Ch 10 Lipids Biochem

Lipids

A diverse group of hydrophobic (water-insoluble) molecules that do not mix well with water.

Energy Storage

Lipids are used for energy storage due to the highly reduced nature of fatty acids, making them rich in chemical energy.

Membrane Structure

Lipids are used for membrane structure, characterized by a polar head and hydrophobic tails.

Cellular Functions of Lipids

Lipids serve other functions such as cellular messengers, hormones, electron carriers, or pigments.

Chemical Properties of Lipids

The chemical properties of lipids are related to their structure.

Fatty Acids

Carboxylic acids with hydrocarbon tails, ranging from 4 to 36 carbons, can be saturated or unsaturated.

Saturated Fatty Acids

Fatty acids with no double bonds.

Unsaturated Fatty Acids

Fatty acids with one or more double bonds, usually in the cis configuration.

Naming Fatty Acids

Chain length and number of double bonds are separated by a colon, for example, 18:2 indicates 18 carbons and 2 double bonds.

Solubility of Fatty Acids

Fatty acids are poorly soluble in water due to nonpolar hydrocarbon chains; increased chain length or decreased double bonds further decrease solubility.

Melting Point of Fatty Acids

Saturated fatty acids are waxy at room temperature, while unsaturated fatty acids are oily liquids.

Triacylglycerols (Triglycerides)

Three fatty acids linked to a glycerol molecule through ester linkages, used for energy storage.

Energy Yield of Triacylglycerols

More reduced than sugars, yielding more energy upon oxidation and stored without water for efficient energy storage.

Storage of Triacylglycerols

Stored in adipocytes (fat cells) in animals and seeds in plants.

Insulation from Triacylglycerols

Provide insulation for warm-blooded polar animals and hibernating animals.

Trans Fats

Dietary trans fatty acids linked to cardiovascular disease by raising triglycerides and 'bad' cholesterol (LDL) while lowering 'good' cholesterol (HDL).

Membrane Lipids

Characterized by hydrophobic tails attached to polar head groups.

Phospholipids

Contain a phosphate group, hydrophobic fatty acid tails, and a glycerol or sphingosine backbone.

Glycerophospholipids

Two fatty acids attached to glycerol, with a polar group attached via a phosphodiester linkage.

Ether Lipids

One fatty acid chain linked to glycerol via an ether linkage rather than an ester linkage.

Sphingolipids

Have a sphingosine backbone instead of glycerol.

Ceramides

A fatty acid attached to sphingosine.

Sphingomyelins

Contain phosphocholine or phosphoethanolamine head groups.

Glycosphingolipids

Have sugar head groups but do not contain phosphate.

Gangliosides

Have oligosaccharide head groups with sialic acid residues.

Sterols

Characterized by a rigid system of four fused hydrocarbon rings.

Eicosanoids

Derived from arachidonic acid, include prostaglandins, thromboxanes, leukotrienes, and lipoxins.

Prostaglandins (PG)

Contain a five-carbon ring; involved in inflammation, pain, fever, blood flow, and smooth muscle contraction.

Steroid Hormones

Oxidized derivatives of sterols; regulate gene expression.

Vitamins A, D, E, and K

Fat-soluble vitamins.

Vitamin A

Important for development, cell growth, vision, can be stored in the body.

Vitamin D

Important for bone formation.

Vitamin E

Act as biological antioxidants.

Vitamin K

Involved in blood clotting.

Ubiquinone and Plastoquinone

Lipophilic electron carriers in ATP synthesis.

Natural Pigments

Contain conjugated dienes that absorb visible light.

Biological Membranes

A double layer (bilayer) of lipids that acts as a barrier to polar molecules and ions.

Amphipathic

Having both hydrophobic and hydrophilic regions.

Micelles

Spherical structures where hydrophobic regions are in the interior and hydrophilic heads are on the exterior.

Bilayers

Two-dimensional sheets with two lipid monolayers.

Vesicles (liposomes)

Bilayer sheets that form hollow spheres.

Membrane functions

Permit shape changes, exocytosis/endocytosis, serve as gatekeepers.

Lipid Composition

Varies between different membranes.

Membrane trafficking

Lipids and proteins synthesized in the ER move to their destination organelles or to the plasma membrane.

Lipid composition changes during trafficking

Sphingolipids and cholesterol largely replace phosphatidylcholine in the plasma membrane.

Sphingolipids as Messengers

Ceramide and sphingomyelin regulate protein kinases, cell division, differentiation, migration, and programmed cell death.

Sterols as Precursors

Serve as precursors for steroid hormones and bile acids.

Bile Acids

Polar derivatives of cholesterol that emulsify dietary fats for digestion.

Volatile Lipids

Many volatile, lipophilic compounds derived from fatty acids or isoprene units function as signals to attract pollinators, repel herbivores, attract organisms that defend the plant against herbivores, and communicate with other plants.

Vitamins

Essential compounds that cannot be synthesized by the body.

Lipid Quinones

Act as oxidation-reduction cofactors.

Natural Pigments

Conjugated dienes with alternating single and double bonds that can absorb light.