Lecture Notes on Lipids

Introduction to Lipids

• Lipids are the third class of biomolecules discussed.
• Wide variety of functions: oils, fats, cholesterol, vitamins E & K.
• Source of hormones like sex hormones.
• Olive oil contains phenolic compounds which act as antioxidants.

Comparison with Proteins

• Proteins have amino acids folded into 3D structures (enzymes, receptors).
• Lipids have varied structures and functions.
• Defined as molecules insoluble in water but soluble in organic solvents.

Classes of Lipids

1. Free Fatty Acids

   • Common fuel, preferred energy source for some organs.
   • Brain switches between glucose and ketone bodies.
   • Adipose tissues primarily use fatty acids and glucose.
   • Red blood cells mainly use glucose.

2. Triacylglycerols

   • Storage form of fatty acids.

3. Membrane Lipids

   • Phospholipids: Key in membranes.
   • Glycolipids: Carbohydrates conjugated to lipids.
   • Steroids: Polycyclic hydrocarbons with varied functions.

Free Fatty Acids

• Origin from fats/oils; fats solid, oils liquid at room temperature.
• Saturated vs. Unsaturated
  • Saturated: All single bonds.
  • Unsaturated: Presence of cis double bonds.

Nomenclature of Fatty Acids

• Delta Numbering: From carbonyl carbon.
• Omega Numbering: From terminal methyl.
• Example: 18:1 Δ9 vs. 18:1 ω9.

Natural Fatty Acids

• Common lengths: C16 & C18.
• Medium chain triglycerides (MCTs) in oils like coconut.
• Different physiological forms based on pH.
• Importance of cis/trans configuration in physical properties.

Importance of Unsaturated Fatty Acids

• Essential fatty acids: Cannot be synthesized by humans.
• Found in sources like olive oil and fish (e.g., omega-3 fatty acids).

Triacylglycerols

• Storage form with glycerol backbone and esterified fatty acids.
• Found in oils/fats, released as free fatty acids during degradation.

Membrane Lipids

1. Phospholipids: Glycerol or sphingosine platform.
2. Glycolipids: Carbohydrate-lipid conjugates, recognized by toxins.
3. Cholesterol: Maintains membrane fluidity, precursor for steroid hormones & vitamin D3.

Properties of Membrane Lipids

• Amphipathic: Polar head and nonpolar tail.
• Protein-lipid conjugates localize proteins to membrane.

Key Concepts

• Physical properties like melting points influenced by structure.
• Steroids include cholesterol; cholesterol vital for cell membrane fluidity and precursor to other essential molecules.

Conclusion

• Lipids play various roles in biological systems, from energy storage to cell membrane integrity and signaling. Understanding their structure and function is crucial for biochemistry.

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