Untitled Quiz

Lipid Structure and Function

• Lipids are organic compounds that are insoluble in aqueous solutions but soluble in organic solvents like ether, chloroform, benzene, and acetone.
• Lipids are classified into three main groups: simple, compound, and derived lipids.

Simple Lipids

• Simple lipids are esters formed from fatty acids and alcohol.
• Fats are esters of fatty acids and glycerol.
• Waxes are esters of fatty acids and alcohols with higher molecular weights.

Compound Lipids

• Compound lipids are formed from simple lipids and other non-lipid components.
• Phospholipids are a type of compound lipid.
• Glycolipids are another type of compound lipid.
• Other complex lipids are also included in this category.

Derived Lipids

• Derived lipids are substances derived from simple and compound lipids through hydrolysis or associated with lipids in nature.
• Examples of derived lipids include fatty acids, alcohols (like glycerol and sphingosine), sterols (like cholesterol), steroids, and fat-soluble vitamins (A, K, E, and D).

Fatty Acids (F.A.)

• Fatty acids are usually straight-chain organic acids containing an even number of carbon atoms.
• Fatty acid chains are numbered either from the carboxylic group or from the methyl (omega) end.

Saturated Fatty Acids (SFA)

• Saturated fatty acids have no double bonds.

• The general formula is CH₃-(CH₂)ₙ-COOH.

• Saturated fatty acids are further classified according to the number of carbon atoms (short-chain, medium-chain, long-chain).

• Examples include Acetic acid (2C), Butyric acid (4C), Palmitic acid (16C), and Stearic acid (18C).

Unsaturated Fatty Acids (USFA)

• Unsaturated fatty acids have one or more double bonds.
• Monounsaturated fatty acids have one double bond (e.g., palmitoleic acid, oleic acid).
• Polyunsaturated fatty acids (PUFA) have more than one double bond, they are also essential fatty acids (EFAs) because they can't be synthesized by the body and must be consumed in the diet (e.g., Linoleic acid, α-Linolenic acid, Arachidonic acid).

1-Linoleic Acid

• C18:2△9,12
• Important because other essential fatty acids can be synthesized from it in the body

2-Alpha-Linolenic Acid

• C18:3△9,12,15;
• Located in corn, peanuts, olives, cottonseed, and soybean oils

3-Arachidonic Acid

• C20:4△5,8,11,14
• Important in animal tissues and peanut oil.
• Precursor of prostaglandins

3-Nervonic Acid

• (Unsaturated lignoceric acid) ω9, C24:1△15
• Found in cerebrosides

Classification of Lipids according to presence or absence of double bonds:

• Saturated Fatty Acids (SFA)
• Unsaturated Fatty Acids (USFA)

Classification of Lipids according to nutritional importance:

• Essential Fatty Acids (EFA)
• Non-essential Fatty Acids (NEFA)

Essential Fatty Acids: EFAs

• Cannot be synthesized in the human body.
• Must be consumed in the diet.
• Precursors of other fatty acids via chain elongation and desaturation.
• Examples: Linoleic acid and α-linolenic acid

Non-Essential Fatty Acids: NEFAs

• Can be synthesized in the human body.

Waxes

• Solid simple lipids.
• Contain a monohydric alcohol with a higher molecular weight than glycerol, esterified to long-chain fatty acids.

Natural Waxes (e.g. Bee Wax)

• Mixture of waxes with mericyl palmitate as the main component.

Other Conjugated Lipids (Compound Lipids)

• Phospholipids
• Glycolipids
• Lipoproteins

1-Phospholipids

• Compound lipids containing phosphoric acid in their structure.
• Composed of fatty acids (saturated and unsaturated), nitrogenous bases (choline, serine, threonine, or ethanolamine), phosphoric acid, and fatty alcohols (glycerol or sphingosine).
• Two main types: Glycerophospholipids and Sphingophospholipids.
• Important component of cell membranes.

Glycerophospholipids

• Phosphatidic acid (PA) - simplest form, composed of diacylglycerol and phosphate on the third carbon.
• Other types exist with diverse head groups (e.g., phosphatidylcholine, phosphatidylethanolamine).

Sphingophospholipids (Sphingomyelins)

• Contain sphingosine instead of glycerol.
• Synthesized from serine and palmitic acid.
• Abundant in brain and nerve tissue.

2-Glycolipids

• Contain carbohydrate residues, sphingosine as the alcohol, and a very long-chain fatty acid (24 carbon series).
• Present in cerebral tissue (called cerebrosides).
• Classified according to the number and nature of the carbohydrate present (e.g. cerebrosides, sulfatides, gangliosides).

3- Lipoproteins

• Compound lipids composed of lipid and protein parts (apolipoproteins).
• Transport lipids in the blood.
• Classified according to their density (HDL, LDL, VLDL).

Triacylglycerol

• Simple lipids, also known as neutral fats.
• Formed from glycerol and three fatty acids.

Importance of Lipids

• Energy source
• Important part of cell membranes
• Insulation
• Building Materials (hormones)
• Providing essential fatty acids (EFAs)
• Component of lipoproteins that transport lipids.