Published by Patrick Mutisya · 14 days ago
Relate the molecular structure of triglycerides to their functions in living organisms.
A triglyceride is formed by esterification of one glycerol molecule with three fatty‑acid molecules.
| Component | Structural Feature | Resulting Property |
|---|---|---|
| Glycerol | Three‑carbon scaffold, each carbon bearing a hydroxyl group (–OH) | Provides a central point for attachment of fatty acids; contributes to polarity at the molecule’s head |
| Fatty‑acid chains | Long hydrocarbon chain (typically 14–22 C) ending in a carboxyl group (–COOH) | Hydrophobic tail; length and degree of unsaturation affect melting point and fluidity |
| Ester bond | –CO–O– linkage formed by condensation of –OH (glycerol) and –COOH (fatty acid) | Stable covalent bond; reduces polarity of the carboxyl group, making the chain non‑polar |
• Saturated fatty acids contain only single C–C bonds → straight chains → tight packing → higher melting point (solid at room temperature).
• Unsaturated fatty acids contain one or more C=C double bonds → kinks → looser packing → lower melting point (liquid at room temperature).
Shorter chains lower the overall melting point and increase the rate of hydrolysis, making the triglyceride a quicker energy source.
cis‑configuration introduces a bend; trans‑configuration behaves more like a saturated chain, affecting fluidity and health implications.
The amphipathic nature of triglycerides (polar glycerol head, non‑polar fatty‑acid tails) underlies several key biological roles.
| Function | Structural Basis | Biological Significance |
|---|---|---|
| Energy storage | High proportion of C–H bonds in fatty‑acid tails → dense energy per gram (\overline{9} kcal g⁻¹) | Provides long‑term energy reserve; mobilised by lipases during fasting. |
| Thermal insulation | Hydrophobic tails form a layer that traps air and reduces heat loss | Important in mammals and birds for maintaining body temperature. |
| Mechanical protection | Compact, non‑polar droplets cushion organs | Protects kidneys, eyes, and other delicate structures. |
| Component of lipid membranes (as phospholipids) | Glycerol backbone can be esterified with two fatty acids and a phosphate‑containing head group → creates a bilayer with hydrophilic exterior and hydrophobic interior | Forms selective barrier controlling substance movement. |
Triglycerides are broken down by lipases into glycerol and free fatty acids. The glycerol enters glycolysis, while fatty acids undergo \$\beta\$‑oxidation:
\$\$
\text{Fatty acid} + \text{CoA} + \text{ATP} \rightarrow \text{Acyl‑CoA} + \text{AMP} + \text{PP_i}
\$\$
Each round of \$\beta\$‑oxidation removes a two‑carbon acetyl‑CoA unit, which then enters the citric‑acid cycle.