#beta oxidation

Lipolysis and Beta Oxidation

English: Beta oxidation fatty acids Polski: Schemat beta-oksydacji kwasów tłuszczowych Zh-Cn：β-氧化…

       Fatty acids are chains of carbon and hydrogens with a methyl end and a carboxyl end. The methyl end is called the omega end, and carbon 1(alpha) starts at the carboxyl end. There are two main types of fatty acids, saturated and unsaturated. Saturated fatty acids have all single bonds and the maximum amount of hydrogens possible are in the chain. Unsaturated F.A. have at least one double bond in the chain, which takes electron density away from having a hydrogen there, so we are one hydrogen less per double bond. Double bonds can be cis or trans (pertaining to trans fatty acids). Cis bonds occur naturally, while trans bonds occur synthetically through manufacturing processes such as hydrogenation. Trans fats are not very good for the body as the reactions to metabolize produces negative by-products.

      The process starts with adrenaline and glucagon, which binds to hormone receptors and activates adenylate cyclase which then produces a cascade effect in the body to begin beta oxidation. The fatty acids must be activated and then sent into the mitochondrion. The reaction happens in the matrix of the mitochondrion.

      So to begin with fatty acids, we go through the beta oxidation cycle. We need 2 ATP to activate the molecule. This provides the energy to start the iteration of 4 reactions and gives an acyl-CoA molecule. The molecule can then enter the mitochondrion. The Acyl-CoA gets 2 carbon units chopped off through each iteration, and these are transformed into Acetyl CoA with the addition of the CoA molecule. So we have the fatty acid getting two carbons shorter each cycle, with an acetyl CoA as a product. Each cycle also reduces NADH and FADH2 from NAD+ and FAD and we get one of each. The last breakage (iteration) gives us 2 acetyl CoA and only one of NADH and FADH2. We use H2O and CoASH during the reaction.

  To sum up an easy way to calculate products from a fatty acid molecule:

Let’s say we have palmitate which is a 16 carbon chain saturated fatty acid (16:0). We get 8 acetyl CoA from this molecule, which is half the carbons in the chain. So: Acetyl-CoA =  # carbons/2. Simple. Since we have the last step giving two acetyl CoAs from one cycle of beta oxidation, we get one FADH2 and NADH less. So the yield is (#carbons/2 ) - 1. Imagine having 4 carbon units and cutting in half, we get two, 2 carbon units (two acetyl CoA). So the final run gives two acetyl CoA and one of each NADH and FADH2.

Yield from palmitate: Acetyl CoA- 16/2 = 8 Acetyl CoA NADH and FADH2 = (16/2) -1 = 7 NADH and 7 FADH2  

Acetyl CoA then goes through the citric acid cycle. 8 acetyl CoA will go through 8 turns of the C.A.C. Yield of 8 acetyl CoA: 8 x 2 CO2 = 16 CO2 8 x 1 ATP = 8 ATP – 2 for activation = 6 ATP 8 x 3 NADH = 24 NADH 8 x 1 FADH2 = 8 FADH2 We have a total so far of 16 CO2, 6 ATP, 31 NADH (24 from CAC and 7 from Beta oxidation), 15 FADH2 (8 from beta oxidation and 7 from beta oxidation). All this NADH and FADH2 goes into oxidative phosphorylation. Since we get 12 protons pumped from each NADH and 8 protons pumped from each FADH2 molecule: 12 x 24 NADH = 288 protons pumped into the IMS 8 x 15 FADH2 = 120 protons pumped into the IMS 408 total protons pumped into IMS. These protons then go through the ATP synthase which makes 1 ATP from 4 protons. So our yield in ATP: 408/4 = 102 ATP synthesized. The total and final yield from one molecule of palmitate is as follows: 16 CO2, 108 ATP, and H2O. (there are many H2O molecules made but the stoichiometry is not important here).

With trans fatty acids, a reaction can change the bond to a cis bond which is then usable in the beta oxidation cycle (during the cycle). Each double bond imparts one less FADH2 as a product.

      We can see that fatty acids are very energy rich molecules and very important biologically Fatty acids are stored in adipose tissues (fat cells). Fat is easily stored as energy and imparts (from mainly anecdotal sources) about 3 times the energy as sugar does by weight. Glucose is more easily metabolized though.

Fun with Biochem/Organic!

This is the second step in the beta-oxidation pathway of fatty acids. Water breaks the double bond and the OH group adds to the beta carbon, which is the first part of oxidizing the beta Carbon. (Hey, so THAT'S why it's named that!) The beta Carbon is called that because it is two Carbons over from the Carbon with a double-bonded Oxygen. (C=O is called a carbonyl.) The reason this is also fun with Organic is because the Michael Reaction, where a nucleophile (something that donates electrons) attacks the beta carbon rather than the carbonyl, is what I was referring to with the name "Michael Maneuver." This is seen in Organic classes. Professors love to go over that mechanism. I made them soldiers because I think it's hilarious whenever professors say the molecules are "attacking" something.