Calculate the number of ATPs generated by completely oxidizing one molecule of tripalmitoylglycerol into CO2 and H2O in muscle tissues.

Answer 1

This was a fun question to think about for me. I'll walk you through how to come up with your answer, & the parts of the cell it is in.

So first, there is a fatty acid transporter on the cell membrane to bring the fat inside the cytoplasm. Inside, there are lipase enzymes that cleave the fatty acids off of the glycerol core molecule.

When all 3 fatty acids are removed, the glycerol will go through glycolysis in three steps: 1. glycerol kinase will phosphorylate it into glycerol-3-phosphate. 2. Glycerol-3-phosphate dehydrogenase oxidizes it into dihydroxyacetone phosphate or DHAP & NADH. 3. DHAP is converted into glyceraldehyde-3-phosphate via triose phosphate isomerase. After this final step it will continue through the rest of glycolysis & produce 2 ATP, & 1 NADH.

To keep everything straight let's add up everything we have so far: We have 2 ATP & 2 NADH.

3 palmitate molecules were removed from the fat via lipases at an earlier step. Oxidation of fats occurs in the mitochondria, so we have to have another transporter to bring the fats from the cytoplasm inside. This transporter is the carnitine-acyl transporter (Which is the rate-limiting step btw). When the fat has entered the mitochondria it can now go through beta-oxidation. B-oxidation is a four step process generating 1, Acetyl-CoA, 1 FADH & 1 NADH, repeated over & over again, so for simplicity I will not repeat myself. Each round of b-oxidation removes 1 moiety of acetyl-CoA, & 1 acetyl-CoA can be produced per 2 carbons of the fat. Palmitate has 16 carbons, which means that 8 acetyl-CoA, 8 FADH, & 8 NADH molecules are produced per palmitate.

Each acetyl-CoA will now enter the Citric acid cycle & produce 1 ATP/GTP, 1 FADH, & 3 NADH. We had 8 acetyl-CoA molecules so multiply those numbers by 8 & we have 8 ATP/GTP, 8 FADH, & 24 NADH.

We have 3 palmitates, so multiply all of that by 3 & we now have 24 ATP/GTP, 24 FADH, & 72 NADH plus the energy we got from glycerol, & plus the energy removed from b-oxidation so let's add all of those together. We have 26 ATP, 32 FADH, & 80 NADH.

Wow, this has been quite a process so far, but we're almost done. Now we need to figure out the amount of ATP from FADH & NADH. Generally, each NADH produces about 3 ATP, & each FADH produces about 2. You can get more precise numbers from your textbooks, & I don't know exactly what your professor prefers, so we'll just use these numbers.

80 NADH x 3 ATP/NADH = 240 ATP

32 FADH x 2 ATP/FADH = 64 ATP

102 + 64 + 26 ATP = 330 ATP.

That was a lot & confusing so recap: we got 2 ATP, & 2 NADH from glycerol. We got 8 NADH & 8 FADH from each fatty acid in b-oxidation, but we had 3 fatty acids so 24 NADH & 24 FADH. We had 24 acetyl-CoA molecules that went through the citric acid cycle to give use 24 ATP, 24 FADH, & 72 NADH molecules. Add everything up & you should get the same numbers.

Just a general hint, & something that is good to remember is that each palmitate molecule can give you 108 ATP. Wow that is a lot more than the 32-36 from glucose, but it happens much slower due to b-oxidation. You also had 6 ATP from glycerol entering glycolysis.

I hope this answer helps you, I spent a lot of time typing everything up to explain it as best as I could. If you liked my explanation you should sign up for tutoring with me & I can help you more with problems just like this & more.

Best of luck to you,

Michael G.