Why can't fatty acids directly increase blood glucose during fasting?
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Explanation
<strong>Key Takeaways</strong>
<ul>
<li>Fatty acids are broken down to acetyl‑CoA, not to intermediates that can become glucose.</li>
<li>Acetyl‑CoA enters the citric acid cycle but does not regenerate oxaloacetate, which is required for gluconeogenesis.</li>
<li>Without oxaloacetate, the cycle cannot produce the precursors needed to synthesize glucose during fasting.</li>
</ul>
<strong>How to Remember</strong>
<ul>
<li>Mnemonic: **A**cetyl‑CoA **A**lways **A**borts (cannot **A**dd) to oxaloacetate – “AAA” for “Acetyl‑CoA can’t add oxaloacetate.”</li>
<li>Tip: Think of acetyl‑CoA as a “one‑way ticket” into the TCA cycle that never returns the ticket (oxaloacetate) needed to build glucose.</li>
</ul>
2
During beta‑oxidation of palmitic acid, how many molecules of NADH are produced in total (including the citric acid cycle)?
3
Which organ supplies the majority of glucose for the brain during prolonged fasting?
4
What is the primary energetic advantage of using fatty acids over glucose for heart metabolism?
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Explanation
<strong>Key Takeaways</strong>
<ul>
<li>Fatty acids yield more ATP per carbon atom than glucose because they undergo β‑oxidation and generate more reducing equivalents.</li>
<li>The higher ATP yield makes fatty acids the preferred fuel for the heart, which has a high and constant energy demand.</li>
<li>Although fatty‑acid oxidation uses more oxygen overall, the ATP‑per‑carbon advantage outweighs the oxygen cost.</li>
</ul>
<strong>How to Remember</strong>
<ul>
<li>Mnemonic: <em>FAT = More ATP per carbon</em> – think of “FAT fuels the heart with more ATP.”</li>
<li>Tip: Picture the heart as a marathon runner; it chooses the fuel that gives the most energy per bite (carbon), even if it’s a bigger bite.</li>
</ul>
5
Which step of gluconeogenesis directly bypasses the irreversible phosphofructokinase‑1 reaction of glycolysis?
6
During fasting, which amino acids are classified as glucogenic and thus can feed directly into the citric acid cycle?
7
What is the net ATP yield from complete oxidation of one palmitic acid molecule, after accounting for activation cost?
8
Which transport protein facilitates fatty acid entry into mitochondria for β‑oxidation?
9
Why does the brain increase its utilization of ketone bodies during prolonged fasting?
10
In the fed state, excess hepatic glucose is converted to which lipoprotein for export to peripheral tissues?
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