Biochemistry: Lipids and Lipid Metabolism

Comprehensive flashcards covering lipid classification, fatty acid structures, complex lipids, cholesterol properties, and the energetics of beta-oxidation.

Lipids

A heterogeneous group of compounds which are directly or potentially related to fatty acids, primarily non-polar, hydrophobic, and soluble in organic solvents.

Fatty acid

A long or short chain organic acid containing a primary $\text{COOH}$ group and a terminal $\text{CH}_3$ group.

Saturated fatty acids

Hydrocarbon chains that contain no double bonds in their structure and are typically solid at room temperature.

Unsaturated fatty acids

Hydrocarbon chains that have one or more carbon–carbon double bonds ($\text{C=C}$ bonds) and are typically liquids at room temperature.

Monounsaturated fatty acids

Unsaturated fatty acids that contain exactly one $\text{C=C}$ double bond.

Polyunsaturated fatty acids

Unsaturated fatty acids that contain more than one $\text{C=C}$ double bond.

Cis Fatty Acids

Fatty acids where the hydrogen atoms are on the same side of the double bond, resulting in a bent structure.

Trans fatty acids

Fatty acids where the hydrogen atoms are on the opposite side of the double bond, resulting in a straight structure.

Short-Chain Fatty Acids (SCFAs)

Fatty acids with less than $6$ carbon atoms, such as acetic acid ($2\text{C}$) found in vinegar.

Medium-Chain Fatty Acids (MCFAs)

Fatty acids with $6$ to $12$ carbon atoms, such as caprylic acid ($8\text{C}$) found in coconut oil.

Long-Chain Fatty Acids (LCFAs)

Fatty acids with more than $12$ carbon atoms, such as palmitic acid ($16\text{C}$).

Very Long-Chain Fatty Acids (VLCFAs)

Fatty acids with more than $22$ carbon atoms, such as lignoceric acid ($24\text{C}$).

Essential fatty acids

Polyunsaturated fatty acids including linoleate, $\alpha\text{-linolenate}$, and arachidonate which must be obtained from diet because humans lack the enzymes to synthesize them.

Hydrogenation

A commercial process that heats oils in the presence of hydrogen gas to reduce $\text{C=C}$ bonds, converting unsaturated fatty acids into saturated fatty acids.

Triacylglycerols (Triglycerides)

Neutral lipids composed of $1$ molecule of glycerol esterified with $3$ molecules of fatty acids, serving as the primary form of energy storage.

Simple triglycerides

Triglycerides in which all three fatty acids attached to the glycerol molecule are the same.

Mixed triglycerides

Triglycerides in which the attached fatty acids are different, making up $98\%$ of the diet.

Adipocytes

Specific fat cells in animals where triglycerides are stored.

Saponification

The process of making soaps through the hydrolysis of fat in the presence of an alkali such as sodium hydroxide ($NaOH$) or potassium hydroxide ($KOH$).

Glycerophospholipids

Complex lipids made of two fatty acids and one phosphate group attached to a glycerol molecule, commonly found in cell membranes.

Sphingolipids

Compound lipids made of sphingosine (an unsaturated amino alcohol) and a fatty acid, notably lacking glycerol.

Sphingomyelin

A sphingophospholipid that is an important component of the myelin sheath in nerves.

Cerebrosides

Sphingo-glycolipids containing a monosaccharide that are associated with the normal functioning of the central nervous system.

Gangliosides

Sphingo-glycolipids containing a polysaccharide that play an important role in membrane transport mechanisms.

Cholesterol

A derived lipid with the molecular formula $\text{C}_{27}\text{H}_{45}\text{OH}$ and a ring system known as cyclopentano-perhydro phenanthrene (CPP).

LDL cholesterol

Formed by the reaction of cholesterol with saturated fatty acids; considered 'bad' for the heart.

HDL cholesterol

Formed by the reaction of cholesterol with unsaturated fatty acids; considered 'good' for the heart.

Beta ($\beta$) Oxidation

The mitochondrial degradation of long-chain fatty acids into two-carbon units (Acetyl-CoA), starting at the beta carbon.

Carnitine

A carrier molecule that transports fatty-acyl CoA from the cytosol into the mitochondria for degradation.

Activation of fatty acids

The initial step of beta oxidation occurring in the cytosol where fatty acids are converted to fatty acyl CoA, utilizing $2$ ATP.

Energetics of Palmitic acid (16C) degradation

The breakdown of a $16\text{C}$ fatty acid yields a net of $106$ ATP ($80$ ATP from $8$ Acetyl-CoA, $28$ ATP from $7$ cycles, minus $2$ ATP for activation).