Lipid Digestion

Question 1

Does lipid digestion occur in the mouth? Explain why/why not.

Answer 1

The water soluble enzymes do not breakdown the non-polar fat and oil in the mouth.
However, the mouth contains a small amount of lingual lipase (non-polar enzyme) that does breakdown some of the ester connections within the triacylglycerol (TAG).

Question 2

What role(s) does the stomach play in lipid digestion? 
Are any enzymes present?
If so what do the enzymes do?

Answer 2

Once the fat/oil enters the stomach it separates into smaller droplets within the
chyme, which makes the fat/oil easier to digest.
The stomach also contains gastric lipase enzymes, which can break some of the ester bonds within TAG.
Most of the breakdown of TAG occurs in the small intestine.

Question 3

How do the pancreatic lipases convert triacylglycerol (TAG) into MAG and fatty acids in
the small intestine?
Explain how the monoacylglycerol (MAG) and fatty acids are used to
generate micelle’s.

Answer 3

The pancreatic lipase enzymes break down TAG into MAG and two fatty acids (in the small intestine), by cutting two of the ester connections between the glycerol and the fatty acids (within TAG).
The MAG and fatty acids then associate together to
form spherical micelle structures, which have a polar outer shell (glycerol and carboxylic acid group in the fatty acid) and a non-polar centre (fatty acid tails).

Question 4

Once micelles are absorbed into the intestinal cells they
require repackaging.
What role do the micelles have in creating the chylomicrons (deliver TAG into the bloodstream)?

Answer 4

Once inside the intestine cells, the micelles are broken down into the MAG and fatty
acid components.
Ester bonds are formed to link the MAGs to the fatty acids in
order to create TAG.
Many TAGs combine with protein, cholesterol and
phospholipids to from chylomicrons, which are carried into the blood stream via the lymphatic system.

Question 5

Discuss how and under what circumstances the TAG would be stored

Answer 5

When TAG is not required to generate ATP (energy needs of the body have been
met), the TAG will be transported to an adipocyte (within the adipose tissue) to be stored as fat.

Question 6

Discuss how and under what circumstances TAG would be metabolised.

Answer 6

When TAG is required to generate ATP (to meet the energy needs of the body),
the TAG is broken down into fatty acids and glycerol by lipoprotein lipases (present
in the lining of the blood vessels near tissue).
Once inside the cell, the fatty acids and glycerol are metabolised to generate ATP the relevant various metabolic reactions.