6 Lipid Metabolism Flashcards
Q: What’s the general structure for a fatty acid?
A: hydrophilic carboxylic head and hydrophobic hydrocarbon tail
Q: What’s a saturated fatty acid? (3)
A: completed saturated with H
No double bonds
Completely straight
Q: What’s does an unsaturated fatty acid contain? Shape?
A: double bond
Db inhibits rotation around the bond = kink in chain
Q: What form are fatty acids stored in?
A: triacylglycerols (triglycerides)
Q: Which cells in mammals are specialised for fat storage?
A: adipocytes
Q: Which is solid and which is liquid?
Saturated fatty acids
Unsaturated
A: solids, liquids
Q: What are the 3 main sources of fats?
A: diet, de novo biosynthesis in liver, adipocytes storage (hydrolysed to give fatty acids and glycerol)
Q: What is the role of bile salts? Generated? Stored? Release?
A: emulsify fats and aid absorption-> Interacts with solute and triacylglycerides due to hydrophobic and hydrophilic ends
Get them into soluble form
Generated in liver
Stored in gal bladder
Secreted into small intestine during digestion
Q: What’s a mixed micelle? (8)
A: mixture of triacyl, diacyl, monoacylglycerols and free fatty acids WITH bile salts, cholesterol, lysophosphatidic acid, fat soluble vitamins
Q: What occurs to mixed micelles after formation? (4)
A: absorbed by enterocytes and triacylglycerols TAGs are resynthesised
TAGs are packed into chylomicrons which enter lymphatic system and join circulatory system
Q: How does the caloric yield of fatty acids differ to that of carbohydrates?
A: FA is double that of carbs
Q: What’s the process of fat metabolism and where does it occur? What does it result in?
A: beta oxidation, mitochondria (outer membrane), acetyl CoA
Q: Summarise the process of beta oxidation using a general equation. Enzyme? What does the reaction use? (2)
A: FA + ATP + HS-CoA -> acyl-CoA + AMP + PPi
E: acyl CoA synthetase
ATP -> AMP
2 high energy bonds used
2 phosphoanhydride bonds used
Q: What is the general formula for acyl CoA?
A: O
II
R— C — S —CoA
Q: How do you move acyl CoA into the mitochondria? Draw a diagram.
A: carnitine shuttle
3 components
- CPTI
- CPTII
- translocase
Q: What occurs in the beta oxidation cycle? Draw a diagram.
A: “Fatty acids are firstly converted within the mitrochondrial matrix into an acyl CoA species via the enzyme Acyl CoA synthetase which requires ATP hydrolysis”
1 fatty acyl CoA is oxidised and FAD reduced to FADH2
2 molecule produced is hydrolysed
E: 3 hydroxyacyl CoA hydrolase
3 product is oxidised and NAD is reduced to form NADH
E: L-3-hydroxyacyl CoA dehydrogenase
4 molecule of acetyl CoA is kicked off by bringing in molecule of CoA
E: beta ketothiolase
Fatty acyl CoA as a result has been shortened by 2 carbons and cycle repeats
Q: What first occurs during the beta oxidation of palmitic acid? What’s the overall equation? Final cycle?
A: first E: acyl CoA synthetase converts into 16 C palmitoyl CoA
Palmitoyl CoA + 7FAD + 7 NAD+ + 7H2O + 7CoA -> 8 acetyl CoA + 7FADH2 +7NADH
On the final cycle (4C fatty acyl CoA intermediate enters cycle) 2 acetyl CoA molecules are produced
Q: What is palmitic acid?
A: saturated fatty acid
Q: How does acetyl CoA enter aerobic respiration and under what circumstances? Why?
A: TCA cycle but only if beta oxidation and carbohydrate metabolism are balanced, oxaloacetate is needed for acetyl CoA entry into the TCA cycle
Q: What occurs if fat breakdown predominates carbohydrate metabolism?
A: acetyl CoA forms
Q: Name 3 ketone bodies?
A: Acetoacetate
D-3-hydroxybutyrate
Acetone
Q: What is the net ATP production of palmitate beta oxidation compared to aerobic respiration?
