Triglycerides: Structure & Function
Energy storage
- The long hydrocarbon chains contain many carbon-hydrogen bonds with little oxygen (triglycerides are highly reduced)
- So when triglycerides are oxidised during cellular respiration this causes these bonds to break releasing energy used to produce ATP
- Triglycerides therefore store more energy per gram than carbohydrates and proteins (37kJ compared to 17kJ)
- As triglycerides are hydrophobic they do not cause osmotic water uptake in cells so more can be stored
- Plants store triglycerides, in the form of oils, in their seeds and fruits. If extracted from seeds and fruits these are generally liquid at room temperature due to the presence of double bonds which add kinks to the fatty acid chains altering their properties
- Mammals store triglycerides as oil droplets in adipose tissue to help them survive when food is scarce (e.g. hibernating bears)
- The oxidation of the carbon-hydrogen bonds releases large numbers of water molecules (metabolic water) during cellular respiration
- Desert animals retain this water if there is no liquid water to drink
- Bird and reptile embryos in their shells also use this water
Insulation
- Triglycerides are part of the composition of the myelin sheath that surrounds nerve fibres
- This provides insulation which increases the speed of transmission of nerve impulses
- Triglycerides compose part of the adipose tissue layer below the skin which acts as insulation against heat loss (eg. blubber of whales)
Buoyancy
- The low density of fat tissue increases the ability of animals to float more easily
Protection
- The adipose tissue in mammals contains stored triglycerides and this tissue helps protect organs from the risk of damage
Examiner Tip
It is common to be asked why triglycerides are energy reserves (they store more energy per gram due to their hydrocarbon chains).
