L23- Intro to Lipid Metabolism

Question 1

Carbons in fatty acids are numbered from the _____ (functional group) carbon towards the terminal _____ (functional group) carbon.

Answer 1

Carboxyl, methyl.

Question 2

Where is the beta carbon positioned on a fatty acid chain?

Answer 2

The beta carbon is the 3rd carbon from the carboxyl end.

Question 3

Where is the omega carbon positioned on a fatty acid chain?

Answer 3

The omega carbon is the terminal methyl carbon of the fatty acid chain.

Question 4

What is the difference between unsaturated and saturated fatty acids?

Answer 4

Unsaturated fatty acids contain at least one carbon-carbon double bond, whereas saturated fatty acids contain only single bonds between carbons.

Question 5

Name the essential fatty acids for humans.

Answer 5

Linoleic acid and alpha-linoleic acid.

Question 6

What is the omega number of a fatty acid?

Answer 6

It is the number of carbons from the terminal methyl carbon to the nearest double bond.

Question 7

What is the effect of increasing chain length on the water solubility of fatty acid salts?

Answer 7

The solubility decreases.

Question 8

What is the effect of increasing chain length on the melting point of uncharged saturated fatty acids?

Answer 8

The melting point increases.

Question 9

In general, the addition of two carbons to the tail of a saturated fatty acid increases melting point by how many degrees?

Answer 9

10 degrees Celsius.

Question 10

What the effect of introducing double bonds on the melting point of fatty acids?

Answer 10

The introduction of double bonds decreases the melting point of fatty acids, with trans-double bonds having a greater effect than cis-double bonds.

Question 11

Describe the structure of a triacylglycerol (TAG) molecule.

Answer 11

TAGs consist of three fatty acids, each linked to an OH group on glycerol in an ester bond.

Question 12

What is the major form of storage lipid in cells?

Answer 12

Triacylglycerols (TAGs).

Question 13

Which organ stores and releases bile salts?

Answer 13

The gallbladder.

Question 14

What process breaks down and solubilizes dietary fat in the small intestine?

Answer 14

Emulsification.

Question 15

What is the major function of bile salts in the small intestine?

Answer 15

They act as an emulsifier by coating the surface of fat droplets, thereby solubilizing the fat droplets in water.

Question 16

Which enzyme catalyzes the hydrolytic cleavage of TAGs in the small intestine?

Answer 16

Pancreatic lipase.

Question 17

Pancreatic lipase hydrolyzes TAGs into what products?

Answer 17

Pancreatic lipase cleaves TAG ester bonds in the 1 and 3 position, producing two fatty acids and one 2-monoacylglycerol (2-MAG) molecule.

Question 18

What are two conditions that can cause steatorrhea?

Answer 18

Biliary obstruction and pancreatic diseases that diminish the synthesis of pancreatic lipase.

Question 19

Why is it advantageous for fatty acids to be resynthesized into TAGs in intestinal mucosal cells?

Answer 19

It keeps the free fatty acid concentration in intestinal mucosal cells lower than the concentration in the lumen, allowing for the continued absorption of free acid acids.

Question 20

Which enzymes catalyze the activation of fatty acids to form fatty acyl-CoA derivatives in intestinal mucosal cells?

Answer 20

Fatty acyl CoA synthetase (also called thiokinase) and inorganic pyrophosphatase.

Question 21

Fatty acyl CoA synthetase catalyzes the formation of what kind of bond between fatty acids and coenzyme A?

Answer 21

Thioester bond.

Question 22

What two sequential reactions are catalyzed by fatty acyl CoA synthetase?

Answer 22

The first reaction is the hydrolysis of ATP to generate inorganic pyrophosphate (PPi) and fatty acyl-AMP. The second reaction is the displacement of AMP by coenzyme A to generate an acyl-CoA.

Question 23

What is the approximate Gibbs free energy of the reaction catalyzed by fatty acyl CoA synthetase?

Answer 23

Zero.

Question 24

What drives the reaction catalyzed by fatty acyl CoA synthetase in the forward direction (towards the production of acyl-CoA)?

Answer 24

The cleavage of PPi into 2 Pi by inorganic pyrophosphatase.

Question 25

Which class of enzymes catalyzes the addition of acyl-CoA’s to a molecule of 2-monoacylglycerol in intestinal epithelial cells?

Answer 25

Acetyltransferases.

Question 26

In which compartment of the intestinal cells are TAGs resynthesized?

Answer 26

On the endoplasmic reticulum.

Question 27

In which cellular compartment of intestinal cells are chylomicrons formed?

Answer 27

Between the two phospholipid layers of the ER membrane.

Question 28

The addition of which apoprotein marks the formation of a nascent chylomicron?

Answer 28

Apoprotein B-48.

Question 29

What is the product of the addition of cholesterol to an acyl-CoA?

Answer 29

Cholesterol ester.

Question 30

What is the function of the enzyme acyl cholesterol acyl transferase (ACAT)?

Answer 30

It catalyzes the formation of cholesterol esters from cholesterol and acyl-CoA’s.

Question 31

Why is it advantageous to convert cholesterol to cholesterol ester?

Answer 31

It makes the cholesterol more fat soluble so that it may be packaged in the center of chylomicrons.

Question 32

What is the function of the enzyme cholesterol esterase?

Answer 32

It regenerates cholesterol from cholesterol ester.

Question 33

What enzyme found in serum hydrolyses TAGs completely to fatty acids and glycerol, which can then be taken up by surrounding cells?

Answer 33

Serum monoacylglycerol hydroxylase.

Question 34

Where in the body is the enzyme lipoprotein lipase primarily expressed?

Answer 34

Adipose tissue, skeletal muscle, and on the surface of blood vessels.

Question 35

Which apoprotein functions to activate lipoprotein lipase?

Answer 35

Apoprotein C-II.

Question 36

Which apoproteins on chylomicron remnants bind to LDL receptor-related protein (LRP), or remnant receptor, on the surface of liver cells?

Answer 36

Apoprotein B-48 and apoprotein E.