Lipids lecture 2

Question 1

Absorption of dietary lipids

Answer 1

Triglycerols are the main lipid in the diet of a mammal.
Bile salts - secreted in the intestinal lumen coat the lipids in bile salt micelles to emulsify the lipids
Pancreatic lipase - catalyzes the hydrolysis of triglycerolds

Question 2

2 Predominant bile salts

Answer 2

Taurocholate and glycocholate

Question 3

Properties of biles salts

Answer 3

amphipathic
one hydrophobic side and one hydrophilic side

Question 4

Hydrolysis of TAGS

Answer 4

splits into two FA chains and 2 H molecules by pancreatic lipase to form 2 monoacylglycerol

Question 5

Hydrolysis of phospholipids

Answer 5

Hydrolyzed by phospholipase at the C2 position - Fatty acid and lysophosphoglyceride which are absorbed by micelles

Question 6

How are cholesterol esters absorbed

Answer 6

converted to free cholesterol by an esterase

Question 7

Importance of converting triglycerols into monoacyl-glycerol

Answer 7

allows transport across the enterocyte membrane (gut) once crossed membrane they are recombined to triglycerol which is then loaded into chylomicrons which enter the circulation via the lymph duct

Question 8

Chylomicron structure

Answer 8

core - contains the triacylglycerol
and cholesteroyl esters
Coated in phospholipids, phospholipid heads are hydrophilic so can travel around the blood stream eventhough TAGs and cholesterol are insoluble

Question 9

WHat happens when the chylomicrons reach the target tissue

Answer 9

Chylomicrons bind to membrane bound lipases on the surface of adipose and muscle tissue which releases the fatty acids and monoacyl-glycerol so that TAGs can be regenerated for storage and the fatty acids can also be broken down for energy generation

Question 10

release of fatty acids from storage at the adipocyte

Answer 10

Controlled by epinephrin hormone
It is detected by the beta Adrenergic receptor. This activates protein kinase A (inactive ) which is converted to active protein kinase A. Protein kinase A phosphorylates hormone sensitive lipase using ATP to form ACTIVE hormone sensitive lipase. The hormone sensitive lipase catalyzes this reaction :

Triacylglycerol - Diacylglycerol - monoacylglycerol - (monoacylglycerol lipase) - glycerol
A fatty acid removed each time

Question 11

What is glycerol used for in the liver

Answer 11

Glycolysis
Gluconeogenesis

Question 12

what are fatty acids used for in the muscle

Answer 12

beta oxidation

Question 13

Hormones used to regulate fatty acid metabolism

Answer 13

Epinepherine -
Stimulates fatty acid release
insulin -
inhibits FA release
Inactivates triacyglycerol lipase

Question 14

Fatty acid beta oxidation

Answer 14

Cyclic
degrades fatty acids 2 carbons at a time

Question 15

3 stages of FA oxidation

Answer 15

Activation of FA
Transport in mitochondria
degradation to two carbon fragments

Question 16

Activation of fatty acids

Answer 16

1) Co enzyme A is added on to the fatty acid chain
2) uses ATP and acyl coA synthase which forms AMP + PPi
3) forms Fatty acyl CoA
this makes it easier to link into later biochemical reactions

Question 17

Transport into mitochondria

Answer 17

Beta oxidation occurs in the mitochondria
1) Fatty acyl CoA reacts with carnitine (enzyme: carnitine acyltransferase)
2) Removes the CoA from the fatty acid and adds the acyl group to the carnitine forming acylcarintine
3) The acylcarinitine travels across the inner mitochondrial membrane by translocase (transmembrane protein) which sucks in the acyl carnitine and throws out L carnitine
4) within the membrane the acylcarnitne is reacted with CoA (carintine acyltransferase) to form fatty acyl CoA again and rest of carnatine is thrown out again to react with another fatty acyl CoA

Question 18

STAGE 3 - beta oxidation reactions

Answer 18

OXIDATION
Fatty acyl CoA - Trans-enoylCoA
- removing hydrogens
- forms FADH2(acyl CoA dehydrogenase)/FAD/ and QH2 used in the electron transport chain
HYDRATION
- Trans-enoylCoA - 3 Hydroxyacyl CoA (2 enoyl CoA hydratase only works between carbon 2 and carbon 3)
OXIDATION
3 Hydroxyacyl CoA - 3-Ketoacyl CoA
Forms NADH
THIOLYSIS
3-Ketoacyl CoA - Fatty acyl CoA + acetyl CoA
the fatty acyl CoA is shortened by two carbons which is put into acetyl CoA which can be used in other processes
goes through the cycle again and again till only left with acetyl CoA

Question 19

How does acetyl CoA enter the TCA cycle

Answer 19

joins with oxaloacetate catalyzed by citrate synthase to form citrate

Question 20

ATP yield in TCA cycle

Answer 20

Oxidation of NADH - 2.5 ATP
Oxidation of QH2 - 1.5 ATP
Complete oxidation of 1 acetyl CoA - 10 ATP

Question 21

How are unsaturated fatty acids oxidised

Answer 21

1) goes through 3 rounds of beta oxidation
2) then catalysed by delta 3,delta2 - Enoyl CoA isomerase which moves the double bond from the 3-4 position to the 2-3 position so it can use the 2 - enoyl hydratase which breaks dwon the chain again and go into the beta oxidaiton cycle
3) however the double bonds restrict movements so it uses Dienoyl - CoA reductase to convert the double bond to a single bond

Question 22

Ketone bodies - formed during starvation

Answer 22

• During starvation lipids are broken down to make Acetyl - CoA
• Formation of Acetyl CoA far exceeds consumption by the TCA cycle but you dont have enough oxalacetate to make citrate. So the oxalacetate builds up in the liver.
• ketones bodies are formed from the excess acetyl CoA
• transported via blood to peripheral tissues where they are converted to Acetyl CoA and used in TCA cycle or excreted in urine