Lipid Chemistry Review

Flashcards covering lipid definitions, classification (simple, complex, derived), fatty acid properties, biological functions, and chemical tests for purity.

How are lipids defined based on their solubility?

Organic substances that are relatively insoluble in water but soluble in organic solvents like chloroform, ether, and benzene.

What are the three main classifications of lipids?

Simple lipids, Complex lipids, and Derived lipids.

How are Simple lipids defined and subclassified?

They are esters of fatty acids with various alcohols; they are subclassified as Neutral fats or oils (alcohol is GLYCEROL) or Waxes (alcohol is other than glycerol).

What is the chemical composition of a Triacylglycerol (Fat)?

It consists of a glycerol backbone esterified with three fatty acids (Acyl residues).

What are Waxes and what are some specific examples?

Esters of fatty acids with higher molecular weight monohydric alcohols; examples include Lanolin, Beeswax, and Whale sperm oil.

What defines a Complex lipid?

Esters of fatty acids with alcohol containing additional prosthetic groups.

What are the components of a Phospholipid?

Fatty acid + alcohol + phosphoric acid, frequently containing nitrogen-containing bases.

How are Phospholipids classified based on the type of alcohol present?

Glycerophospholipids (where the alcohol is Glycerol) and Sphingophospholipids (where the alcohol is Sphingosine).

Provide examples of Glycerophospholipids.

Phosphatidylcholine (Lecithin), Phosphatidyl ethanolamine (Cephalin), Phosphatidyl serine, Phosphatidyl inositol, Plasmalogens, and Cardiolipins.

What is an example of a Sphingophospholipid?

Sphingomyelin.

What are the components of a Glycolipid and name two examples?

Fatty acid + alcohol (Sphingosine) + carbohydrate with a nitrogen base (no phosphate); examples include Cerebrosides and Gangliosides.

Define Lipoproteins and list their types.

Lipids associated with a protein prosthetic group; includes Chylomicrons, Very low density lipoprotein (VLDL), Low density lipoprotein (LDL), and High density lipoprotein (HDL).

What are Derived lipids?

Derivatives obtained on the hydrolysis of group 1 (simple) and group 2 (complex) lipids which possess lipid characteristics.

What are the characteristics of naturally occurring Fatty acids?

They are carboxylic acids with an unbranched carbon chain and almost always contain an even number of carbon atoms.

Classify fatty acid chain lengths by the number of carbon atoms.

Long-chain ($12$ to $26$ carbons), medium-chain ($6$ to $10$ carbons), and short-chain (fewer than $6$ carbons).

What is the difference between saturated and unsaturated fatty acids?

Saturated fatty acids contain only carbon-carbon single bonds (e.g., Palmitic acid), while unsaturated fatty acids contain one or more double bonds (e.g., Oleic acid).

According to the transcript, which two fatty acids are considered 'Essential' and why?

$\alpha$-linolenic acid (omega-3) and Linoleic acid (omega-6); they are essential because the body cannot manufacture them and they must be obtained through the diet.

What are the biological functions of Phospholipids?

They form structural components of membranes, regulate permeability, participate in fat absorption, assist in lipoprotein synthesis, serve as lipotropic factors to prevent fatty liver, and act as precursors for eicosanoids.

What is the significance of Cephalins and Phosphatidyl inositol?

Cephalins participate in blood clotting, and Phosphatidyl inositol is involved in signal transmission across membranes.

Define Rancidity and differentiate between its two types.

Rancidity is the deterioration of fats and oils resulting in an unpleasant taste. Hydrolytic rancidity is caused by bacterial enzyme hydrolysis, while Oxidative rancidity is due to the oxidation of unsaturated fatty acids.

What does the Acid number measure?

The number of milligrams of potassium hydroxide ($KOH$) required to completely neutralize the free fatty acids present in $1\,g$ of fat or oil.

What is the Saponification number and what does it indicate?

The number of milligrams of $KOH$ required to hydrolyze $1\,g$ of fat or oil; it measures the average molecular size of the fatty acids present.

Define the Iodine number and its clinical utility.

The grams of iodine absorbed by $100\,g$ of fat or oil; it determines the degree of unsaturation and helps identify adulteration.

What is the Reichert-Meissl (RM) number and why is it useful for testing butter?

The volume in $ml$ of $0.1\,N\,KOH$ required to neutralize soluble volatile fatty acids from $5\,g$ of fat; it is useful because butter has a high RM number ($25-30$) compared to other edible oils ($<1$).

What is Saponification and what are its products?

The base-catalyzed hydrolysis of an ester; it produces an alcohol and an ionized salt known as soap.