Metabolism of fats Flashcards
What are the 3 sources of fats
De novo biosynthesis in the liver (i.e. from scratch), diet (main) and adipose storage
What does breakdown of triacylglycerols allow?
Fatty acids form, which can convert to acetyl CoA for the TCA cycle
What is the function of bile salts?
To emulsify fats (make soluble) so fats can be digested and absorbed.
Fat-soluble vitamins e.g. A,D,E & K can be absorbed
Why are fats difficult to digest?
They are amphipathic and hydrophobic, so will not travel well
What does lack of bile salts cause?
Most fat will pass through the gut, forming fatty stool: steatorrhea
What is Orlistat?
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
What are side effects of Orlistat?
Steatorrhea, abdominal pain and urgency to defecate
What are lipoproteins?
Carriers produced by the liver, that transport lipids/FAs in the plasma, within their hydrophobic core
What is an apoprotein?
A protein that, with a prosthetic group, forms a particular biochemical molecule
What is the structure of a lipoprotein?
A phospholipid monolayer with cholesterol and apoproteins. This layer surrounds the central hydrophobic core of triacylglycerols and cholesterol esters
What is the function of cholesterol esters in the core of lipoproteins?
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.
What is chylomicron?
The least dense type of lipoprotein
What is the function of chylomicron (CM)?
It transports lipids from intestines to other tissues e.g. adipose, cardiac and skeletal muscle. Here, FFAs can be absorbed by tissues.
Where is CM made?
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.
What happens after a chylomicron “collects” triglycerides?
Via lymphatics, the CMs go into the blood stream. Here, apoproteins from HDLs are acquired into the monolayer, forming a lipoprotein
How does lipoprotein lipase breakdown lipids?
Located in capillary endothelial cells lining tissues, the lipase binds to the recognised apoprotein, which activates the enzyme to hydrolyse the triglyceride.
What happens to the products of triglyceride hydrolysis?
Fatty acids undergo beta-oxidation, whilst glycerol returns to the liver for gluconeogenesis
What is the lifecycle of a lipoprotein?
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.
What is HDL?
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
What is LDL?
Low-density lipoprotein: “Bad” as prolonged elevation causes blocking of arteries (atherosclerosis) as it transports cholesterol made in the liver to peripheral tissues
What is the fate of fatty acids synthesised in the liver?
Packaged into VLDLs for transport, and either undergo oxidation in muscle/liver/heart, or incorporated into adipose (can be used when needed)
What is the function of albumin?
A carrier protein which transports non-esterified fatty acids in plasma- a lipoprotein???
What classes of lipoproteins are made from the liver?
VLDLs for endogenous fat transport (transports triglycerides and cholesterol to muscle and adipose like CMs), and HDLs for reverse cholesterol transport
What are the 3 classes of lipoproteins not made in the liver- explain?
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
