Lipids Cheatsheet

Cheatsheet Content

### Lipids: Definition - **Definition:** A diverse group of organic compounds that are largely nonpolar and hydrophobic, making them insoluble in water but soluble in organic solvents (e.g., ether, chloroform, benzene). - **Key Biological Roles:** - Energy storage (fats and oils) - Structural components of cell membranes (phospholipids, cholesterol) - Signaling molecules (steroid hormones, prostaglandins) - Insulation and protection ### Distinction Between Fats and Oils - Both are types of **triglycerides** (triacylglycerols), composed of a glycerol molecule esterified with three fatty acids. - **Fats:** - Typically **solid** at room temperature. - Rich in **saturated fatty acids**, which have no double bonds in their hydrocarbon chains, allowing them to pack tightly. - Commonly found in animals (e.g., butter, lard). - **Oils:** - Typically **liquid** at room temperature. - Rich in **unsaturated fatty acids**, which contain one or more double bonds (mono- or polyunsaturated) in their hydrocarbon chains. These double bonds introduce kinks, preventing tight packing. - Commonly found in plants (e.g., olive oil, sunflower oil). ### Structure of Lipids: Fatty Acids - **Basic Structure:** Long hydrocarbon chain (typically 4 to 28 carbons) with a terminal carboxyl group ($\text{-COOH}$). - **Types:** - **Saturated Fatty Acids (SFAs):** No carbon-carbon double bonds. - Example: Palmitic acid ($\text{CH}_3(\text{CH}_2)_{14}\text{COOH}$) - **Unsaturated Fatty Acids:** Contain one or more carbon-carbon double bonds. - **Monounsaturated Fatty Acids (MUFAs):** One double bond. - Example: Oleic acid ($\text{CH}_3(\text{CH}_2)_7\text{CH}=\text{CH}(\text{CH}_2)_7\text{COOH}$) - **Polyunsaturated Fatty Acids (PUFAs):** Two or more double bonds. - Example: Linoleic acid ($\text{CH}_3(\text{CH}_2)_4(\text{CH}=\text{CHCH}_2)_2(\text{CH}_2)_6\text{COOH}$) - **Nomenclature:** - **Delta ($\Delta$) numbering:** Indicates the position of double bonds relative to the carboxyl end. E.g., $\text{C18:1}\Delta^9$ (18 carbons, 1 double bond at carbon 9). - **Omega ($\omega$ or n) numbering:** Indicates the position of the first double bond relative to the methyl ($\text{CH}_3$) end. E.g., $\omega\text{-3}$ fatty acid. ### Structure of Lipids: Glycerolipids - **Definition:** Lipids based on a glycerol backbone. - **Glycerol:** A three-carbon alcohol with a hydroxyl group on each carbon. $$\text{CH}_2\text{OH}-\text{CHOH}-\text{CH}_2\text{OH}$$ - **Types:** - **Monoacylglycerols:** One fatty acid attached to glycerol. - **Diacylglycerols:** Two fatty acids attached to glycerol. - **Triacylglycerols (Triglycerides):** Three fatty acids esterified to glycerol. - Primary form of fat storage in animals and plants. - Nonpolar, very hydrophobic. $$\text{CH}_2\text{OOCR}_1$$ $$\text{CHOOCR}_2$$ $$\text{CH}_2\text{OOCR}_3$$ - **Phospholipids (Glycerophospholipids):** A glycerol backbone with two fatty acids and a phosphate group attached (often with an additional head group like choline, ethanolamine, serine, or inositol). - Amphipathic: Have a hydrophilic (polar) head and hydrophobic (nonpolar) tails. - Major components of cell membranes, forming lipid bilayers. $$\text{CH}_2\text{OOCR}_1$$ $$\text{CHOOCR}_2$$ $$\text{CH}_2\text{OPO}_3\text{X}$$ (where X is the head group) ### Structure of Lipids: Sphingolipids - **Definition:** Lipids based on a sphingosine backbone, rather than glycerol. - **Sphingosine:** An amino alcohol with a long unsaturated hydrocarbon chain. $$\text{CH}_3(\text{CH}_2)_{12}\text{CH}=\text{CH}-\text{CH}(\text{OH})-\text{CH}(\text{NH}_2)-\text{CH}_2\text{OH}$$ - **Types:** - **Ceramide:** Sphingosine with a fatty acid attached via an amide linkage to the amino group. - **Sphingomyelins:** Ceramides with a phosphocholine or phosphoethanolamine head group. - Major components of myelin sheath in nerve cells. - **Glycosphingolipids:** Ceramides with one or more sugar residues attached to the primary hydroxyl group (no phosphate). - **Cerebrosides:** One sugar (glucose or galactose). - **Gangliosides:** Oligosaccharide chain with at least one sialic acid. - Found on the outer surface of cell membranes, involved in cell recognition and signaling.