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Burning fat by twos

Science · Biochemistry & Molecular Biology · ages 20-22

Name ______________________ Date ____________

Why can humans not convert fat into net glucose?
- Fat contains no carbon atoms at all
- Acetyl CoA cannot become pyruvate, and the cycle vents as much carbon as it takes in
- Gluconeogenesis refuses all materials except sugar
What does one round of beta oxidation produce?
- One acetyl CoA plus one NADH and one FADH2, with the chain two carbons shorter
- One glucose plus two ATP with the chain unchanged
- One ketone body plus one amino acid directly
What triggers ketone body production?
- Oxaloacetate shortage, so acetyl piles up faster than the cycle can use it
- Extra protein in the diet, whatever the cycle state
- Cold weather slowing down the electron chain
Why do ketones rise during starvation?
- Oxaloacetate is diverted to glucose making, leaving acetyl with nowhere to go
- Starving bodies burn no fat at all
- The brain stops using any fuel during fasting
A 6-carbon fatty acid is chopped two carbons at a time until only acetyl units remain. How many rounds of beta oxidation does that take?
Answer: ______________
Which cells cannot burn ketone bodies, and why?
- Muscle cells, since they lack any enzymes
- Red blood cells, since they lack mitochondria
- Liver cells, since they make ketones
Fat yields more ATP per carbon than sugar because each round also loads electron carriers.
Circle one: True False
A fasting patient shows high ketones with normal fat intake. What explains it?
- Excess dietary fat flooding the liver
- A broken beta oxidation that makes extra acetyl
- Oxaloacetate diverted to glucose making, stranding acetyl CoA

Answer key

For grown-ups. Fold this page away before handing over the rest.

Burning fat by twos W1-mt_2GNrC-0ziR-s1

Acetyl CoA cannot become pyruvate, and the cycle vents as much carbon as it takes in · Fat carbon stops at acetyl with no road to pyruvate. The cycle breathes out whatever the acetyl brings.
One acetyl CoA plus one NADH and one FADH2, with the chain two carbons shorter · Two carbons leave as acetyl while two carriers load up. The chain shortens by exactly two.
Oxaloacetate shortage, so acetyl piles up faster than the cycle can use it · Stranded acetyl is the trigger. Short cycle capacity parks the surplus as ketones.
Oxaloacetate is diverted to glucose making, leaving acetyl with nowhere to go · Fasting steals oxaloacetate for glucose, stranding acetyl. The liver parks the surplus as ketones for the brain.
2 · Rounds equal carbons divided by two, minus one. Six gives three acetyl units across two rounds.
Red blood cells, since they lack mitochondria · Burning ketones needs mitochondria. Red blood cells carry none, so they pass ketones by.
True · Every chop loads NADH and FADH2 on top of acetyl. Carriers plus cycle output beat sugar per carbon.
Oxaloacetate diverted to glucose making, stranding acetyl CoA · Normal intake rules out a fat flood. Diversion during fasting strands even ordinary acetyl flows.