Question

Triacylglycerols are considered the major form of lipid considered as energy reservoirs in animals.

a. What makes this lipid able to give larger amounts of energy when it is catabolized by the cell? Does its structure and components have something to do with it? If yes, how?

b. TAGs are also considered one of the most abundant type of lipid, but they are not components of biological membranes. Why could be the reason why they cannot?

Please explain in simple words thank you.

Answer 1

What are lipid?
Lipids are a group of naturally occurring molecules that include animal fats, vegetable fats, certain vitamins, triglycerides and phospholipids.
What are triglycerides?
Triacylglycerols are stored as fat droplets in large amounts in vertebrate fat cells, and in plants as oils in the seeds. Triglycerides are overwhelmingly the predominant type of lipid found in nature, accounting for 99 percent of lipids in the body and 95 percent of dietary lipids. Triglycerides function in the body mainly as fuels, supplying 9 calories of energy per gram.
Structure of triglycerides.
Triglycerides consist of a glycerol "backbone" along with three fatty acids bonded to the backbone in an ester linkage. Glycerol is a three-carbon molecule. When one of its hydroxyl groups (-OH) loses a hydrogen, a fatty acid can bind to the oxygen in its place, creating a C-O-C (ester) bond. Fatty acids are four to 24 carbons long.
Disadvantages of TAG?
The increased level of TAG in oru blood leads to obesity which eventually causes heart diseases and lifestyle diseases.

What are the functions of triglycerides?
Triacylglycerol is a better stored energy source than polysaccharides because oxidation of triacylglycerols produces more than twice as much energy than the oxidation of carbohydrates.
Though they are hydrophobic, it does not require hydration, thus it saves the organism the energy required to carry the extra water.
Besides storing energy, triglycerides, like all fats, also provide some thermal insulation, which is particularly important for animals and humans living in cold environments.
A)Triglycerides has more energy yield than carbohydrates. Thats why they are used as the storing form. This is due to their structure. They have one chycerol and 3 fatty acids attached. So they can provide large number of Carbon and Hydrogen on breakdown which can be given by a large amount of carbohydrate consumption. A90 kg human has approximately 45 kg of fat. If that amount of carbohydrate is present, he might be 55 kg more.

B) Why they are not found in biological membranes?
Triacylglycerols lack a polar headgroup, so they cannot orient themselves to form a bilayer. To form a bilayer, the non-polar acyl chains of triglycerides would have to be buried in the interior, and the glycerol moiety would have to be at the surface in contact with the wate.
There are some membranes formed by TAG. But it is not structurally good as phospholipids as they are not AMPHIPATHIC.