SCT II - Lipid Metabolism I Flashcards
Which two processes take place at the endoplasmic reticulum?
Elongation & Desaturation
Which process takes place in the mitochondrial matrix?
Breakdown of fatty acids (β-oxidation)
What is TAG?
TAG = Lipid
What is Acyl?
Acyl = Fatty acid
Which vitamins are lipid soluble?
Vit. A
Vit. D
Vit. E
Vit. K
What is the simplest fatty acid?
Palmitate (16 C)
What are essential fatty acids?
Fatty acids with double bounds beyond the 9th carbon
Where are steroids made?
Starts in cytosol, then into ER
What transporter transports Citrate?
Tricarboxylic acid transporter
How is Acetyl-CoA transported outside the mitochondrial matrix?
What is the rate limiting reaction of fatty acid synthesis?
What is the effect of insulin/glucagon on Acetyl-CoA Carboxylase?
Insulin
Induces dephosphorylation; activating the enzyme
Glucagon
Induces phosphorylation; inhibiting the enzyme
Name the inhibitors of Acetyl-CoA Carboxylase
Inhibition via Phosphorylation
1. cAMP (Activates Protein Kinase A, which phosphorylates)
2. AMP-Activated Kinases (AMP-Kinase)
3. Low ATP
Name the allosteric regulators of Acetyl-CoA Carboxylase
Allosteric Activators
1. Citrate (+ve Feedback)
2. Thyroid Hormone
Allosteric Inhibitors
- C16-C18 Fatty Acids
What are the properties of the enzyme Fatty Acid Synthase?
- It is a dimer
- It has 3 domains
Each domain contains an individual enzyme
What does the first domain of Fatty Acid Synthase contain?
3 Subunit Enzymes:
1. Malonyl-CoA Transferase
2. Condensing enzyme
3. Acetyl-CoA Transferase
What does the second domain of Fatty Acid Synthase contain?
3 Subunit Enzymes
1. Ketoacyl-CoA Reductase
2. β-Hydroxyacyl-CoA
3. Enoylacyl-CoA Reductase
What does the third domain of Fatty Acid Synthase contain?
1 Subunit Enzyme: Thioesterase
What carrier transports the acyl group from the first domain to the second?
ACP = Acyl Carrier Protein
What is the function of Thioesterase?
To hydrolyze the bond between Palmitate (16C) & ACP (Acyl-Carrier-Protein) so that it’s a free fatty acid
Draw the reactions that take place in the first domain of the Fatty Acid Synthase enzyme!
Draw the reactions that take place in the second domain of the Fatty Acid Synthase enzyme!
Draw the reactions that take place in the third domain of the Fatty Acid Synthase enzyme!
What are the three main steps of fatty acid synthesis?
- Reduction
- Dehydration
- Reduction
What are the three main steps of fatty acid degredation?
- Oxidation
- Hydration
- Oxidation
What is the use of NADPH in lipid metabolism?
NADPH serves as an electron donor in reduction (fatty acid synthesis)
Which substances does Fatty Acid Synthase depend on?
- Pantothenate (Vit. B5)
- Thiol of Phosphopantotheine
- Cysteine residue of Condensing Enzyme
What is another name for the Condensing Enzyme?
β-Ketoacyl-Synthase
What is the main difference between the elongation in the mitochondria and the elongation in the endoplasmic reticulum?
Endoplasmic Reticulum
Polyunsaturated fatty acids are elongated more
Mitochondria
Saturated fatty acids are elongated more
What is the equation of elongation in the endoplasmic reticulum?
What is the equation of elongation in the mitochondria?
Where does carbon desaturation take place?
Membrane of endoplasmic reticulum
What is desaturation?
Addition of a double bond
What carbon positions can humans desaturate?
4,5,6, and 9
Name the three desaturation enzymes
- NADH-eyt b3 Reductase (Cytochrome b5 Reductase)
- Cytochrome b5
- Desaturase
When is a compound saturated?
When it has no double bonds
What is the ratio of NADH and double bonds in desaturation?
NADH:Double-bond (1:1)
Draw the pathway of the desaturation of a saturated fatty acid
Name the two important essential fatty acids
Omega-3: Linolenic Acid
Omega-6: Linoleic Acid
Which protein surrounds a TAGs in an adipocyte?
Perilipin
What is the effect of Glucagon on TAG degradation?
How many fatty acids can bind to albumin?
3
What is another name for free fatty acids?
Non-esterified fatty acids
When is a fatty acid activated?
When it is bound to CoA
What is the enzyme responsible for the activation of fatty acids?
Fatty Acyl-CoA Synthetase
Is the activation of fatty acids an energetic or non-energetic process?
Uses ATP
Where does fatty acid degradation (β-oxidation) take place
Mitochondrial matrix
What number of carbon having fatty acid can pass by the inner mitochondrial membrane?
less than 12 via passive diffusion
What does CPT stand for?
Carnitine-Palmitoyl-Transferase
Which CPT is in IMM and OMM?
OMM = CPT I
IMM = CPT II w/ Translocase
β-oxidation pathway
Fatty Acyl-CoA Dehydrogenase (FAD to FADH2)
What is the ratio of product after degradation of an even carbon fatty acid?
2:1 (16C:8AcetylCoA)
What is the ratio of product after degradation of an odd carbon fatty acid?
2:1 (17C:8AcetylCoA + 1Propionyl-CoA)
What is the final product of one β-oxidation cycle?
1 FADH2
1 NADH
1 Acetyl-CoA
Name all lipoproteins needed for fatty acid transport
CM: Chylomicron
VLDL: Very low density lipoprotein
IDL: Intermediate density lipoprotein
LDL: Low density lipoprotein
HDL: High density lipoprotein
In lipoproteins, what is the density (inversely) proportional to?
Density prop. to protein content
Density inv. prop. to lipid content
What is the function of chylomicron (CM)?
Transport of TAG absorbed from intestines through blood
What is the function of LPL?
LPL is the middle man between tissue and Chylomicron, it takes what it needs and Chylomicron remains in blood till it’s fully taken from multiple LPL
Where is the final destination of chylomicron?
Liver, deposits whatever fat is left via LRP1 RECEPTOR
Which apoprotein does LDLR bind?
ApoB-100
Which apoprotein does the LRP1 bind?
ApoE
What is the exogenous pathway?
Transport of absorbed lipids TO THE LIVER
What is the endogenous pathway?
Transport of synthesized lipids FROM THE LIVER to TISSUE then BACK TO THE LIVER
Can free fatty acids float in blood?
No, they bind to albumin
