πŸ§ͺ Topic 5: Detailed Solutions

Lipids (Π›ΠΈΠΏΠΈΠ΄Ρ‹)
Problem 1: Glycerophospholipid Structure and Nomenclature
πŸ“‹ Task:

The red blood cell membrane contains glycerophospholipid, which consists of glycerol, palmitic acid, oleic acid, phosphoric acid and ethanolamine. Draw the structure of this lipid and name it according to the IUPAC system.

Structure Assembly from Components
Components:
  • Glycerol backbone: 3-carbon chain with hydroxyl groups
  • Palmitic acid: C16:0 (saturated) at sn-1 position
  • Oleic acid: C18:1 Δ⁹ (monounsaturated) at sn-2 position
  • Phosphate + Ethanolamine: Polar head group at sn-3

πŸ“¦ Individual Components:

Glycerol Backbone
sn-1, sn-2, sn-3 positions
Palmitic Acid (16:0)
Saturated fatty acid
Oleic Acid (18:1)
Monounsaturated (Δ⁹)
Phosphoethanolamine
Polar head group
Assembly: Glycerol + 2 Fatty Acids + Phosphate + Ethanolamine
⬇
Phosphatidylethanolamine

🧬 Complete Structure:

1-Palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE)
sn-1: Palmitoyl (C16:0) | sn-2: Oleoyl (C18:1) | sn-3: Phosphoethanolamine

IUPAC Nomenclature:

  1. Backbone: sn-glycerol-3-phosphate
  2. Fatty acids:
    • sn-1: hexadecanoic acid (palmitic, 16:0)
    • sn-2: (9Z)-octadec-9-enoic acid (oleic, 18:1)
  3. Head group: ethanolamine
  4. Full name: 1-hexadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phosphoethanolamine
IUPAC Name: 1-hexadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phosphoethanolamine
Common Name: 1-Palmitoyl-2-oleoyl-phosphatidylethanolamine
Abbreviation: POPE or PE(16:0/18:1)
Class: Glycerophospholipid
Biological Importance:
  • RBC membranes: Major phospholipid component
  • Membrane curvature: Cone-shaped structure
  • Membrane fusion: Important for vesicle fusion
  • Abundance: Second most abundant after phosphatidylcholine
Problem 2: Sphingomyelin Structure
πŸ“‹ Task:

Damage of the myelin sheath of neurons in the central nervous system leads to the development of multiple sclerosis. Draw the structure of sphingomyelin, consisting of sphingosine, oleic acid, phosphoric acid and choline.

Sphingomyelin Structure from Components
Components:
  • Sphingosine: Long-chain amino alcohol (18C backbone)
  • Oleic acid: C18:1 attached via amide bond (not ester!)
  • Phosphocholine: Head group

πŸ“¦ Individual Components:

Sphingosine Backbone
Amino alcohol with trans double bond
Oleic Acid
Forms amide bond with NHβ‚‚
Phosphocholine
Polar head group
Sphingosine + Oleic Acid β†’ Ceramide
⬇
Ceramide + Phosphocholine β†’ Sphingomyelin

🧬 Complete Structure:

N-Oleoyl-Sphingomyelin
Ceramide: Sphingosine + Oleic acid (amide) | Head: Phosphocholine

Key Features:

  1. Sphingosine: (2S,3R,4E)-2-aminooctadec-4-ene-1,3-diol
  2. Ceramide: Sphingosine + fatty acid (amide bond at C2)
  3. Phosphocholine: Attached to C1 hydroxyl
  4. Amide vs Ester: Sphingolipids have amide bond (more stable)
IUPAC Name: N-[(9Z)-octadec-9-enoyl]-(2S,3R,4E)-2-amino-3-hydroxyoctadec-4-enyl phosphocholine
Common Name: N-Oleoyl-sphingomyelin
Class: Sphingolipid (phosphosphingolipid)
Multiple Sclerosis Connection:
  • Myelin sheath: 25% sphingomyelin
  • Demyelination: Loss of sphingomyelin in MS
  • Nerve conduction: Impaired without myelin
  • Lipid rafts: Forms membrane microdomains with cholesterol
Problem 3: Cerebroside Structure
πŸ“‹ Task:

Cerebrosides are found in the brain and in the myelin sheath of nerve tissue. Draw the structure of the cerebroside made of sphingosine, arachidic acid and Ξ²-D-glucopyranose.

