Biochemistry of Lipids and Hormones

Introduction to Lipids

• Lipids are a diverse group of water-insoluble organic molecules.
• Their insolubility in water leads to compartmentalization within the body.
• Membrane-associated lipids exist.
• Lipid droplets (TAGs) are found in adipocytes.
• Lipids are transported in plasma by lipoprotein particles.

Structural Relationship of Lipids

• Lipids are categorized into groups based on their structure.
• Simplest lipids include eicosanoids, which are derived from fatty acids (FAs).
• Other major lipid classes are illustrated.
• These categories include triacylglycerols, waxes, steroids, lipid vitamins, terpenes, isoprenoids, glycerophospholipids, sphingolipids, ceramides, sphingomyelins, and glycosphingolipids, among others.
• Phospholipids have a unique classification of subgroups.

Functions of Lipids

• Lipids are a major energy source.
• Lipids form hydrophobic barriers.
• Lipids include fat-soluble vitamins.
• Lipids have coenzyme functions.
• Lipids include hormones, such as steroids and prostaglandins.
• Lipids protect vital organs.
• Lipids act as carriers for vitamins and suppress hunger.

Dietary Lipids

• Adults typically ingest approximately 81 grams of lipids daily.
• A substantial portion (over 90%) is usually composed of triacylglycerols (TAGs).
• Other dietary lipids include cholesterol, cholesterol esters, phospholipids, and free fatty acids.

Common Lipids

• Diverse structural examples of important lipid molecules are included.
• Important examples of fatty acids, triacylglycerols, phospholipids, steroids, and glycolipids are illustrated.
• Illustrations show the hydrophobic portions of the molecules.

Fatty Acids

• Fatty acids are amphipathic molecules.
• They comprise a hydrophobic hydrocarbon tail and a terminal carboxyl group.
• The length of the hydrocarbon tail influences the molecule's hydrophobicity.
• Saturated fatty acids lack double bonds.
• Unsaturated fatty acids contain one or more double bonds, usually in the cis configuration.
• Cis bonds result in kinks in the fatty acid tails.

Fatty Acid Functions

• Fatty acids (FAs) can be oxidized by tissues, mainly liver and muscle, to produce energy.
• The liver uses fatty acids to produce ketone bodies.
• Fatty acids are structural components of membrane lipids (phospholipids and glycolipids).
• Fatty acids act as signaling molecules.
• Esterified FAs are the major energy reservoir in adipose tissue.
• FAs serve as the precursors for hormone-like prostaglandins.

Fatty Acid Saturation

• Saturated fatty acids lack double bonds.
• Unsaturated fatty acids contain one or more double bonds.
• Unsaturated fatty acids typically include cis double bonds.
• Cis double bonds create a kink in the fatty acid tail, affecting membrane fluidity.
• Changes in fatty acid composition alter membrane fluidity.

Fatty Acid Length and Position of Double Bonds

• Specific fatty acids like stearic, oleic, linoleic, and α-linolenic acids are detailed in terms of carbon number and degree of unsaturation.
• The structural formula examples reflect the cis configuration of double bonds.

Lipid Chain Length and Position

• Fatty acids with different chain lengths are important in the human body.
• In humans, fatty acids with 16, 18, and 20 carbons predominate.
• Fatty acids with more than 22 carbons are typically found in the brain.
• The attachment to the carboxyl group defines the α-carbon.
• The terminal methyl group defines the ω-carbon.
• Double bonds' position is denoted relative to the ω-end.

Triacylglycerols (TAGs)

• TAGs are complex lipids, composed of three fatty acids and one glycerol molecule.
• TAGs are the main form of stored energy in adipose tissue.
• TAGs are primarily stored as nearly anhydrous oily droplets in adipose tissue.

Phospholipids

• Phospholipids are polar, ionic compounds.
• They have an alcohol group attached to diacylglycerol or sphingosine.
• They have a hydrophilic head and a hydrophobic tail.
• They are amphipathic.
• Two major classes: glycerophospholipids and sphingophospholipids.
• Phospholipids are vital components of cell membranes.

Phospholipids (PLs) Location

• PLs are the predominant lipids in cell membranes.
• Phospholipids are also found in lung surfactant and bile.

Phospholipid Structure

• Two main types: glycerophospholipids and sphingophospholipids.
• Glycerophospholipids are based on glycerol backbone.
• Sphingophospholipids are based on the sphingosine backbone.

Glycerophospholipids

• Major phospholipids in membranes.
• Based on a phosphatidic acid backbone.
• Different structural variations create various subgroups.
• Examples include phosphatidylserine, phosphatidylcholine, phosphatidylethanolamine, and cardiolipin.
• Important in cell membranes and mitochondrial function.

Sphingophospholipids

• Sphingomyelin is the primary sphingophospholipid in humans.
• The backbone is sphingosine.
• They are an important component of myelin sheaths in nerve fibers.
• Sphingomyelin degradation plays a crucial role.

Isoprenoids

• Isoprenoids are lipids derived from isoprene.
• Cholesterol is an important example of an isoprenoid.

Cholesterol

• Present in biological membranes.
• Precursor for steroid hormones.
• Has amphipathic character.

Steroids

• All steroids share a common four-ring structure based on cholesterol.
• Examples include sex hormones (estrogen, progesterone, testosterone), and other hormones.

Metabolism of Lipids

• One aspect of lipid metabolism is phospholipid degradation.
• Phospholipases are enzymes that degrade phospholipids. Different types of phospholipases target different phospholipid bonds.

Niemann-Pick Disease

• A rare genetic disorder due to a defective sphingomyelinase enzyme.
• Sphingomyelin accumulates in cells.
• Affects the brain, spleen, and liver.
• Causes mental retardation and early death.
• Distinguished by the presence of foamy cells (accumulation in cells).
• A discussion of the inheritance pattern and the associated accumulation is included.

Tay-Sachs Disease

• Another genetic disorder affecting hexosaminidase A, responsible for degrading a specific ganglioside (GM2).
• This leads to a deficiency in GM2 ganglioside metabolism.
• Associated clinical symptoms.

This quiz explores key concepts in biochemistry related to lipids and hormones, focusing on their structural basis and functions. Questions cover steroid hormones like estrogen and testosterone, Niemann-Pick disease, and the characteristics of fatty acids and lipids in biological membranes.