Lecture 12

Question 1

Process of Digestion/Absorption of Lipids:

Answer 1

1. Process initiated by lingual lipase in mouth
2. Continues in the stomach by gastric lipase

2a. Lingual and gastric lipases hydrolyze preferably TGs containing short and medium chain fatty acids (long chain, which are the majority, remain intact until they reach the small intestine)

2b. Fat entering the duodenum is made up of 70% TGs (long chain fatty acids) with the remainder composed of a mixture of partially hydrolyzed lipids products (short & medium chain, and 1,2-DAG; position 1 & 2 are untouched, position 3 has been cleaved)

Question 2

The Role of Co-Lipase in lipid digestion

Answer 2

1. Lipase on its own has the ability to cleave triglycerides, chop fatty acids from glycerol backbone

2.Inhibition by Bile Salts

Question 3

How does the presence of bile salts in the duodenum inhibit lipase activity, and what role does co-lipase play in overcoming this inhibition to facilitate effective lipid digestion?

Answer 3

1. When bile salts from the gallbladder enter the small intestine, they can stop lipase, an enzyme that breaks down fats, from doing its job.

2.Bile salts do this by pushing the lipase away from the surface of fat droplets, so it can’t work properly

3. To fix this issue, the pancreas releases co-lipase along with the lipase.
4. Co-lipase grabs onto the lipase and helps it get back to the surface of the fat droplet. This ensures that lipase stays in the right place to break down fats effectively.

Question 4

what is the Intestinal Lumen

Answer 4

The intestinal lumen refers to the hollow space within the intestines where digestion and absorption of nutrients occur

Question 5

1-MAG & 2-MAG

Answer 5

breakdown product of triglycerides

Question 6

explanation of the absorption of lipids in the intestine:

Answer 6

1. When lipids are broken down into smaller molecules (such as fatty acids and monoglycerides) during digestion, they may have difficulty moving through the watery environment of the intestine. To overcome this challenge, bile acids produced by the liver and stored in the gallbladder help to form micelles.
2. Micelles interact with the microvilli at the brush border and allow the movement of lipids into the enterocytes via protein-dependent and independent processes (some lipids cross cell membrane passively since it is a lipid bilayer)

Question 7

How are lipids transported in the duodenum and jejunum

Answer 7

In the duodenum and jejunum, some lipids are transported from lumen to enterocyte via diffusion, and others are transported via proteins (FATP1-4/CD36, NPC1L1-Chol.)

Question 8

lipids are transported in the blood via various lipoprotein particles, including:

Answer 8

chylomicrons (transport lipids in the intestine)
VLDL (comes from liver)
LDL (product of modification of VLDL)
HDL (comes from liver)

Question 9

What is the role of apoproteins (Apo) in the distribution and exchange of lipids in the body?

Answer 9

Apoproteins dictate the fate of lipoproteins, determining where they will be sent to and what functions they will carry out.

Question 10

How do apoproteins facilitate the transfer of lipids from lipoproteins to cells?

Answer 10

Apoproteins on the surface of lipoproteins act as receptors that connect to cell surface receptors, allowing the transfer of lipids from the lipoproteins to the cells.

Question 11

Why are apoproteins crucial for lipid transport in the bloodstream?

Answer 11

Apoproteins confer water solubility to lipoproteins, ensuring their stability and preventing aggregation in the aqueous environment of the bloodstream.

Question 12

What is the significance of ApoB in lipoproteins such as chylomicrons, VLDL, and LDL?

Answer 12

ApoB, present in chylomicrons, VLDL, and LDL, serves as a receptor ligand on the surface of lipoproteins, allowing them to bind to cells and mediate lipid transfer.

Question 13

How does Apo-E contribute to lipoprotein function?

Answer 13

Apo-E, existing in three isoforms, is present in almost all lipoproteins and plays a role in mediating particle removal from the circulation by binding to specific receptors on cell surfaces.

Question 14

What apoproteins are found in HDL (High-Density Lipoprotein)?

Answer 14

HDL contains apoproteins A-I, A-II, A-IV, and C, among others, which contribute to its functions such as reverse cholesterol transport and antioxidant activity.

Question 15

What is the origin of ApoB-48, and in which lipoproteins is it found?

Answer 15

ApoB-48 originates from the intestine and is found in chylomicrons, with a typical ratio of 1 ApoB-48 per lipoprotein.

Question 16

From where does ApoB-100 originate, and in which lipoproteins is it enriched?

Answer 16

ApoB-100 originates in the liver and is enriched in VLDL and LDL. It is derived from the same gene as ApoB-48 but is a different variant.