MMT: transport, storage, and utilization of triacylglycerols

Question 1

What is the central regulator metabolite between carbs and fats?

Answer 1

Acetyl CoA

Question 2

Define lipogenesis.

Answer 2

Conversion of glucose to triacylglycerol

Question 3

Define lipolysis.

Answer 3

Conversion of triacylglycerol to fatty acids

Question 4

Define beta oxidation.

Answer 4

Conversion of fatty acids to acetyl CoA

Question 5

Muscle glycogen is used for…

Answer 5

Muscle contraction

Question 6

Liver glycogen is used for…

Answer 6

Replenishing blood glucose between meals

Question 7

What is the basic structure of triacylglycerol?

Answer 7

Glycerol with three fatty acids esterified to OH

Question 8

What is the basic exogenous pathway?

Answer 8

Dietary fats > intestine > tissues

Question 9

What brings fats to the tissues in the exogenous pathway?

Answer 9

Chylomicrons

Question 10

What is the basic endogenous pathway?

Answer 10

Synthesized in the liver > tissues

Question 11

What brings fats to the tissues in the endogenous pathway?

Answer 11

VLDLs

Question 12

What is the function of bile salts?

Answer 12

They emulsify dietary fats in the small intestine, forming mixed micelles

Question 13

What are intestinal lipases?

Answer 13

They degrade triacylglycerols

Question 14

Describe the movement of fats from the intestines to tissues.

Answer 14

1. Bile salts emulsify fats in the small intestine
2. Intestinal lipases degrade triacylglycerols
3. Fatty acids are taken up by intestinal mucosa and converted to triacylglycerols
4. Triacylglycerols are incorporated into chylomicrons
5. Chylomicrons move through the lymphatic system to bloodstream and tissues
6. Lipoprotein lipase converts triacylglycerols to fatty acid and glycerol
7. Fatty acids are oxidized as fuel or esterified for storage

Question 15

When triacylglycerols are packaged into chylomicrons, what is packaged with them?

Answer 15

Cholesterol and apolipoproteins

Question 16

What activates lipoprotein lipase (LPL)?

Answer 16

apoC-II in capillaries

Question 17

What is ApoB-48?

Answer 17

A protein made in the intestinal epithelium that helps get chylomicrons out of the tissue

Question 18

Describe the structure of lipoproteins.

Answer 18

The lipophilic elements are on the inside and charged elements are on the outside. This allows for the transport of lipophilic substances in a hydrophilic environment, and keeps the particles from freely diffusing into membranes

Question 19

How do we regulate where fatty acids go (muscle vs adipose)?

Answer 19

There are different lipoprotein lipases on different capillaries. Muscle LPL has low Km (high affinity) for TG, so they’ll enter muscle in lower concentrations. LPL in adipose has a high Km/low affinity for TG so it is only activated in excess.

Question 20

What is the precursor for triacylglycerol synthesis?

Answer 20

Glycerol-3-phosphate

Question 21

Name the major intermediates in triacylglycerol synthesis.

Answer 21

1. Glycerol-3-P
2. Phosphatidic acid
3. Diacylglycerol
4. Triacylglycerol

Question 22

How does the liver make glycerol-3-P?

Answer 22

From glucose via glycolysis or from glycerol

Question 23

How does adipose tissue make glycerol-3-P?

Answer 23

From glucose via glycolysis

Question 24

What enzyme is needed to form glycerol-3-P in the liver and adipose tissue?

Answer 24

DHAP

Question 25

What enzyme is needed to make glycerol-3-P from glycerol in the liver?

Answer 25

Glycerol kinase

Question 26

Describe the cycle of glycerol-3-P and TGs through the liver and tissues.

Answer 26

1. Glucose is converted to G3P and fatty acids, which form triacylglycerols 2. VLDL packages and transports TGs out of the liver 3. VLDL interacts with LPL on tissues 4. TGs break into fatty acids that enter tissues, and glycerol which re-enters the liver. 5. Glycerol can be phosphorylated to reform G3P, and the process restarts

Question 27

Briefly describe the release of TGs stored in adipose tissue.

Answer 27

1. Glucagon binds to a receptor on an adipocyte 2. The Gs pathway is stimulated, forming cAMP and then PKA 3. PKA phosphorylates a hormone sensitive lipase 4. Hormone sensitive lipases transport to lipid droplets in the adipocyte 5. TGs are released into the adipocyte at fatty acids

Question 28

Once fatty acids are released into an adipocyte, how do they travel to tissue?

Answer 28

They’re transported into the bloodstream and carried by serum albumin. From there, the fatty acids encounter fatty acid transporters that can take them to various tissues

Question 29

What does adipose triglyceride lipase do?

Answer 29

Convert triacylglycerol to diacylglycerol, releasing fatty acid

Question 30

What does hormone-sensitive lipase do?

Answer 30

Convert diacylglycerol to monoacylglycerol, releasing fatty acid

Question 31

In the fasting state, how do we make G3P?

Answer 31

Via amino acids and gluconeogenesis

Question 32

What is the primary source of G3P in the fed state? Fasting?

Answer 32

Glucose; amino acids

Question 33

Insulin helps us ___ fuel.

Answer 33

Store

Question 34

Glucagon helps us ___ fuel.

Answer 34

Utilize