3.3-Lipids-Part-3

Types of Lipids

  • Two main categories based on biochemical functions:

    • Saponifiable Lipids

    • Non-Saponifiable Lipids

Objectives

At the end of the lesson, students should be able to:

  1. Explain the four major chemical reactions that triglycerides (TAG) undergo.

  2. Identify the general structural characteristics of membrane lipids.

  3. Describe the structure and biochemical function of messenger lipids.

  4. Define and understand protective coating lipids.

Recap of Key Concepts

Fatty Acids

  • Relationship with carbon chain length and degree of unsaturation.

  • Physical properties of fatty acids: melting point and solubility.

Triglycerides (TAG)

  • Most abundant type of lipid in the body.

  • Four chemical reactions that TAGs undergo to form another compound:

    1. Hydrolysis

    2. Saponification

    3. Esterification

    4. Transesterification

  • Saponification steps involve splitting TAGs into glycerol and fatty acids through hydrolysis and ester reactions.

Fat Substitutes

  • Known as "artificial fats"; replicate properties of natural fats without being lipids.

  • Provide sensations of richness and creaminess in foods.

  • Helps reduce negative health impacts associated with dietary fats.

  • Types include:

    • Calorie-reduced fat substitutes

    • Calorie-free fat substitutes

Membrane Lipids

Types of Membrane Lipids

  1. Phospholipids

    • Most abundant type of membrane lipids.

    • Composed of:

      • One or more fatty acids

      • A phosphate group

      • A platform molecule (glycerol or sphingosine).

    • Structure consists of a hydrophilic head and hydrophobic tails.

  2. Sphingolipids

    • Contains fatty acids and sphingosine.

    • Includes:

      • Glycerophospholipids

      • Sphingomyelins

      • Sphingoglycolipids.

Phospholipids Structure

  • Has two fatty acids and a phosphate group esterified to glycerol.

  • Four ester linkages in glycerophospholipids.

  • Undergo hydrolysis and saponification similar to triglycerides, with a complexity due to their additional phosphate group.

Sphingophospholipids

  • Contains:

    • One fatty acid

    • One phosphate group linked to sphingosine.

  • Structure includes a head group (with phosphate) and tails (fatty acid and sphingosine).

  • Participates in hydrolysis and saponification reactions.

Sphingoglycolipids

  • Contains both a fatty acid and a carbohydrate component attached to sphingosine.

  • Structure includes a polar head (monosaccharide) and non-polar tails.

Types of Sphingoglycolipids

  1. Cerebrosides

    • Contain a single monosaccharide; found in the brain.

  2. Gangliosides

    • Contain branched chains of multiple monosaccharides; found in the nervous system.

Cholesterol

  • A non-saponifiable lipid with a steroid structure.

  • Lacks fatty acid residues.

  • Important for cell membranes and a precursor for other steroids.

  • Exists in various tissues, sparingly soluble in water.

  • Transported in the bloodstream via lipoproteins: LDLs (bad cholesterol) and HDLs (good cholesterol).

Emulsification Lipids

  • Substances that can disperse and stabilize water-insoluble substances in aqueous solutions.

  • Key for lipid digestion in conjunction with bile acids.

  • Bile acids are derived from cholesterol, enhancing the absorption of dietary lipids.

Messenger Lipids

  • Lipids that act as signaling molecules between tissues.

  • Main types: steroid hormones (sex hormones, adrenocorticoids) and eicosanoids.

Steroid Hormones

  1. Sex Hormones

    • Estrogens: female hormones.

    • Androgens: male hormones, induce muscle growth.

    • Progestins: regulate uterine lining and suppress ovulation.

  2. Adrenocorticoid Hormones

    • Mineralocorticoids and glucocorticoids regulate ion balance and glucose metabolism.

Eicosanoids

  • Messenger lipids derived from arachidonic acid, influencing various physiological responses.

    • Prostaglandins, thromboxanes, and leukotrienes are major types affecting inflammation, blood pressure, and immune responses.

Protective Coating Lipids

  • Biological waxes, which are monoesters of long-chain fatty acids and long-chain alcohols.

  • Function: provide water-repellent properties, essential for skin, feathers, and plant leaves.

Types of Lipids

  • Categories: Saponifiable Lipids, Non-Saponifiable Lipids

Objectives

Students should be able to:

  • Explain the four major reactions of triglycerides (TAG)

  • Identify characteristics of membrane lipids

  • Describe structure/function of messenger lipids

  • Define protective coating lipids

Key Concepts

  • Fatty Acids: Relationship with carbon chain length and unsaturation; impacts on melting point and solubility.

  • Triglycerides (TAG): Most common lipid type; undergo four reactions: hydrolysis, saponification, esterification, transesterification.

  • Fat Substitutes: Artificial fats providing richness without lipid content; types include calorie-reduced and calorie-free fat substitutes.

Membrane Lipids

  • Types:

    • Phospholipids: Predominant membrane lipids; consist of fatty acids, phosphate, and glycerol/sphingosine. Hydrolysis and saponification similar to TAGs.

    • Sphingolipids: Fatty acids and sphingosine; includes glycerophospholipids, sphingomyelins, spingoglycolipids.

    • Cholesterol: Non-saponifiable lipid, key for membranes and steroid precursor; transported via LDLs (bad) and HDLs (good).

Emulsification Lipids

  • Stabilize water-insoluble substances; crucial for lipid digestion alongside bile acids.

Messenger Lipids

  • Signaling molecules; main types are steroid hormones and eicosanoids (e.g., prostaglandins, leukotrienes).

Protective Coating Lipids

  • Biological waxes providing water-repellent properties, essential for various biological surfaces.