Lipids 2

BIOCHEMISTRY - CHEM 2713

Introduction

• Instructor: Dr. Amitabh Jha

• Institution: Acadia University

Lipids Classification

Lipids can be subdivided into the following classes:

1. Fatty acids

2. Triacylglycerols

3. Wax esters

4. Other Fatty Acids: Ecosanoids, etc.

5. Phospholipids

6. Sphingolipids

7. Isoprenoids

8. Lipoproteins

Wax Esters

• Waxes are complex mixtures of non-polar lipids.

• Serve as protective coatings on:
    - Leaves
    - Stems
    - Fruits of plants
    - Skin and fur of animals

• Wax esters consist of long-chain fatty acids and long-chain alcohols.

• Prominent examples include:
    - Carnauba (melissyl cerotate)
    - Beeswax

Examples of Natural Waxes

• Beeswax

• Lanolin

• Spermaceti (animal origin)

• Carnauba wax (vegetal origin)

• Synthetic long-chain aliphatic hydrocarbons like paraffins

Properties of Wax Esters

• Esters formed from long-chain saturated fatty acids and saturated/unsaturated long-chain alcohols.

• Insoluble in water and possess high melting points.

• Functionality includes:
    - Waterproofing feathers in birds
    - Protection from evaporation in tropical plants and ivy
    - Storage of metabolic fuel in plankton
    - Commonly used in lotions, ointments, and polishes.

Other Fatty Acids

• Plants and bacteria can synthesize all required fatty acids from acetyl-CoA.

• Animals primarily acquire fatty acids from dietary sources.

• Distinction between essential and nonessential fatty acids:
    - Nonessential fatty acids: can be synthesized by the body.
    - Essential fatty acids: must be ingested through diet.

• Omega-3 fatty acids:
    - Including alpha-linolenic acid and its derivatives may promote cardiovascular health.

• Certain fatty acids attach to proteins, producing acylated proteins that facilitate environmental interactions.

• Notable modifications:
    - Myristoylation
    - Palmitoylation

Eicosanoids

Eicosanoids are a group of powerful, hormone-like molecules produced in mammalian tissues and include:

• Prostaglandins

• Thromboxanes

• Leukotrienes

• Common precursor: Arachidonic acid, which is linked to various physiological processes:
    - smooth muscle contraction
    - inflammation
    - pain perception
    - blood flow regulation

Prostaglandins

• Prostaglandins contain a cyclopentane ring with hydroxyl groups at C-11 and C-15.

• Functions:
    - Inflammation
    - Digestion
    - Reproduction

Thromboxanes

• Unique for their cyclic ether structure.

• Synthesized by polymorphonuclear lymphocytes.

• Role in platelet aggregation and vasoconstriction after tissue injury.

Leukotrienes

• Named from their discovery in white blood cells, contain a triene group.

• Involvement in:
    - Anaphylaxis
    - Blood vessel fluid leakage
    - White blood cell chemoattraction
    - Vasoconstriction
    - Edema
    - Bronchoconstriction

Aspirin and Eicosanoid Synthesis

• Aspirin inhibits the enzyme PGH2 synthase, which disrupts normal eicosanoid synthesis from arachidonic acid, reducing inflammation by blocking formation of inflammatory mediators.

• A structural representation shows how aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase (Cox).

Membrane Lipids

• Membrane lipids form the double-layered surface of all cells (lipid bilayer).

• Major classes of membrane lipids:
    1. Phospholipids
    2. Glycolipids
    3. Cholesterol

• Membrane lipids are amphiphilic:
    - One end is soluble in water (polar), and the other end is soluble in fat (nonpolar).

Biological Membrane Structure

• Biological membranes consist of polar head groups and two hydrocarbon tails, forming structured shapes like micelles and bilayers.

Phospholipids

• Amphipathic molecules with:
    - Polar head group (phosphate and other polar/charged groups)
    - Hydrophobic fatty acid tails

• Functions include:
    - Membrane formation
    - Emulsification
    - Acting as surfactants

Classification of Phospholipids

1. Lipids that contain phosphate

2. Lipids that do not contain phosphate
      - Further separated into glycerol-based and sphingosine-based.

Types of Phospholipids

• Two main types:

1. Phosphoglycerides

2. Sphingomyelins

• Sphingomyelins:
    - Contain sphingosine instead of glycerol (classified also as sphingolipids).

• Phosphoglycerides:
    - Composed of glycerol, fatty acids, phosphate, and an alcohol.
    - Example: Phosphatidic acid consists of glycerol-3-phosphate and two fatty acids.

• Example phospholipid: Phosphatidylcholine (lecithin) - alcohol esterified to phosphate group as choline.

Table of Major Classes of Phosphoglycerides

Glycosphingolipids

• Third major class of membrane lipids, consisting of sphingolipids attached to carbohydrates.

• Examples include:
    - Cerebrosides: Monosaccharide attached for the head group.
    - Galactocerebroside: Found in brain cell membranes.
    - Gangliosides: Possess oligosaccharide groups; important for nerve function.

Sphingolipid Storage Diseases

• Several lysosomal storage diseases are related to sphingolipid metabolism, termed sphingolipidoses.

• Common diseases include:
    - Tay-Sachs disease:
      - Caused by deficiency of β-hexosaminidase A (enzyme for ganglioside GM2 degradation).
      - Symptoms: blindness, weakness, seizures, mental retardation, death by age three.

Selected Sphingolipid Storage Diseases

Conclusion

 - A comprehensive understanding of lipid classifications, functions, and diseases associated with sphingolipids is crucial for biochemistry studies.

Questions?

• Open floor for student questions regarding the material discussed.