Chapter 4-7. Lipid Synthesis
Recommended Post : 【Biology】 Chapter 4. Cells and Energy Metabolism
2. Anabolism
1 . Acyl-Carnitine Cycle
⑴ 1st. Formation of Acetyl-CoA from Pyruvate in the Mitochondrial Matrix
① Saturated Fatty Acids
○ Acyl coA synthetase on the outer mitochondrial membrane forms acyl-coA by attaching coA to fatty acids after removing ppi from ATP
○ ppi is broken down into 2pi by pyrophosphatase
○ Carnitine acyltransferase 1 on the outer membrane replaces coA with carnitine
○ Acyl carnitine is transported by translocase in the inner membrane
○ Acyl carnitine is converted back to acyl coA by carnitine acyltransferase 2 in the inner membrane
○ Acyl coA → trans-Δ2 enoyl coA → L-3-hydroxyacyl coA (enzyme **: **acyl coA dehydrogenase)
○ L-3-hydroxyacyl coA → 3-ketoacyl coA (enzyme : L-3-hydroxyacyl coA dehydrogenase)
○ 3-ketoacyl coA → acyl coA (n-2) + acetyl coA (enzyme : β-ketothiolase)
② Unsaturated Fatty Acids
○ Isomerase and reductase are additionally involved, producing propionyl coA and succinyl coA
○ propionyl coA (3C) + HCO3- → methylmalonyl coA (4C) (enzyme : propionyl coA carboxylase)
○ methylmalonyl coA (4C) → succinyl coA (enzyme : mutase)
⑵ 2nd. Acyl-Carnitine Cycle : Acetyl-CoA cannot pass through the mitochondrial inner membrane
① 2nd - 1st. Acetyl-CoA + Oxaloacetate → Citrate
② 2nd - 2nd. Citrate can directly pass through the mitochondrial inner membrane
③ 2nd - 3rd. Decomposes into oxaloacetate and acetyl-CoA in the cytoplasm
2. Anabolism
⑴ Anabolism 1. Fatty Acid Synthesis
① Animal Cells : In the cytoplasm, acetyl-CoA utilizes ATP and NADPH for fatty acid synthesis
○ In animal cells, NADPH is synthesized via the pentose phosphate pathway(pentose pathway)
○ acetyl coA + ATP + HCO3- → malonyl coA + ADP + Pi
○ Enzyme : acetyl coA carboxylase
○ Cofactor : Biotin
② Plant Cells : Fatty acid synthesis occurs in the chloroplasts, plastids
⑵ Anabolism 2. Saturated Fatty Acid Synthesis
① Animal Cells
○ In the cytoplasm, lipids can be synthesized up to C-16, which is palmitic acid, in terms of carbon number.
○ The elongation of palmitic acid into longer fatty acids occurs in the smooth endoplasmic reticulum and, to some extent, in mitochondria
② Type 1. Lauric acid : (12 : 0)
○ 12 carbons, 0 double bonds
③ Type 2. Myristic acid : (14 : 0)
○ 14 carbons, 0 double bonds
④ Type 3. Palmitic acid : (16 : 0)
○ 16 carbons, 0 double bonds
⑤ Type 4. Stearic acid : (18 : 0)
○ 18 carbons, 0 double bonds
⑶ Anabolism 3. Unsaturated Fatty Acid Synthesis
① Animal Cells : Desaturase enzymes that form double bonds are located in the smooth endoplasmic reticulum
② Plant Cells : Desaturase enzymes that form double bonds are located in the smooth endoplasmic reticulum and chloroplasts
③ Type 1. Palmitoleic acid : (16 : 1)
○ 16 carbons, 1 double bond
○ ω-7 : First alkene formation at the 7th carbon from the methyl end
④ Type 2. Oleic acid : (18 : 1)
○ 18 carbons, 1 double bond
○ ω-9 : First alkene formation at the 9th carbon from the methyl end
⑤ Type 3. Linoleic acid : (18 : 2)
○ 18 carbons, 2 double bonds
○ ω-6 : First alkene formation at the 6th carbon from the methyl end
⑥ Type 4. α-Linolenic acid : (18 : 3)
○ 18 carbons, 3 double bonds
○ ω-3 : First alkene formation at the 3rd carbon from the methyl end
○ Found in vegetables and vegetable oils (corn oil)
○ Prevents skin diseases and has growth factors
⑦ Type 5. Arachidonic acid : (20 : 4)
○ 20 carbons, 4 double bonds
○ ω-6 : First alkene formation at the 6th carbon from the methyl end
○ Found in animal fats and prevents skin diseases
⑧ Omega 3 Fatty Acids
○ Unsaturated fatty acids forming the first alkene at the 3rd carbon from the methyl end
○ Promote red blood cell aggregation and prostaglandin production, preventing heart disease : Also thought to prevent cancer
○ EPA, DHA : Omega 3 fatty acids abundant in fish
○ DHA : Good for brain development in young children
⑨ Linoleic acid → Arachidonic acid
⑩ Arachidonic acid → PG, Thromboxane
○ Mediating enzyme : C.O.X
○ PG : Increases blood clotting, headaches, uterine contractions, set point, and gastric mucosa formation
○ Thromboxane : Forms platelets
○ Arachidonic acid → Leukotriene
○ PG, Thromboxane, Leukotriene : Self-decomposing
⑷ Anabolism 4. Cholesterol Synthesis
Figure. 1. Cholesterol Synthesis
① Cholesterol synthesis reaction : Occurs in the liver
○ Step 1. 2 × acetyl-CoA → acetoacetyl CoA
○ Step 2. acetyl-CoA + acetoacetyl CoA + H2O + 2NADPH → HMG-coA (cytoplasm)
○ Step 3. HMG-coA → mevalonate : Rate-determining step
○ Step 4. Formation of isoprene (C5) : Mevalonate → isopentenyl pyrophosphate (PPP) by decarboxylation
○ Step 5. isopentyl pyrophosphate (C6) → squalene (C30)
○ Step 6. Cyclic formation of squalene → cholesterol
② Cholesterol acts as a precursor for various substances
○ Bile salts
○ Steroid synthesis
○ Cholesterol → Androstenedione → (Aromatization) → Estrone
③ Mitochondria : Mevalonate → HMG-coA → acetoacetyl coA + acetyl coA (decomposition reaction)
④ Bacteria lack the ability to synthesize cholesterol
○ Instead, they produce hopanoids to regulate membrane fluidity
○ However, Mycoplasma obtains cholesterol from the environment and uses it to regulate membrane fluidity
⑸ Anabolism 5. Ketone Body Synthesis
① Ketone bodies form when acetyl-CoA accumulates
② Ketone bodies are converted back to acetyl-CoA in the brain, heart, kidneys, etc., and used to generate ATP
⑹ Anabolism 6. Phospholipid Synthesis
① 1st. Fatty acids move to the smooth endoplasmic reticulum membrane
② 2nd. Converted to fatty acid acyl-CoA
③ 3rd. G3P synthesized in the cytoplasm moves to the smooth endoplasmic reticulum membrane.
④ 4th. A substituent combines with two fatty acid acyl-CoAs in the smooth endoplasmic reticulum membrane to form phosphatidic acid.
⑤ 5th. Phosphatidic acid is used for the synthesis of triacylglycerol or phospholipids
Entry: 2019.03.28 13:38