CHEM 452 Chapter 10 Lecture Outline Filled in PDF

# Chapter 10: Lipids Structure ## Read Chapter 10 ## Properties of Lipids - NONPOLar to very slightly - Highly reduced - Generally insoluble in water. - Soluble in organic solvents (e.g. chloroform and acetone) ## Functions of Lipids 1. energy storage 2. Cell Structure 3. Lipid soluble vitamin...

# Chapter 10: Lipids Structure ## Read Chapter 10 ## Properties of Lipids - NONPOLar to very slightly - Highly reduced - Generally insoluble in water. - Soluble in organic solvents (e.g. chloroform and acetone) ## Functions of Lipids 1. energy storage 2. Cell Structure 3. Lipid soluble vitamins 4. signaling molecules - hormones ## Some lipids are very hydrophobic (NP) - lack polar head group ## Some are amphipathic (polar + NP) - contain polar head group ## Two main groups of lipids 1) open chain compound with a polar head and long chain nonpolar tails like fatty acids or 2) fused ring compound, such as cholesterol and steroids ## 1. Fatty acids ### a. Function: fuel source ### b. General properties - Contain a carboxyl head group (polar) attached to a nonpolar hydrocarbon tail - This makes it an amphipathic molecule, Slightly water soluble - Characteristics: 1) even # of c 2) unbranched 3) saturated (no double bonds) monounsaturated (one double bond) or polyunsaturated (multiple double bonds) - The carboxyl group is polar (ionized at neutral pH) gives fatty acids slight solubility in water ### c. Nomenclature of fatty acids Specify **chainlength** and **# DB** Position of double bond are specified by **subscripts # of followed by Δ** ### Examples: - Palmitic acid (16 carbon saturated fatty acid) 16:0 - Oleic Acid (18 carbon monounsaturated fatty acid, db between C9 and C10) 18:1Δ9 - Linoleic Acid (18 carbon fatty acid polyunsaturated fatty acid, db between C9 and C10, C12 and C13) 18:2Δ9,12 ### d. Number of carbons and double bonds i. Fatty acids have **even #** of carbon atoms (due to the way they are synthesized uses acetyl-CoA) ii. There is a common pattern of location of double bonds - The double bond is typically between _C9 + C10_ (Δ9) for most unsaturated fatty acids - In polyunsaturated fatty acids, additional double bonds are at _C12 + C13_ (Δ12) and _C15 + C16_ (Δ15) - **omega fatty acids**: polyunsaturated fatty acids. "omega" designation refers to the position of the last double bond iii. The length and saturation influences melting point and fluidity - The **longer** the fatty acid chain and the **fewer** DB, **lowering** the melting point and **increasing** the solubility in water. - This is because: - saturated chains will pack more tightly versus unsaturated - Due to more van der Waals and hydrophobic forces - In unsaturated fatty acids the stereochemistry of double are *cis C15*, rather than *trans C15* - This puts a kink in the hydrocarbon tail - This disrupts hydrophobic interactions - hydrogenation -adding hydrogen across double bond of unsaturated fatty acids to produce saturated fats - ex: margarine (partially hydrogenated vegetable) - As a biproduct of the process, *trans fats* (fats with *trans* double bond) are created - *trans fats* can pack more easily than *cis fats* - *trans fats* increases LDL cholesterol, a positive correlator of heart disease ## 2. Triglycerides (Triacylglycerols) ### a. How triglycerides are made Recall how to make an ester: alcohol + carboxyl → ester ### Functions: Fat Storage + insulation ### General properties: - More hydrophobic (compared to free fatty acids) - More reduced than sugars (more energy derived compared to sugar) - Stored as in *lipid droplets* - Not typically in *membranes* in adipose cells, unhydrated - Fatty acyl tails can vary in chain length and saturations ### b. Hydrolysis of triglycerides 1. **Enzymatic** - **Lipases**: adds water across ester bond to release fatty acid - products: 3 fatty acids + glycerol molecule 2. **Chemical - Saponification (making Soap)** - NaOH and KOH hydrolyze bond to make fatty acid salts - products: 1-glycerol molecule + Salt (3Na+ ionized fatty acid ## 3. Membrane Lipids: - Components of membranes (unlike triglycerides that are stored) - Contain phosphate or other charged polar groups - amphipathic molecules (slightly water soluble) ## A. Phosphoglycerides (Phosphoacylglycerol or phospholipids or glycerophospholipid) ### 1. How they are made alcohol + phosphate → phosphoester - A phosphoglyceride is glycerol attached to fatty acid (ester bond) and phosphate (phosphoester bond). - The phosphate group can be attached to an additional group (X) where *x: hydroxyl containing* group attached by phosphoester bond. ### 2. Some example glycerophospholipids i. Phosphatidylcholine - Phosphate is connected to choline group - The most common membrane lipid - Net charge is 0 ii. Phosphatidylserine - Phosphate is connected to serine - Net charge -1 - Common on the inner leaf of the plasma membrane iii. Phosphatidylethanolamine - Phosphate is connected to ethanolamine group - Net charge neutral (0) - Small head group makes this a "cone shaped" lipid (creates negative membrane curvature) v. Phosphatidylinositol - Net charge negative (-1) - Key signaling lipid: The inositol head group can be phosphorylated on multiple different positions. Each form serves a distinct signaling role in the cell. - For example, PIP3 is phosphatidylinositol phosphorylated at positions 3,4,5 and is involving in insulin signaling ## B. Sphingolipids ### Function: - membrane components - Found primarily in central nervous system ### Structure: - Sphingosine backbone (instead of glycerol) - Attached to fatty acid via amide bond - X=head group ### Some example sphingolipids 1. ceramide x= H 2. Sphingomyeline x= phosphocholine group ### Ceramide and Sphingomyelin are membrane components in the central nervous system ### c. Glycolipids - Carbohydrate (sugar) bound to off of lipid by *ether linkage* (no phosphate). - Backbone is usually *ceramide* - Sugar is usually *glucose* or *galactose* - Often found in nerve and brain membranes # Archaeal Lipids - Allow archaeal bacteria to survive in extreme condition ## Steroids Structure: Fused ring system containing 1-5membered ring and 3-16 membered rings Functions: Hormones, membrane components, some vitamins ## Cholesterol - **do not have to be able to draw cholesterol. Be able to recognize structure.** Function: membrane component in animals - **stiffen membranes (reduces fluidity)**