BIOCHEMISTRY: Lipids

Lipids

are a diverse group of organic compounds that are insoluble in water (hydrophobic) but soluble in non-polar organic solvents such as ether, chloroform, benzene, and acetone.

Lipids

are organic compounds composed primarily of carbon (C), hydrogen (H), and oxygen (O), with some containing phosphorus (P), nitrogen (N), and sulfur (S).

Lipids

They are characterized by their poor solubility in water and their important biological functions in energy metabolism, cellular structure, signaling, and insulation.

Characterisitics chemical composition of lipids

• Insoluble in water (hydrophobic)

• Soluble in organic solvents

• Richest source of stored energy

• Provide 9 kcal per gram

• Stored mainly in adipose tissue

• Essential for cell membrane structure

• Necessary for absorption of fat-soluble vitamins (A, D, E, K)

• Protect organs and conserve body heat

Most lipids consist of:

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

Some complex lipids also contain:

• Phosphorus

• Nitrogen

• Sulfur

Types of Lipids

• Fatty Acids

• Triglycerides & Waxes

• Membrane Lipids

• Lipoproteins

• Eicosanoids & Messengers

Fatty Acids

basic building blocks

Triglycerides & Waxes

energy storage + protection

Membrane Lipids

form cell membranes

Lipoproteins

transport lipids in blood

Eicosanoids & Messengers

signaling molecules

Fatty Acids

The structure consists of a hydrocarbon chain with a long tail and a carboxyl group (–COOH head).

Fatty Acids Structure

CH3 −(CH2 )n −COOH

CH₃ =

Methyl (omega) end

(CH₂)ₙ =

Hydrocarbon chain

COOH =

Carboxyl (acid) group

The molecule has two distinct ends:

• Hydrophilic (water-attracting) head

• Hydrophobic (water-repelling) tail

Hydrophilic (water-attracting) head:

Carboxyl group (-COOH)

Hydrophobic (water-repelling) tail:

Hydrocarbon chain

fatty acids are amphipathic molecules.

Because they contain both hydrophilic and hydrophobic regions.

CLASSIFICATION OF FATTY ACIDS:

• Saturated

• Unsaturated

Saturated

Contain only single carbon-carbon (C–C) bonds.

Saturated: Common sources

• Butter

• Cheese

• Coconut oil

• Palm oil

• Animal fat

Unsaturated

• Monounsaturated

• Polyunsaturated

Monounsaturated

• One double bond.

• Usually liquid at room temperature.

Monounsaturated: Example

• Oleic acid (C18:1)

Monounsaturated: Sources

• Olive oil

• Avocados

• Peanuts

• Almonds

Polyunsaturated

• Two or more double bonds.

Polyunsaturated: Examples

• Linoleic acid (Omega-6)

• Alpha-linolenic acid (Omega-3)

• EPA DHA

Polyunsaturated: Sources

• Fish

• Flaxseed

• Walnuts

• Sunflower oil

Triglycerides

also called triacylglycerols or TAGs

Triglycerides

are the most abundant type of lipid (fat) in the human body and in the diet.

Triglycerides

They are the body's primary form of energy storage, accounting for about 95% of dietary fats and most of the fat stored in adipose (fat) tissue.

A triglyceride is composed of:

• 1 glycerol molecule (a three-carbon alcohol)

• 3 fatty acid molecules attached to the glycerol through ester bonds

FUNCTIONS OF TRIGLYCERIDES:

• Primary Energy Reserve

• Thermal Insulation

• Protection of Organs

• Transport of Fat-Soluble Vitamins

• Source of Essential Fatty Acids

Primary Energy Reserve

• Store excess calories for future use.

• Provide 9 kcal per gram, making them the most energy-dense macronutrient.

Thermal Insulation

Help maintain body temperature by reducing heat loss.

Protection of Organs

Cushion and protect vital organs such as the kidneys and heart from physical injury.

Transport of Fat-Soluble Vitamins

Assist in the absorption and transport of vitamins A, D, E, and K.

Source of Essential Fatty Acids

Supply essential fatty acids needed for normal growth, cell function, and hormone production.

TRIGLYCERIDES: Animal Sources

• Butter

• Cheese

• Whole milk

• Fatty meat

• Lard

TRIGLYCERIDES: Plant Sources

• Olive oil

• Coconut oil

• Palm oil

• Avocados

• Nuts and seeds

TRIGLYCERIDES: Processed Sources

• Cakes

• Cookies

• Fried foods

• Fast food Chips

Phospholipids

are a class of complex lipids that are the major structural components of cell membranes.

Phospholipids

are mainly responsible for forming the phospholipid bilayer that surrounds cells and organelles.

Phospholipids

are amphipathic molecules

Phospholipids are amphipathic molecules, meaning they have:

• Hydrophilic ("water-loving") head Contains the phosphate group

• Attracted to water Hydrophobic ("water-fearing") tails Composed of fatty acids

• Repel water

Amphipathic Nature

This unique property allows phospholipids to spontaneously arrange into a bilayer in aqueous environments.

TYPES OF PHOSPHOLIPIDS

• Phosphatidylcholine (Lecithin)

• Phosphatidylethanolamine

• Phosphatidylserine

• Phosphatidylinositol

• Sphingomyelin

Phosphatidylcholine (Lecithin)

• Most abundant phospholipid

• Major component of cell membranes

• Found in egg yolk and soybeans

Phosphatidylethanolamine

• Common in nerve tissue

• Supports membrane flexibility

Phosphatidylserine

• Important in brain function

• Plays a role in cell signaling and apoptosis

Phosphatidylinositol

Involved in intracellular signaling pathways

Sphingomyelin

• Found in nerve cell membranes

• Major component of the myelin sheath

FUNCTIONS OF PHOSPHOLIPIDS

• Form Cell Membranes

• Maintain Membrane Fluidity

• Selective Permeability

• Cell Signaling

• Lipid Transport

• Lung Function

Form Cell Membranes

Principal structural component of plasma membranes and organelle membranes.

Maintain Membrane Fluidity

Help membranes remain flexible while maintaining integrity.

Selective Permeability

Regulate the movement of nutrients, ions, and waste products.

Cell Signaling

Participate in hormone signaling and intracellular communication.

Lipid Transport

Essential components of lipoproteins (HDL, LDL, VLDL), which transport lipids through the bloodstream.

Lung Function

Dipalmitoylphosphatidylcholine is the major phospholipid in pulmonary surfactant, reducing surface tension and preventing alveolar collapse.