Biochemistry - Lipid Metabolism

Question 1

What is the definition of a lipid?

Answer 1

Class of organic molecules with low solubility in water and high solubility in nonpolar solvents.

Question 2

What is an isoprenoid? Name five functions.

Answer 2

Subclass of lipid that includes cholesterol, steroids, and fat-soluble vitamins. Multi-ring structures.

1. Bile acids/salts
2. Membranes
3. Signal molecules
4. Cofactors
5. Fat soluble vitamins

Question 3

Name four functions of fatty acids.

Answer 3

1. Energy storage
2. Membrane formation
3. Signaling molecules
4. Nerve and thermal insulation

Question 4

What does the omega number refer to?

Answer 4

The number of carbons from the omega carbon (the last one) to the nearest double bond.

Question 5

Which carbon on a FA is #1?

Answer 5

The carboxyl carbon

Question 6

What is particularly important about linoleic and linolenic acid? What disease can result from dietary insufficiency?

Answer 6

They are essential FAs (need to get from diet). Disease includes scaly dermatitis, alopecia (hair loss), thrombocytopenia (low platelet count) and cognitive development (in children).

Question 7

What is a PUFA?

Answer 7

Polyunsaturated fatty acid

Question 8

Define medium and long chain FAs.

Answer 8

Medium is 6 to 12 carbons. Long is 14 or longer

Question 9

At physio pH, are FAs deprotonated? If so, what do they end up forming?

Answer 9

Yeah, they form FA salts with Na+ or K+

Question 10

How does one name a FA salt compared to FAs?

Answer 10

The “-ic acid” is replaced with “-ate”

Question 11

How does FA chain length affect solubility.

Answer 11

Inverse proportionality

Question 12

Why are FA salts soaps?

Answer 12

Amphiphatic properties.

Question 13

How do double bonds affect melting temp?

Answer 13

Inversely proportional. Note: introduction of the first double bond makes the biggest difference in melting temp (a monounsaturated FA has a MUCH lower melting temp than the corresponding saturated FA)

Question 14

What types of FAs are readily absorbable in the intestine?

Answer 14

Short and medium chain FAs.

Question 15

What is the predominant type of dietary fat?

Answer 15

Triacylglycerides (90%)

Question 16

How does chain length affect FA melting temp?

Answer 16

Directly proportional

Question 17

What is steatorrhea? Name three potential causes.

Answer 17

Fat in poo.

1. Biliary obstruction
2. Chronic pancreatic disease that decreases pancreatic lipase
3. GI disorders that decrease absorption such as celiac disease.

Question 18

What are micelles? How do they aid in absorption?

Answer 18

They are FA aggregations that have been made soluble by gall bladder bile salts (emulsifiers). Once the FA concentration reaches a threshold (called the Critical Micelle Concentration), micelles form. As FAs diffuse into intestinal epithelia, more FAs are released from the micelle for absorption.

Question 19

Where is lipase found? Does it need a cofactor?

Answer 19

It is found in the mouth, stomach, and small intestine. It needs a cofactor to work when in contact with bile salts (called colipase)

Question 20

Where are bile acids made? From what precursor?

Answer 20

Liver, from cholesterol.

Question 21

Does peristaltic action promote micelle formation?

Answer 21

Yeah

Question 22

What is the product of lipase breakdown of TAGs?

Answer 22

Two FAs and one 2-MAG (monoacyl glycerol)

Question 23

What is a gallstone?

Answer 23

An insoluble cholesterol crystal that forms when bile contains too little soluble salt component

Question 24

Are bile salts re-used? What is this pathway called? Describe the pathway.

Answer 24

Yes, called the enterohepatic circulation. Bile salts make their way down the intestine and go into the hepatic circulation at the terminal ileum - 95% are recovered.

Question 25

Once the TAG components are absorbed into intestinal epithelial cells, what happens?

Answer 25

The TAGs are resynthesized.

Question 26

What is the first step in TAG resynthesis? What enzyme does it?

Answer 26

First step is FA activation with ATP and CoAs-H. Fatty acyl-CoA synthetase does it.

Question 27

What enzyme is responsible for synthesizing TAGs from the 2-MAG and activated FAs?

Answer 27

Triacylglycerol synthetase.

Question 28

Where does TAG synthesis occur?

Answer 28

In the ER membrane.

Question 29

What happens to cholesterol before it can associate with a chylomicron? Why?

Answer 29

Conversion to a cholesterol ester. Cholesterol -OH groups make them too soluble to hang out with TAGs in the chylomicrons.

Question 30

What enzyme converts cholesterol to cholesterol esters? What does the opposite?

Answer 30

Acyl-coA cholesterol acetyltransferase (ACAT). Cholesterol esterase remakes the cholesterol.

Question 31

What is Abetalipoproteinemia, aka Bassen-Kornzweig disease?

Answer 31

Defect in MTP. Results in clumsiness and progressive ataxia, neuropathy and vision impairment develop in later childhood or adolescence, low TAG and cholesterol levels, high % of acanthocytes (star-shaped RBCs)

Question 32

What is the half-life of ingested fatty acids?

Answer 32

~10 minutes

Question 33

Name the nomenclature for the following FAs: Stearic acid, palmitic acid, myristic acid, oleic acid, linoleic acid, linolenic acid.

Answer 33

Stearic acid: 18:0
Palmitic acid: 16:0
Myristic acid: 14:0
Oleic acid: 18:1 delta9
Linoleic acid: 18:2 delta 9,12
Linolenic acid: 18:3 delta 9,12,15

Question 34

Which apoprotein binds LDL-R?

Answer 34

B-100