Lipid Structure and Function (5)

MCAT Biochemistry Review 2025-2026

Insoluble; Soluble

lipids are _______ in water and _______ in nonpolar organic solvents

Phospholipids

are amphipathic and form the bilayer of biological membranes. They contain a hydrophilic (polar) head group and hydrophobic (nonpolar) tails

Phosphodiester Linkage

the head group of phospholipids is attached by this and, because it interacts with the environment, determines the function of the phospholipid

Saturation

this of the fatty acid tails determines the fluidity of the membrane

Less

saturated fatty acids are ______ fluid than unsaturated ones

Fatty Acids

form most of the structural thickness of the phospholipid bilayer

Glycerophospholipids

are phospholipids that contain a glycerol backbone

Sphingolipids

contain a sphingosine or sphingoid backbone

Sphingophospholipids

many (but not all) sphingolipids are also phospholipids, containing a phosphodiester bond

Sphingomyelins

are the major class of sphingophospholipids and contain a phosphatidylcholine or phosphatidylethanolamine head group. They are a major component of the myelin sheath

Glycosphingolipids

are attached to sugar moieties instead of a phosphate group

Cerebrosides

have one sugar connected to sphingosine

Globosides

have two or more sugars connected to sphingosine

Gangliosides

contain oligosaccharides with at least one terminal N-acetylneuraminic acid (NANA; also called sialic acid)

Waxes

contain long-chain fatty acids esterified to long-chain alcohols. They are used as protection against evaporation and parasites in plants and animals

Terpenes

are odiferous steroid precursors made from isoprene

Isoprene

a five-carbon molecule

Monoterpene

one terpene unit that contains two isoprene units

Terpenoids

are derived from terpenes via oxygenation or backbone rearrangement. They have similar odorous characteristics

Steroids

contain three cyclohexane rings and one cyclopentane ring. Their oxidation state and functional groups may vary

Steroid Hormones

have high-affinity receptors, work at low concentrations, and affect gene expression and metabolism

Cholesterol

is a steroid important to membrane fluidity and stability; it serves as a precursors to a host of other molecules

Prostaglandins

are autocrine and paracrine signaling molecules that regulate cAMP levels. They have powerful effects on smooth muscle contraction, body temperature, the sleep-wake cycle, fever, and pain

Vitamin A (Carotene)

is metabolized to retinal for vision and retinoic acid for gene expression in epithelial development

Vitamin D (cholecalciferol)

is metabolized to calcitriol in the kidneys and regulates calcium and phosphorous homeostasis in the intestines (increasing calcium and phosphate absorption), promoting bone formation

Rickets

caused by a deficiency of vitamin D

Vitamin E (Tocopherols)

act as biological antioxidants. Their aromatic rings destroy free radicals, preventing oxidative damage

Vitamin K (Phylloquinone and Menaquinones)

is important for formation of prothrombin, a clotting factor. It performs posttranslational modifications on a number of proteins, creating calcium-binding sites

Triacylglycerols (Triglycerides)

are the preferred method of storing energy for long-term use. They contain one glycerol attached to three fatty acids by ester bonds. The fatty acids usually vary within the same triacylglycerol

More

the carbon atoms in lipids are _______ reduced than carbohydrates, giving twice as much energy per gram during oxidation

Hydrophobic

triacylglycerols are very __________, so they are not hydrated by body water and do not carry additional water weight

Adipocytes

animals cells specifically used for storage of large triacylglycerol deposits

Free Fatty Acids

are unesterified fatty acids that travel in the bloodstream

Soaps

salts of free fatty acids are _____ and can be synthesized in saponification

Saponification

is the ester hydrolysis of triacylglycerols using a strong base, like sodium or potassium hydroxide

Surfactants

soaps act as _______, forming micelles

Micelle

can dissolve a lipid-soluble molecule in its fatty acid core, and washes away with water because of its shell of carboxylate head groups