A flow chart shows how fats and proteins enter the respiratory pathway: glucose to pyruvic acid to acetyl CoA to the Krebs cycle. A fat is broken into glycerol and fatty acids. Glycerol joins the pathway at point A after being changed into one compound, and fatty acids join at point B after being broken down. Which option names A and B?
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Fats break down into glycerol and fatty acids. Fatty acids are degraded to acetyl CoA, and glycerol is converted to PGAL, a glycolytic intermediate. Because the pathway is used for both breakdown and synthesis, it is called amphibolic.
- A.
The entry points are swapped. Glycerol is converted to PGAL, and fatty acids are degraded to acetyl CoA.
- B.
Glycerol enters as PGAL. Fatty acids enter as acetyl CoA, not as a Krebs cycle acid like oxaloacetic acid.
- D.
Glycerol does not enter as glucose, and fatty acids are first degraded to acetyl CoA before entering the Krebs cycle.
NCERT: Class 11 Biology, Chapter 12