Timberlake_Ch15_Notes

Chapter 15: Lipids

Date: 10 November 2025

Review

  • Key topics covered include:
    • Carboxylic acid structure and properties
    • Hydrogenation of C=C double bonds
    • Hydrolysis of esters under acidic and basic conditions

Learning Objectives

  • Classify fatty acids as saturated or unsaturated.
  • Draw line–angle structures for:
    • Waxes
    • Triacylglycerols formed from fatty acids and alcohol or glycerol
  • Predict the products of:
    • Hydrogenation of triacylglycerols
    • Hydrolysis of triacylglycerols
    • Saponification of triacylglycerols

Lipids

  • Definition: Lipids are biomolecules that are insoluble in water but soluble in organic solvents.
  • Fatty Acid: A long carbon chain with a carboxylic acid group.
    • Naming convention: (carbon atoms : double bonds), e.g., lauric acid (12:0)

Fatty Acids

  • Saturated Fatty Acid:
    • Contains only C–C single bonds.
    • Fatty acids “stack” more efficiently, resulting in higher melting points.
  • Monounsaturated Fatty Acid:
    • Contains one C=C double bond.
  • Polyunsaturated Fatty Acid:
    • Contains two or more C=C double bonds.
    • Example:
    • Oleic acid (18:1, cis)
    • Elaidic acid (18:1, trans)

Prostaglandins

  • Definition: Prostaglandins are 20-carbon lipids with hormone-like activity.
  • Synthesis Inhibition: The synthesis of prostaglandins is inhibited by NSAIDs such as acetaminophen and ibuprofen.
  • Examples of Fatty Acids Relevant to Prostaglandins:
    • Linoleic acid (18:2, OH, OH)
    • Arachidonic acid (20:4, HO, OH)
    • Prostaglandin E₁ (HO, OH)
    • Prostaglandin F₂ (OH, CO)

Fatty Acids Practice

  • Group Activity:
    • Classify provided fatty acids as saturated, monounsaturated, or polyunsaturated.
    • Identify double bonds as cis or trans.
    • Use shorthand notation (carbon atoms:double bonds) for naming.

Fatty Acid Esters

  • Wax: An ester derived from a fatty acid and a long-chain alcohol, e.g., beeswax (triacontanyl palmitate).
  • Triacylglycerol: A triester derived from glycerol and three fatty acids.
    • Named using the format “glyceryl” + fatty acid carboxylate name.

Hydrogenation of Fatty Acids

  • Process: Hydrogenation of unsaturated fats produces saturated fats.
  • Partial Hydrogenation: Can produce trans fats.
  • Chemical Reaction Example:
    • From unsaturated to saturated via
    • (extC=C)+H2<br/>ightarrowextC–C( ext{C=C}) + H_2 <br /> ightarrow ext{C–C}

Hydrolysis of Triacylglycerols

  • Mechanism: Follows the same mechanism as the hydrolysis of esters in acidic and basic conditions.
  • Saponification: The hydrolysis of fatty acids in basic conditions, leading to the formation of soap.

Triacylglycerols Practice

  • Group Activity:
    • Predict the products of reacting each triacylglycerol under the following conditions:
    1. H₂, Ni
    2. H₂SO₄, H₂O, heat
    3. KOH, H₂O, heat

Reminders

  • Due Dates:
    • Deal Lab 10 Prelab: 11/12 at 8:00 am
    • Deal Lab 10 Report: 11/14 at 11:59 pm
    • Week 14 Homework: 11/16 at 11:59 pm
    • Week 14 Quiz: 11/16 at 11:59 pm

Chapter 15: Lipids

Date: 12 November 2025

Review

  • Key Topics Covered:
    • Triacylglycerol structure and polarity
    • Amide bond structure

Learning Objectives

  • Draw the structure of a phospholipid containing either:
    • Glycerol
    • Sphingosine
  • Compare and contrast the structures of steroids.
  • Describe common functions of steroids in the body.
  • Describe the composition and function of the lipid bilayer in cell membranes.

Phospholipids

  • Glycerophospholipid:
    • A lipid in which glycerol and an amino alcohol are linked by a phosphate ester.
    • Structure:
    • Hydrophilic head (composed of amino alcohol + phosphate)
    • Hydrophobic tail (composed of fatty acid chains)

Phospholipids

  • Sphingomyelin:
    • A lipid where sphingosine and an amino alcohol are linked by a phosphate ester.
    • This is a large component of the myelin sheath surrounding axons.

Phospholipids Practice

  • Group Activity:
    • Draw the structure of a phospholipid composed of the following units:
    1. Glycerol, 2 stearic acids (18:0), and serine
    2. Glycerol, 2 oleic acids (18:1), and ethanolamine
    3. Sphingosine, palmitic acid (16:0), and choline
    4. Sphingosine, stearic acid (18:0), and ethanolamine

Steroids

  • Definition: Steroids are compounds characterized by a fused ring core structure.
  • Bile Salt:
    • A compound derived from cholesterol that facilitates the breakdown of fats.

Transporting Cholesterol

  • Lipoprotein:
    • An assembly that transports lipids through the bloodstream, consisting of:
    • Polar surface: Composed of phospholipids
    • Inner core of nonpolar lipids: Includes cholesteryl esters and/or triacylglycerols
    • Associated membrane proteins

Transporting Cholesterol

  • Plaque Formation:
    • Cholesterol can accumulate in arteries, leading to plaque formation.
  • Lipid Types:
    • High-Density Lipoproteins (HDLs) contain significantly less cholesterol and more proteins compared to Low-Density Lipoproteins (LDLs), often referred to as “good cholesterol” and “bad cholesterol,” respectively.

Steroid Hormones

  • Definition: Hormones are chemical compounds that trigger signaling pathways.
    • Examples include natural sex hormones and anabolic steroids:
    • Testosterone
    • Estradiol
    • Progesterone
    • Methandienone
    • Oxandrolone
    • Stanozolol

Steroid Hormones

  • Corticosteroid:
    • A steroid produced in