of energy.

What is saponification?

Basic hydrolysis of triacylglycerols to produce soap (metal salts of fatty acids).

How do soaps clean grease?

Their nonpolar tails dissolve grease, while polar heads render it water-soluble.

What elements make up phospholipids?

They contain C, H, O, and at least one phosphorus atom.

Name the two major classes of phospholipids.

Phosphoacylglycerols and sphingomyelins.

What replaces the third fatty acid in a phosphoacylglycerol?

A phosphodiester linked to an alcohol (e.g., choline or ethanolamine).

Give an example of a phosphoacylglycerol containing choline.

Lecithin (phosphatidylcholine).

What backbone does a sphingomyelin contain?

A sphingosine backbone.

How is the fatty acid attached in sphingomyelin?

By an amide bond to sphingosine.

In what biological structure are sphingomyelins especially abundant?

The myelin sheath surrounding nerve cells.

Describe the arrangement of phospholipids in water.

They form a lipid bilayer with polar heads outward and nonpolar tails inward.

What is meant by a cell membrane being ‘selectively permeable’?

It allows some substances to pass while blocking others.

Differentiate peripheral and integral membrane proteins.

Peripheral proteins are embedded on one side; integral proteins span the entire bilayer.

Which transport process moves molecules from high to low concentration without energy?

Simple diffusion.

What is facilitated transport?

Movement of larger polar molecules through protein channels down a concentration gradient.

Define active transport.

Energy-requiring movement of ions or molecules against a concentration gradient via membrane proteins.

What class of lipids does cholesterol belong to?

Steroids.

Where is cholesterol synthesized?

In the liver.

Which lipoproteins carry cholesterol from liver to tissues?

Low-density lipoproteins (LDLs).

Which lipoproteins return excess cholesterol to the liver?

High-density lipoproteins (HDLs).

Why is LDL called “bad” cholesterol?

It deposits cholesterol on artery walls, forming plaque.

Why is HDL considered “good” cholesterol?

It removes excess cholesterol from the bloodstream.

State the recommended healthy serum cholesterol levels.

HDL > 40 mg/dL, LDL < 100 mg/dL, total < 200 mg/dL.

How do statin drugs lower cholesterol?

They block an early step in cholesterol biosynthesis.

Define a hormone.

A molecule synthesized in one part of an organism that triggers a response at another site.

Name the primary female sex hormones.

Estrogens (estradiol, estrone) and progestin (progesterone).

What is the primary role of progesterone?

Preparation of the uterus for implantation of a fertilized egg.

Name two major male sex hormones.

Testosterone and androsterone.

What are anabolic steroids?

Synthetic androgen analogues that promote muscle growth.

Give one risk of prolonged anabolic-steroid use.

It can cause severe physical and psychological side effects (e.g., liver damage, aggression).

What are the three adrenal cortical steroids highlighted in the notes?

Aldosterone, cortisone, and cortisol.

What is the function of aldosterone?

Regulates blood pressure and volume by controlling Na⁺ and K⁺ levels.

What medical use do cortisone and cortisol share?

They act as anti-inflammatory agents and influence carbohydrate metabolism.

List the four fat-soluble vitamins.

Vitamins A, D, E, and K.

What deficiency disease is caused by lack of vitamin A?

Night blindness (and dry eyes/skin).

Which vitamin regulates calcium metabolism and prevents rickets?

Vitamin D.

What is the chief role of vitamin E?

It serves as an antioxidant protecting unsaturated fatty acids from oxidation.

Which vitamin is essential for synthesis of clotting proteins?

Vitamin K.

What are eicosanoids?

Potent local mediators such as prostaglandins and leukotrienes, synthesized on demand.

Name two key enzymes involved in prostaglandin synthesis.

Cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2).

How do NSAIDs like aspirin reduce inflammation?

They inhibit both COX-1 and COX-2, blocking prostaglandin synthesis.

Why were drugs like Vioxx and Celebrex developed?

To selectively inhibit COX-2, reducing inflammation without harming the stomach lining.

What role do leukotrienes play in asthma?

They constrict bronchial smooth muscle, contributing to asthma attacks.

How do new asthma drugs target leukotrienes?

They block leukotriene synthesis, treating the underlying cause rather than symptoms.