biochem chapter 5 & 6 lipids and DNA

Lipids — solubility

Insoluble in water; soluble in nonpolar solvents

Amphipathic

Having both a hydrophilic (polar) and hydrophobic (nonpolar) region; describes phospholipids

Phospholipid structure

Hydrophilic polar head group attached via a phosphodiester linkage, and two hydrophobic fatty acid tails

Role of head group in phospholipids

The head group attached to the phosphodiester linkage determines the function of the phospholipid

Membrane fluidity and fatty acid saturation

Saturated fatty acid tails → less fluid membrane; unsaturated fatty acid tails → more fluid membrane

Glycerophospholipids

Phospholipids that contain a glycerol backbone

Sphingolipids

Lipids with a sphingosine or sphingoid backbone instead of glycerol

Sphingophospholipids

Sphingolipids that contain a phosphodiester bond; a subclass of both sphingolipids and phospholipids

Sphingomyelins

Major class of sphingolipids; contain a phosphatidylcholine or phosphatidylethanolamine head group; major component of the myelin sheath

Glycosphingolipids

Sphingolipids attached to sugar moieties instead of a phosphate group

Cerebrosides

Glycosphingolipids with one sugar connected to sphingosine

Globosides

Glycosphingolipids with two or more sugars connected to sphingosine

Gangliosides

Glycosphingolipids containing oligosaccharides with at least one terminal N-acetylneuraminic acid

Waxes

Long-chain fatty acids esterified to long-chain alcohols; protect against water evaporation and parasites in plants and animals

Terpenes

Odiferous steroid precursors built from isoprene, a 5-carbon molecule

Monoterpene

A terpene containing 2 isoprene units (10 carbons total)

Terpenoids

Derived from terpenes via oxygenation or backbone rearrangement; share similar odorous characteristics

Steroid ring structure

Three cyclohexane rings fused to one cyclopentane ring

Steroid hormones

High-affinity receptors; work at low concentrations; affect gene expression and metabolism

Cholesterol

A steroid critical for membrane fluidity and stability; serves as a precursor to many other molecules including steroid hormones

Prostaglandins

Autocrine and paracrine signaling lipids that regulate cAMP levels; affect smooth muscle contraction, body temperature, the sleep-wake cycle, fever, and pain

Fat-soluble vitamins

Vitamins A, D, E, and K — stored in fat tissue and require lipids for absorption

Vitamin A (carotene)

Metabolized to retinal (required for vision) and retinoic acid (regulates gene expression in epithelial development)

Vitamin D (cholecalciferol)

Metabolized to calcitriol in the kidneys; regulates calcium and phosphorus homeostasis in the intestines, promoting bone formation

Vitamin D deficiency

Causes rickets (soft, weakened bones)

Vitamin E (tocopherols)

Biological antioxidants; aromatic rings neutralize free radicals, preventing oxidative damage

Vitamin K (phylloquinone & menaquinones)

Required for formation of prothrombin (a clotting factor); performs posttranslational modifications that create calcium-binding sites on proteins

Triacylglycerols (triglycerides)

The preferred method of long-term energy storage; one glycerol backbone esterified to 3 (different) fatty acids

Why lipids store more energy than carbohydrates

Carbon atoms in lipids are more reduced than in carbohydrates, yielding roughly twice as much energy per gram upon oxidation

Why triacylglycerols are efficient for storage

They are highly hydrophobic and not hydrated by body water, so they carry no additional water weight

Adipocytes

Animal cells specialized for storing large deposits of triacylglycerols

Free fatty acids

Unesterified fatty acids that circulate in the bloodstream; their salts are soaps

Saponification

Ester hydrolysis of a triacylglycerol using a strong base (NaOH or KOH) to produce soap (fatty acid salts) and glycerol

Soaps as surfactants

Soaps form micelles — lipid-soluble molecules are dissolved in the hydrophobic fatty acid core, and the whole structure washes away in water due to the outer hydrophilic carboxylate head groups

Micelle

Spherical structure formed by soap molecules in water; hydrophobic core traps lipid-soluble molecules; hydrophilic shell is water-solubl