Nutrition: Lipids

Question 1

What are three forms in which we take in dietary fats?

Answer 1

triacylglycerol
phospholipids
cholesterol esters

Question 2

What are the three general things we do with fatty acids and what’s an additional fourth?

Answer 2

1. oxidize to CO2 for enery
2. make phospholipids and sphingolipids for membranes
3. store as triacylglycerol
4. polyunsaturated FAs can be used to make arachidonic acid which has a bunch of synthetic purposes in the body

Question 3

Describe in general terms the stems between eating fats and when the fats enter the blood.

Answer 3

1. Nothing reallly happens until reaches the small intestine when CCK and secretin trigger release of bile salts and pancreatic enzymes
2. bile salts emulsify fats
3. pancreatic lipases break them down
4. breakdown products are brought into epithelial cells
5. packaged in triglycerides that get carried out into the lymph by chylomicrons
6. chylomicrons enter blood via lymphatic duct

Question 4

What do we call the little bits of fat that are emulsified by bile salts?

Answer 4

micells

Question 5

What happen to the bile salts once they’re used?

Answer 5

5% are pooped out and 95% are recycled back into the liver

Question 6

Where does pancreatic lipase cut the triacylglycerols in the diet? What are the products?

Answer 6

It cuts at the first and third fatty acid so that you get two free fatty acids and a 2-monoacylglycerol

Question 7

What happens to the fatty acids and 2-monoacylglycerol once they’re in the gut epithelial cell?

Answer 7

they’re repackaged as triacylglycerol in chylomircrons

Question 8

What fatty acids can bypass the whole chylomicron-through-the-lymph thing and just go right from the epithelial cell into the blood?

Answer 8

short and medium chain fatty acids

Question 9

What breaks the fatty acids off dietary fats in the form of cholesterol esters?

Answer 9

cholesterol esterase (easy)

Question 10

What breaks the fatty acids off dietary fats in the form of phospholipids? Products?

Answer 10

Phospholipase A2

gives the fatty acid and lysophospholipid

Question 11

Describe in general terms how the fatty acids get put onto chylomicrons?

Answer 11

The fatty acids are taken into the SER. the RER synthesizes the ApoB-48 apoporotein and then the fatty acids and ApoB48 get combined in the golgi apparatus to form nascent chylomicrons

Question 12

What related apoportine is encoded by the same gene as ApoB48?

Answer 12

ApoB-100

Question 13

How is the gene differentially transcribed to form ApoB48 ot B100? In what cells?

Answer 13

THrough different RNA editing….

Intestinal epithelial cells insert a stop codon so that only a short version is encoded - ApoB48

The hepatocytes don’t put the stop code in so you get the full transcription - ApoB100

Question 14

What is ApoB100 the marker for?

Answer 14

VLDL

Question 15

After the nascent chylomicrons enter the blood they receive two additional markers. What are they? From what?

Answer 15

ApoCII and ApoE from high density lipoprotein

Question 16

What is the function of ApoCII?

Answer 16

It will activate lipoprotein lipase in the capillary beds of muscle and adipose tissue so those peripheral tissues can cleave off fatty acids from the chylomicron

Question 17

As the chylomicron travels through the blood it gradually become ssmaller and smaller as fatty acids are removed. Eventually it loses it’s ApoCII and thus can no longer donate anymore fatty acids. WHat is it called then and what happens to it?

Answer 17

chylomicron remnant

recycled back to the liver

Question 18

What is the typical fate of the fatty acids, glycerol and cholesterol taken up by the liver from chylomicron remnants?

Answer 18

they’ll be repackaged with ApoB100 as VLDL and then go back out in the blood to deliver fatty acids to tissues

Question 19

Which are bigger, chylomicrons or VLDL?

Answer 19

chylomicrons are much bigger, but the composition of the two are pretty much the same

Question 20

Why are adipose cells able to store fatty acids as TAG in the fed state and not other tissues?

Answer 20

Because the glycerol 3-phosphate backbone can only be produced by glycolysis in adipocytes (fermentation)

Question 21

List the liporptoeins in order of size? What is the relationship between triglyceride cocentration?

Answer 21

Smallest is HDL, then LDL, ILDL, VLDL and then chylomicrons are the biggest - just remember that high density = small size

inverse relationship with triglyceride concentration (HDL has the least TG and chylomicrons have the most)