Fat Transportation

Question 1

Fatty acids and glycerol are further broken down into what?

Answer 1

Fatty acids into Acetyl CoA and glycerol used for gluconeogenesis.

Question 2

Where is the majority of ATP synthesised and why?

Answer 2

The mitochondria as the formation of acetyl CoA forms ATP and acetyl CoA is produced from both types of major food molecules, fats and sugars.

In addition to this, oxidative phosphorylation from the reduced NADH, FADH2 also produce a lot of ATP

Question 3

Where are the 3 main sources of fat?

Answer 3

The diet
De novo biosynthesis (liver)
Storage depots in adipose

Question 4

A lack of bile salts results in what?

Answer 4

The majority of fat passing through the gut undigested and unabsorbed, resulting in steatorrhea (fatty stool).

Question 5

Where are bile salts generated and stored?

Answer 5

Formed from cholesterol in the liver, stored in the gall bladder.

Question 6

How do bile salts aid in the digestion of fats?

Answer 6

They pass from the bile duct into the intestine where they emulsify the fats, helping the body to break them down and absorb them and also the fat soluble vitamins (A,D,E,K)

Question 7

What is orlistat (tetrahydrolipstatin)?

Answer 7

A potent inhibitor of gastric and pancreatic lipases and so a powerful fat loss treatment (reduces fat absorption by 30%, works for up to 2 years)

Question 8

What are the 4 main side effects of orlistat?

Answer 8

Abdominal pain, urgency to defecate, increased flatus and steatorrhea.

Question 9

How are lipids transported around the body?

Answer 9

Lipoproteins such as :
CM (Chylomicrons), 
VLDL (Very Low Density Lipoproteins), 
IDL (Intermediate Density Lipoproteins), 
LDL (Low Density Lipoproteins),
HDL (High Density Lipoproteins)

Question 10

What are digested dietary products absorbed by?

Answer 10

Enterocytes that line the brush border of the small intestine.

Question 11

What must happen before triglycerides absorbed are incorporated into chylomicrons?

Answer 11

Triglycerides must be resynthesized under the control of several enzymes.

Question 12

What happens to CMs after incorporating triglycerides?

Answer 12

They are transported via the lymphatic and on into the bloodstream. They acquire apoproteins from HDL following release into the bloodstream.

Question 13

How do CMs enter the bloodstream?

Answer 13

Travel from the lacteals of the small intestine to the thoracic duct and to the left subclavian vein where they enter the bloodstream.

Question 14

How do the apoproteins allow the nutrients in a CM to enter cells?

Answer 14

Apoproteins bind to lipoprotein lipase receptors on the capillary endothelial cells which line a variety of tissues including adipose, heart and skeletal muscles.

Question 15

What happens to the fatty acids and glycerol once in a cell?

Answer 15

Fatty acids undergo beta-oxidation to form Acetyl CoA.

Glycerol returned to liver for use in gluconeogenesis.

Question 16

Where are nascent chylomicrons formed?

Answer 16

Intestinal villus

Question 17

How do Chylomicrons acquire apoproteins?

Answer 17

Transferred from HDLs.

Question 18

What happens to CMs once the glycerol and fatty acids have been removed?

Answer 18

More apoproteins transferred from HDLs to allow recognition from liver.
Remnants taken up by liver to form new nascent chylomicrons.

Question 19

What is the anatomy of a lipoprotein?

Answer 19

Phospholipid monolayer containing cholesterol and apoproteins, surrounding a very hydrophobic core of cholesterol esters and triacylglycerols.

Question 20

How are cholesterol esters formed? cholesterolacyltransferase

Answer 20

Synthesised in the plasma from cholesterol and the acyl chain of phosphatidylcholine (lecithin) via a reaction catalysed by lecithin:cholesterol-acyltransferase (LCAT).

Question 21

What is the life cycle of VLDL, IDL, HDL and LDL?

Answer 21

VLDL is stripped of FFA and cholesterol and glycerol, forming a lipid depleted remnant.

Transfer of apoproteins from the lipid depleted remnants to HDLs forms an IDL.

Transfer of cholesterol esters from HDLs onto an IDL forms an LDL.

LDLs are either taken up by macrophages (can be a problem) or the liver.

Question 22

Why are HDLs known as the good cholesterol?

Answer 22

They take cholesterol from peripheral tissues back to the liver for use or disposal, this is known as reverse cholesterol transport.

Question 23

Why are LDLs known as the bad cholesterol?

Answer 23

Prolonged elevation of LDL levels leads to atherosclerosis (hardening of the arteries). More than 40% of their weight is made up of cholesterol esters and they take cholesterol from the liver to peripheral tissues.