Richmond Christian School Anatomy & Physiology 12 Lesson 3: Lipids

A comprehensive set of practice flashcards covering lipid classes (triglycerides, phospholipids, steroids, waxes), fatty acid structure and saturation, health effects, and lipoprotein transport.

Why are lipids classified as hydrophobic?

Lipids are non-polar molecules, meaning they do not mix with polar solvents such as water.

How much energy do lipids provide per gram compared to carbohydrates and protein?

Lipids provide $9\,\text{kcal}$ per gram, which is more than double the $4\,\text{kcal}$ per gram provided by carbohydrates and protein.

What are the four major structural categories of lipids?

Triglycerides (neutral fats), phospholipids, steroids, and waxes.

Which major class of lipids is the exception to being built from fatty acid chains?

Steroids, which are built from fused carbon rings rather than fatty acid chains.

What is the general chemical structure of a fatty acid?

A long hydrocarbon ($\text{C–H}$) chain with a carboxylic acid group ($-\text{COOH}$) at one end.

What structural and physical characteristics distinguish saturated from unsaturated fatty acids?

Saturated fatty acids contain no $\text{C=C}$ double bonds, are solid at room temperature, and are common in animal fats. Unsaturated fatty acids contain one or more $\text{C=C}$ double bonds, are liquid at room temperature, and are common in plant and fish oils.

What are the two essential fatty acids that must be obtained through the diet?

Linoleic acid (omega-6) and alpha-linolenic acid (omega-3).

What signaling molecules are formed from essential fatty acids, and what physiological processes do they regulate?

They are precursors to eicosanoids, which regulate inflammation, blood pressure, and blood clotting.

How are trans fats structurally arranged, and how are they mostly manufactured?

Trans fats are unsaturated fats where the double bond holds hydrogen atoms on opposite sides of the chain ("trans") instead of the natural "cis" shape; they are mostly created by partially hydrogenating vegetable oils.

Why are trans fats considered the least healthy dietary fats?

They cause a double hit by simultaneously raising LDL ("bad") cholesterol and lowering HDL ("good") cholesterol.

How are triglycerides assembled through dehydration synthesis?

One glycerol molecule binds to $3$ fatty acids through ester bonds, releasing $3$ water molecules.

What are the primary biological roles of triglycerides in the human body?

They act as the body's main energy-storage molecule (stored as adipose tissue), cushion internal organs, and provide insulation against temperature change.

By what chemical process are stored triglycerides broken down to release fatty acids for energy?

Hydrolysis.

What structural feature makes a phospholipid amphipathic?

One fatty acid of a triglyceride is replaced by a polar, hydrophilic phosphate head (often paired with choline), while the remaining two fatty acid tails remain nonpolar and hydrophobic.

How do phospholipids arrange themselves when surrounded by water?

They self-assemble into a bilayer with hydrophilic heads facing the watery exterior and interior environments, shielding the hydrophobic fatty acid tails in the middle.

What class of lipid is represented by the four fused rings shown in this diagram?

A steroid (composed of three six-membered rings and one five-membered ring).

What is the parent steroid molecule used to synthesize sex hormones, adrenal hormones, and vitamin D?

Cholesterol.

What physiological functions are regulated by the adrenal hormones cortisol and aldosterone?

Cortisol regulates blood sugar and metabolism, while aldosterone regulates sodium and water balance.

What role does cholesterol serve directly within the cell membrane?

It is embedded into the phospholipid bilayer to help control membrane fluidity.

What chemical constituents make up a wax molecule?

An ester formed from a long-chain fatty acid linked to a long-chain alcohol (instead of glycerol).

What are biological examples of waxes and their function in living organisms?

Examples include earwax (cerumen) in the ear canal, beeswax, lanolin (wool grease), and the waxy cuticle on plant leaves; they provide extremely hydrophobic, waterproof, and protective coatings.

How are hydrophobic lipids structured inside a lipoprotein for transport through watery blood?

A lipoprotein has an outer shell composed of phospholipids and proteins, enclosing an interior core that carries cholesterol and triglycerides.

What are the opposing functions of LDL and HDL in the transport of cholesterol?

LDL (low-density lipoprotein) transports cholesterol from the liver to cells and can accumulate in artery walls, whereas HDL (high-density lipoprotein) carries excess cholesterol from cells back to the liver for removal.