Notes on Lipids: Structure, Fatty Acids, and Classification (Study Notes)

Section 1: Amphipathic Lipids and Membrane Concepts

• Amphipathic lipid

• Lipid bilayer

• Polar head

• Micelle

• Aqueous phase

Section 2: Types of Fatty Acids – Saturated

• General formula: The general formula for these acids is $C<em>nH</em>{2n+1}COOH$.

• Physical state: They tend to be solid at room temperature.

• Bonding: They have single bonds (no double bonds).

• Health implications: They may increase blood cholesterol levels and cardiovascular diseases.

• Classification: They may be divided into two groups:

  1. Straight chain fatty acids: found in plants and animals.

  • Example: Stearic acid- $CH<em>3(CH</em>2)_{16}COOH$

  • Example: Palmitic acid- $CH<em>3(CH</em>2)_{14}COOH$

  1. Branched chain fatty acids: minor component of natural fat or oil.

  • Example: Isopalmitic acid- $(CH<em>3)</em>2CH(CH<em>2)</em>{12}COOH$

  • Found in wool

Section 3: Simple Lipid and Classification of Lipids

• Lipid types:

  • Compound lipid

  • Derived lipid

  • Fat & Oils

  • Wax

  • Phospholipids

  • Lecithin

  • Cephalins

  • Phosphatidyl-

  • Glycolipids

  • Cerebrosides

  • Gangliosides

  • Steroids

  • Terpenoid

  • Monoterpen

  • Diterpenes

  • Inositol

  • Sphingomyelins

Section 4: Fatty Acids – Building Blocks and Chain Lengths

• Fatty acids are building blocks of lipids. They are naturally occurring carboxylic acids with an unbranched carbon chain and an even number of carbon atoms.

• Biosynthesis pathway: Fatty acids almost always contain an even number of carbon atoms when biosynthesized.

• Chain length categories:

  • Long-chain fatty acids: $12 \text{ to } 26$ carbon atoms; found in meats and other sources. $12 \leq \text{C atoms} \leq 26$

  • Medium-chain fatty acids: $6 \text{ to } 10$ carbon atoms;

  • Short-chain fatty acids: fewer than $6$ carbon atoms; occur primarily in dairy products.

• Saturated vs. unsaturated: Fatty acids can be either saturated or unsaturated.

Section 5: Types of Fatty Acids – Unsaturated

• Features: Unsaturated fatty acids contain double bonds in the carbon chain.

• Physical state: Unsaturated fats are liquid at room temperature.

• Health and lifestyle implications: They are generally considered beneficial fats; they can decrease blood cholesterol levels, stabilize heart rhythms, and support various other beneficial roles.

• Examples with double-bond counts and formulas:

  • Oleic acid: $C<em>nH</em>{2n-1}COOH$ (contains one double bond)

  • Linoleic acid: $C<em>nH</em>{2n-3}COOH$ (two double bonds)

  • Linolenic acid: $C<em>nH</em>{2n-5}COOH$ (three double bonds)

  • Arachidonic acid: $C<em>nH</em>{2n-7}COOH$ (four double bonds)

• Notes on notation: The formulas above reflect the general relationship between hydrogen count and degree of unsaturation; each double bond reduces the hydrogen count by 2 relative to the saturated counterpart.

Practical and contextual connections

• Amphipathic properties underpin membrane structure: lipid bilayers form due to hydrophobic tails and hydrophilic heads organizing in aqueous environments.

• Micelles often form when certain lipids (with a single fatty acid tail) aggregate in water, highlighting how molecular shape influences assembly.

• Diet and health implications: Saturated fats are typically solid at room temperature and have been associated with higher cholesterol and cardiovascular risk, whereas unsaturated fats are more fluid, often liquid at room temperature, and linked to favorable lipid profiles.

• Foundational principles: Lipids serve as energy storage (triglycerides), structural components (phospholipids in membranes), and signaling molecules (eicosanoids from arachidonic acid, etc.).

Formulas and symbols used (summary)

• Saturated fatty acid general formula: $C<em>nH</em>{2n+1}COOH$

• Stearic acid: $CH<em>3(CH</em>2)_{16}COOH$

• Palmitic acid: $CH<em>3(CH</em>2)_{14}COOH$

• Isopalmitic acid: $(CH<em>3)</em>2CH(CH<em>2)</em>{12}COOH$

• Oleic acid: $C<em>nH</em>{2n-1}COOH$

• Linoleic acid: $C<em>nH</em>{2n-3}COOH$

• Linolenic acid: $C<em>nH</em>{2n-5}COOH$

• Arachidonic acid: $C<em>nH</em>{2n-7}COOH$

Notes on terminology and typos observed in the source

• Corrected terms for clarity: polarization head group (polar head), aqueous phase, and sphingomyelin (spelling adjusted from Sphingomvelins).

• Some entries in the source list have typographical errors (e.g., Beewax -> Beeswax; Phosphotidyl- -> Phosphatidyl-; Sphingomvelins -> Sphingomyelins). The meaning is preserved in these notes.