Metabolism of fats

Question 1

What are the 3 sources of fats

Answer 1

De novo biosynthesis in the liver (i.e. from scratch), diet (main) and adipose storage

Question 2

What does breakdown of triacylglycerols allow?

Answer 2

Fatty acids form, which can convert to acetyl CoA for the TCA cycle

Question 3

What is the function of bile salts?

Answer 3

To emulsify fats (make soluble) so fats can be digested and absorbed.
Fat-soluble vitamins e.g. A,D,E & K can be absorbed

Question 4

Why are fats difficult to digest?

Answer 4

They are amphipathic and hydrophobic, so will not travel well

Question 5

What does lack of bile salts cause?

Answer 5

Most fat will pass through the gut, forming fatty stool: steatorrhea

Question 6

What is Orlistat?

Answer 6

A drug which inhibits pancreatic/gastric lipases. So, fat absorption decreases and more will be excreted as faeces. This combats obesity, but for 2 years only

Question 7

What are side effects of Orlistat?

Answer 7

Steatorrhea, abdominal pain and urgency to defecate

Question 8

What are lipoproteins?

Answer 8

Carriers produced by the liver, that transport lipids/FAs in the plasma, within their hydrophobic core

Question 9

What is an apoprotein?

Answer 9

A protein that, with a prosthetic group, forms a particular biochemical molecule

Question 10

What is the structure of a lipoprotein?

Answer 10

A phospholipid monolayer with cholesterol and apoproteins. This layer surrounds the central hydrophobic core of triacylglycerols and cholesterol esters

Question 11

What is the function of cholesterol esters in the core of lipoproteins?

Answer 11

Made in the plasma from cholesterol using the LCAT enzymes, their acyl tail makes the core more hydrophobic. So, the contents are packed together even more.

Question 12

What is chylomicron?

Answer 12

The least dense type of lipoprotein

Question 13

What is the function of chylomicron (CM)?

Answer 13

It transports lipids from intestines to other tissues e.g. adipose, cardiac and skeletal muscle. Here, FFAs can be absorbed by tissues.

Question 14

Where is CM made?

Answer 14

Enterocytes lining the small intestine, which absorb digested products (brush border). They resynthesise triglycerides to incorporate into the chylomicrons, which is the beginning of lipoprotein synthesis.

Question 15

What happens after a chylomicron “collects” triglycerides?

Answer 15

Via lymphatics, the CMs go into the blood stream. Here, apoproteins from HDLs are acquired into the monolayer, forming a lipoprotein

Question 16

How does lipoprotein lipase breakdown lipids?

Answer 16

Located in capillary endothelial cells lining tissues, the lipase binds to the recognised apoprotein, which activates the enzyme to hydrolyse the triglyceride.

Question 17

What happens to the products of triglyceride hydrolysis?

Answer 17

Fatty acids undergo beta-oxidation, whilst glycerol returns to the liver for gluconeogenesis

Question 18

What is the lifecycle of a lipoprotein?

Answer 18

A VLDL releases FFAs, glycerol and cholesterol to muscles etc., leaving a lipid-depleted remnant. Apoproteins are transferred to HDL, leaving IDL. Cholesterol esters from LDL are added to IDL, forming LDL. LDL is then removed by macrophages and the liver. The liver produced VLDLs again.

Question 19

What is HDL?

Answer 19

High-density lipoprotein: “Good” as it takes cholesterol from peripheral tissues (dead cells or those undergoing turnover) using LCAT, taking it to the liver (REVERSE CHOLESTEROL TRANSPORT) for use/disposal. It lowers total serum cholesterol

Question 20

What is LDL?

Answer 20

Low-density lipoprotein: “Bad” as prolonged elevation causes blocking of arteries (atherosclerosis) as it transports cholesterol made in the liver to peripheral tissues

Question 21

What is the fate of fatty acids synthesised in the liver?

Answer 21

Packaged into VLDLs for transport, and either undergo oxidation in muscle/liver/heart, or incorporated into adipose (can be used when needed)

Question 22

What is the function of albumin?

Answer 22

A carrier protein which transports non-esterified fatty acids in plasma- a lipoprotein???

Question 23

What classes of lipoproteins are made from the liver?

Answer 23

VLDLs for endogenous fat transport (transports triglycerides and cholesterol to muscle and adipose like CMs), and HDLs for reverse cholesterol transport

Question 24

What are the 3 classes of lipoproteins not made in the liver- explain?

Answer 24

CMs from the intestines to transport dietary fats, IDL from VLDLs (precursor to LDL) and LDL from IDL to transport cholesterol. These 3 acquire triglycerides or cholesterol from other lipoproteins