Question

(91 fatty Acid Metabolism. The reactions of the fatty acid spiral are shown below. Use the description on the left side of the page to classify the reactions and fil in the boxes on the right side of the page Aetivation Step. The activation of the fatty acid begins by the addition of CoA which will carry the fatty acid from the cytosol into the mitochondria. The product, which is a fatty acid with a CoA attached, is known as a fatty acyl-CoA. "Acyl" is a general term used when the group attached to CoA is anything other than two carbons. This activation step is endergonic and requires 1 ATP molecule which is converted to I AMP molecule (2 phosphates are cleaved). This activation step is only performed once for each fatty acid, while steps 1-4 are repeatedly cycled to cleave two carbons from the fatty acid each cycle. HO, Activation Step Step 1. This is the beginning of the "spiral". You should be able to identify this metabolic reaction by comparing it to the reactions shown on the previous page. Try to classify it by noticing the changes from reactants to products. If you need a hint, recall your definitions of oxidation and reduction reactions: • Oxidation: increase C-O bonds OR decrease C-H bonds • Reduction: decrease C-O bonds OR increase C-H bonds Since this is an oxidation/reduction reaction, a cofactor is required, and the type of oxidation will help you identify the proper cofactor. s-CoA Step 1 Classify Reaction: S-COA Step 2. This common metabolic reaction was NOT shown on the previous page. Don't make the mistake of classifying this as an oxidation or a reduction. It may look like an oxidation because there is a new C-O bond, but there an "H" and an "OH" is added. In this type of reaction, a cofactor is typically not necessary, but you must add a compound to provide the "H" and the "OH". Step 2 Classify Reaction: OH S-COA Step 3. This is another metabolic reaction that you should be able to identify by comparing it to the reactions on the previous page. Again, by comparing the reactant and the product and you should note that an alcohol converts to a ketone. Note that this reaction produces the second cofactor that can be used to produce ATP. Step 3 Classify Reaction: Step 4. The last reaction is not a typical metabolic reaction and is a classified as a cleavage reaction. This step requires an extra Co- A as a cofactor and the reaction breaks our substrate into two separate products. The product on the right, acetyl-CoA, continues to stage 3 of metabolism (the citric acid cycle). The product on the left, fatty acyl-CoA is two carbons shorter than the starting molecule. This metabolic process is known as a "spiral" because this molecule proceeds to step 1 again to cleave off two more carbons. More specifically in this example, the fatty acyl-CoA at the bottom of the page will go through the fatty acid spiral 2 more times producing 3 acetyl-CoA molecules. S-COA Step 4 Classify Reaction: S-COA S-COA acetyl-CoA fatty acyl-CoA - 80 -

Answer 1

Fatty acid oxidation:

Activation step: Co-A is added, ATP added, AMP produced

Step 1: Oxidation (decrease in C-H bond taking place); FAD added, FADH2 released

Step 2: Hydration (addition of water provides the H and the OH); H2O added

Step 3: Oxidation (Increased C-O bond, loss of H); NAD+ added, NADH+H released

Step 4: Cleavage reaction (bonds getting cleaved to produce 2 different products); CoA added.

Lipogenesis:

Acetyl CoA forming acetyl ACP step: ACP added, CoA released

Acetyl coA forming malonyl ACP step: ACP and CO2 added (2 chemicals), ATP added, ADP+Pi released, CoA released

Step 1: Condensation (two substrates joining); ACP and CO2 released (2 chemicals)

Step 2: Reduction (H being added); NADPH added, NADP released

Step 3: Dehydration (Loss of OH group and release of water); H2O is released

Step 4: Reduction (C-H bonds increasing); NADPH added, NADP released