A: Palmitoyl CoA + 7FAD + 7 NAD+ + 7H2O + 7CoA -> 8 acetyl CoA + 7FADH2 +7NADH
7 cycles of beta oxidation = 35
8 a CoA = 96
NADH FAD —> 131
-2 ATP used in beginning = 129
Compared to 38
Much more ATP from fatty acid metabolism that glucose metabolism.
Q: What is fatty acid synthesis called?
Describe the process? Involves? (2) Sequential action of? (3) Link?
A: liposynthesis
Decarboxylative condensation reactions involving the molecules Acetyl-CoA and Malonyl-CoA
After each round of elongation, the fatty acid undergoes reduction and dehydration by the sequential action of:
Ketoreducatase (KR)
Dehydratase (DH)
Enol Reductase (ER)
The growing fatty acyl group is linked to an acyl carrier protein (ACP).
Q: What are the differences between fatty acid synthesis and fatty acid degradation? Type of reaction? Carriers? Reducing power?
A:
FAS= synthesis, FAD= beta oxidation
carriers: FAS= ACP, FAD= CoA
Reducing power: FAS= NADPH, FAD= FAD/NAD
Q: Summary equation for lipogenisis for palmitate.
A: acetyl CoA (C2) + 7 malonyl CoA (C3) + 14 NADPH + 14H+ -> palmitate (C16) + 7CO2 + 6H2O + 8CoA-SH + 14NADP+
Q: Where does fatty acid synthesis occur?
A: cytoplasm
Q: Where does fatty acid degradation occur?
A: mitochondria
Q: What does the desaturation of fatty acids require?
A: E action: fatty acyl-CoA desaturases
Q: Recall 2 examples of inborn errors of lipid metabolism.
A: Medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD)
Primary carnitine deficiency
Q: Disorders of fatty acid oxidation arise from mutations in which family of enzymes?
A: acyl-CoA dehydrogenases
Q: MCADD. Inheritance? Test? What happens if they lose their appetite? Treatment?
A: Medium-chain acyl-coenzyme A dehydrogenase deficiency = in born error of lipid metabolism
Autosomal recessive
Part of heel prick test
Patients with loss of appetite may need IV glucose to ensure body isn’t dependent on FA for energy
If diagnosed. Need to avoid fasting and need to have a carbohydrate rich diet
Q: What is the inheritance for primary carnitine deficiency? Treatment? What is carnitine needed for?
A: (in born error of lipid metabolism)
Autosomal recessive
Can get carnitine supplements as treatment
(Carnitine is needed to chaperone acyl group into mitochondrial matrix from the outer mito matrix)
Q: Which 2 enzymes are needed in fatty acid synthesis?
A: Acetyl CoA Carboxylase, Fatty Acid Synthase (FAS)
Q: What are the 7 steps for fatty acid synthesis? (palmitate)
A: 1 acetyl CoA -> Malonyl CoA (3C)
E: Acetyl CoA carboxylase
ATP, HCO3- in and ADP +Pi out
2 Transfer of Malonyl from Malonyl CoA to Acyl Carrier Protein (ACP) to form Malonyl-ACP
E: Malonyl-CoA-ACP Transferase
3 Transfer of acetyl from a CoA species to acyl carrier protien (ACP) to form Acetyl-ACP
E: Acetyl-CoA-ACP Transferase
4 Condensation of acetyl-ACP with malonyl-ACP to form 4C fatty acid species (FAS does this)
E: β-ketoacyl ACP synthase
5 Reduction of Acetoacetyl-ACP to D-3-hydroxybutyryl-ACP
E: β-ketoacyl ACP reductase
6 Dehydration to crotonyl ACP (a.k.a. trans-∆2-Enoyl-ACP
E: 3 hydroxyacyl-ACP dehydrase
7 Further reduction to butyryl-ACP
E: Enoyl-ACP reductase
The process cycles a further six times from step 4-7 to yield the 16C species palmitoyl-ACP, which is hydrolysed to give palmitate and ACPp
