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1. Introduction to Biochemistry4h 34m
2. Water3h 23m
3. Amino Acids8h 10m
4. Protein Structure10h 4m
5. Protein Techniques14h 5m
6. Enzymes and Enzyme Kinetics13h 38m
7. Enzyme Inhibition and Regulation 8h 42m
8. Protein Function 9h 41m
9. Carbohydrates7h 49m
10. Lipids5h 49m
11. Biological Membranes and Transport 6h 37m
12. Biosignaling9h 45m
Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m

Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism

Fatty Acid Oxidation 2

Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism

Fatty Acid Oxidation 2: Videos & Practice Problems

Video Lessons Practice Worksheet

Topic summary

Unsaturated fatty acids undergo beta oxidation, requiring isomerases to reposition double bonds for effective metabolism. Odd-numbered fatty acids yield propanoyl CoA, which is converted to succinyl CoA for entry into the citric acid cycle (TCA). For palmitic acid, the ATP yield from beta oxidation and subsequent TCA is significant, totaling 108 ATP. This highlights the energy efficiency of fatty acids compared to glucose, despite the latter having a higher energy density per weight. Understanding these metabolic pathways is crucial for grasping energy production in biological systems.

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Fatty Acid Oxidation 2

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Fatty Acid Oxidation 2 Video Summary

Unsaturated fatty acids require specific adjustments during beta oxidation due to the presence of double bonds. While trans configurations can proceed without modification, cis configurations necessitate rearrangement. The goal is to position the double bond correctly, typically between the 2nd and 3rd carbon atoms. If the double bond is not in the correct position, an enzyme called isomerase is employed to shift it, allowing normal beta oxidation to continue. However, it is important to note that this rearrangement does not produce FADH₂ since the initial step of beta oxidation, which introduces a double bond, is bypassed.

In cases where multiple unsaturations exist, isomerase may not suffice, and NADPH is required to reduce the double bond. NADPH acts as an electron carrier, similar to NADH, and upon donating electrons, it converts to NADP⁺. Following this reduction, the double bond can be repositioned, allowing beta oxidation to proceed. For fatty acids with odd numbers of carbons, the final round of beta oxidation yields a 5-carbon molecule, which is split into one acetyl CoA (2 carbons) and one propanoyl CoA (3 carbons). The propanoyl CoA must be converted to succinyl CoA, a process that consumes ATP and is essential for its entry into the citric acid cycle (TCA cycle).

When analyzing palmitic acid, a 16-carbon fatty acid, a simple calculation can determine the number of acetyl CoA produced and the rounds of beta oxidation required. The formula is half the number of carbons minus one: (16/2) - 1 = 7 rounds of beta oxidation, resulting in 8 acetyl CoA. Each round of beta oxidation generates 1 FADH₂ and 1 NADH, leading to a total of 7 FADH₂ (yielding 10.5 ATP) and 7 NADH (yielding 17.5 ATP). The 8 acetyl CoA produced enter the citric acid cycle, where each generates additional ATP, FADH₂, and NADH. Specifically, 8 acetyl CoA yield 8 FADH₂ (12 ATP), 24 NADH (60 ATP), and 8 ATP or GTP from the cycle.

In total, the complete oxidation of palmitic acid through beta oxidation and the citric acid cycle results in approximately 108 ATP. This high energy yield raises the question of why glucose is often preferred as an energy source despite the greater ATP yield from fatty acids. The answer lies in the energy density per weight; glucose provides more energy relative to its weight compared to fatty acids, making it a more efficient fuel source in certain metabolic contexts.

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What role do isomerases play in the beta oxidation of unsaturated fatty acids?

Isomerases are crucial in the beta oxidation of unsaturated fatty acids because they reposition double bonds to make them suitable for further oxidation. Unsaturated fatty acids often have double bonds in the cis configuration, which are not ideal for beta oxidation. Isomerases convert these cis double bonds to trans configurations and move them to the correct position, typically between the 2nd and 3rd carbon atoms. This adjustment allows the fatty acid to continue through the beta oxidation pathway. However, this process does not generate FADH₂ because the double bond is not introduced but merely repositioned.

How is propanoyl CoA from odd-numbered fatty acids metabolized?

Propanoyl CoA, produced from the beta oxidation of odd-numbered fatty acids, is metabolized by converting it into succinyl CoA. This conversion involves adding a CO₂ molecule to propanoyl CoA, a process that requires ATP. The resulting succinyl CoA then enters the citric acid cycle (TCA cycle), where it can be further oxidized to produce ATP, NADH, and FADH₂. This pathway ensures that the energy stored in odd-numbered fatty acids is efficiently utilized in cellular metabolism.

Why does beta oxidation of unsaturated fatty acids sometimes not produce FADH₂?

During the beta oxidation of unsaturated fatty acids, FADH₂ is typically produced in the first step when a double bond is introduced between the 2nd and 3rd carbon atoms. However, if the fatty acid already has a double bond that needs to be repositioned by an isomerase, this step is bypassed. Since the double bond is not newly introduced but merely moved, no FADH₂ is generated in this round of beta oxidation. This results in a lower ATP yield compared to the oxidation of saturated fatty acids.

How much ATP is generated from the complete oxidation of palmitic acid?

The complete oxidation of palmitic acid (a 16-carbon fatty acid) generates a significant amount of ATP. Beta oxidation of palmitic acid produces 8 acetyl CoA, 7 FADH₂, and 7 NADH. Each acetyl CoA entering the citric acid cycle yields 1 FADH₂, 3 NADH, and 1 ATP (or GTP). Summing up, beta oxidation and the citric acid cycle together produce 108 ATP from one molecule of palmitic acid. This high ATP yield underscores the energy efficiency of fatty acids as a fuel source.

Why is glucose preferred over fatty acids for quick energy despite fatty acids producing more ATP?

Although fatty acids produce more ATP per molecule compared to glucose, glucose is preferred for quick energy because it has a higher energy density per weight and can be rapidly mobilized and metabolized. Glucose metabolism via glycolysis and the citric acid cycle is faster and more efficient in terms of speed, making it ideal for immediate energy needs. Additionally, glucose can be utilized anaerobically, providing energy even when oxygen levels are low, unlike fatty acids which require oxygen for beta oxidation.