Fatty Acids + Lipids + Phospholipids

Structure and Function of Lipids

• Course: BIO00004C Molecular Biology and Biochemistry

• Lecture: 8

• Week: 6

• Instructor: Dr. Patrick Murphy (patrick.murphy@york.ac.uk)

Learning Outcomes

• By the end of the lecture, students should be able to:

  • Describe basic structural features of:

    • Fatty acids

    • Phospholipids

    • Glycolipids

    • Cholesterol

  • Explain chemical properties of:

    • Membrane lipids

    • Neutral lipids

  • Describe structure and dynamics of biological membranes

  • Explain lipid self-assembly to form membranes

Fatty Acids

• Common examples:

  • Saturated: C16:0 (16 carbons, no double bonds)

  • Unsaturated: C18:1 (1 double bond, D9, w-9)

• Double-bond structures can position as:

  • Cis (C cis H R1 R2 C C trans R1 H H R2)

Examples of Fatty Acids

• C18:0: Stearic Acid

• C18:1: Oleic Acid (cis C18:1 D9)

• C18:2: Linoleic Acid (D9,12, cis 9 12)

• C18:3: Linolenic Acid (D9,12,15, cis 9,12,15, w-3, w-6)

Esterification and Hydrolysis

• Esterification process:

  • Glycerol (3 carbons) + 3 Fatty acids = Triglyceride

  • Hydrolysis produces: Glycerol + Fatty Acids + Water

• Lipid structure influences their properties

Neutral Lipids

• Types:

  • Triglyceride: 3 fatty acids

  • Diglyceride: 2 fatty acids

  • Monoglyceride: 1 fatty acid

  • Note: Neutral lipids lack amphipathic properties

Membrane Lipids

• Three common types:

  1. Phospholipids

     • Structure: Fatty acid + Phosphate + Alcohol

  2. Glycolipids

     • Structure: Fatty acid + Phosphate + Sugar

  3. Cholesterol

• Amphipathic nature is crucial for membrane formation

Common Phosphoglycerides

• Examples and structures of:

  • Phosphatidylserine (PS)

  • Phosphatidylcholine (PC)

  • Phosphatidylethanolamine (PE)

  • Diphosphatidylglycerol (Cardiolipin)

Lipids and Membranes

• Key properties of biological membranes:

  • Define inside and outside of the cell

  • Selectively permeable to small molecules

  • Dynamic, fluid structures

  • Composed of lipids and proteins

Eukaryotic Cells and Internal Membranes

• Structures include:

  • Nucleus

  • Mitochondria

  • Endoplasmic reticulum

  • Golgi apparatus

  • Plasma membrane, etc.

Chemical Composition of Membranes

• Percent composition by weight in different membrane types:

  • Myelin: Protein 18%, Lipid 79%, Carbohydrate 3%

  • Plasma membrane (human erythrocyte): Protein 49%, Lipid 43%, Carbohydrate 8%

  • Mitochondrial inner membrane: Protein 76%, Lipid 24%, Carbohydrate 0%

Common Features of Membranes

• Sheet-like structures composed of:

  • Lipids (hydrophobic tails and hydrophilic head groups)

  • Proteins

  • Asymmetric and fluid structures (fluid mosaic model)

• Membranes are non-covalent and dynamically held together by many interactions

Phase Transitions in Lipid Bilayers

• Factors affecting consistency of lipid bilayers:

  1. Temperature: Increased temp leads to fluid-like consistency

  2. Fatty Acid Chain Length: Shorter chains increase fluidity

  3. Fatty Acid Saturation: More unsaturation enhances fluidity

  4. Cholesterol Content: Cholesterol helps maintain membrane integrity

Organisation of Phospholipids

• Asymmetry in membrane bilayers:

  • Flip-flop of phospholipids occurs slowly; they maintain distinct inner and outer leaflets

Summary

• Covered topics include:

  • Structural features of fatty acids, phospholipids, glycolipids, and cholesterol

  • Chemical properties of membrane and neutral lipids

  • Structure and dynamics of biological membranes

  • Mechanism of lipid self-assembly into membranes

Additional Resources

• Past exam paper and specimen answers

• Revision notes on Carbohydrates and Lipids

• MCQs on Mentimeter

Course Overview

• Blocks include:

  1. Nucleic Acids, Gene Expression, and Recombinant DNA technology

  2. Proteins, Carbohydrates, and Lipids

  3. Enzymes

  4. Metabolism

  • Assessment includes exams and practical workshops