Cerebroside (Glucosylceramide) Structure
Components:
  • Sphingosine: Long-chain amino alcohol
  • Arachidic acid: C20:0 (saturated, 20 carbons)
  • Ξ²-D-Glucose: Sugar head group (simplest glycolipid)

πŸ“¦ Individual Components:

Sphingosine
Backbone
Arachidic Acid (20:0)
Very long-chain saturated FA
Ξ²-D-Glucopyranose
Sugar head group
Sphingosine + Arachidic Acid β†’ Ceramide
⬇
Ceramide + Glucose (Ξ²-glycosidic) β†’ Glucosylceramide

🧬 Complete Structure:

N-Arachidoyl-Glucosylceramide
Ceramide: Sphingosine + Arachidic acid | Sugar: Ξ²-D-Glucose (Ξ²1β†’1 linkage)

Structure Features:

  1. Ceramide core: Sphingosine + arachidic acid (amide)
  2. Glycosidic bond: Ξ²-configuration at C1 of glucose
  3. Arachidic acid: Icosanoic acid (20:0, saturated)
  4. Simplest glycosphingolipid: One sugar unit
IUPAC Name: N-icosanoyl-(2S,3R,4E)-2-amino-3-hydroxyoctadec-4-enyl Ξ²-D-glucopyranoside
Common Name: Glucosylceramide or Glucocerebroside
Specific: N-Arachidoyl-glucosylceramide
Class: Glycosphingolipid (neutral)
Biological Importance:
  • Brain tissue: Abundant in gray matter
  • Myelin: Component of nerve sheath
  • Gaucher disease: Deficiency in glucocerebrosidase
  • Cell recognition: Blood group antigens precursor
Problem 4: Testosterone Structure
πŸ“‹ Task:

Testosterone is a male sex hormone. Draw the structure with: a) keto-group at C3, b) double bond C4-C5, c) methyl groups at C10 and C13, d) hydroxyl at C17.

Testosterone Structure
Testosterone
C3: Keto | Δ⁴: Double bond | C17: Ξ²-OH
IUPAC Name: (8R,9S,10R,13S,14S,17S)-17-hydroxy-10,13-dimethyl-1,2,6,7,8,9,11,12,14,15,16,17-dodecahydro-3H-cyclopenta[a]phenanthren-3-one
Systematic: 17Ξ²-hydroxyandrost-4-en-3-one
Class: Androgen (C19 steroid)
Functions: Male sexual characteristics, anabolic effects, protein synthesis, bone density, erythropoiesis
Problem 5: Triacylglycerol Hydrolysis
πŸ“‹ Task:

Write the acid hydrolysis reaction of 1-stearoyl-2-palmitoyl-3-arachinoylglycerol.

Lipolysis Reaction
Reaction:
1-Stearoyl-2-palmitoyl-3-arachinoylglycerol + 3Hβ‚‚O β†’
Glycerol + Stearic acid (C18:0) + Palmitic acid (C16:0) + Arachidic acid (C20:0)
TAG
Glycerol
Reaction type: Acid-catalyzed ester hydrolysis
Products: Glycerol + 3 free fatty acids
Problem 6: Cholesteryl Oleate Formation
πŸ“‹ Task:

Write the reaction to produce cholesteryl oleate from cholesterol and oleic acid.

Esterification Reaction
Reaction:
Cholesterol + Oleic acid β†’ Cholesteryl oleate + Hβ‚‚O

Enzymatic: Cholesterol + Oleoyl-CoA β†’ Cholesteryl oleate + CoA-SH
(Enzyme: ACAT)
Cholesterol
Cholesteryl Oleate
IUPAC: (3Ξ²)-cholest-5-en-3-yl (9Z)-octadec-9-enoate
Transport: Core of LDL/HDL particles
Problem 7: Taurocholic Acid Formation
πŸ“‹ Task:

Write the reaction between cholic acid and taurine to form taurocholic acid.

Bile Acid Conjugation
Reaction:
Cholic acid + Taurine β†’ Taurocholic acid + Hβ‚‚O

Enzymatic: Requires ATP and CoA activation
Cholic Acid
Taurocholic Acid
Class: Conjugated bile acid
Function: Fat emulsification, micelle formation
Role: Emulsifies dietary fats in small intestine, increases surface area for lipase

End of Topic 5 Solutions

All lipid structures shown as components + complete molecules for better understanding.