24 Questions
Where does most of the fat absorption occur?
Duodenum
By which point in the small intestine are almost all digested lipids absorbed?
Mid-jejunum
What is the stage of food in the small intestine where fat absorption occurs?
Chyme
Which part of the small intestine is responsible for the majority of fat absorption?
The first section of the small intestine
What is the primary site of lipid absorption in the small intestine?
Proximal duodenum
What is the role of translocase in the cell?
To assist in moving another molecule across a cell membrane
What amino acids are used to synthesize carnitine?
Lysine and methionine
Where is carnitine synthesized in the body?
Liver and kidney
What is the general term for a protein that assists in moving another molecule across a cell membrane?
Translocase
How many ATPs are generated when NADH is oxidized in the electron transport chain?
2.5
What is the end product of the cleavage reaction catalyzed by thiolase?
Acetyl-CoA and an acyl-CoA shorter by two carbon atoms
What is the role of thiolase in the process?
To cleave beta-ketoacyl-CoA into two products
What is the change in the number of carbon atoms in the acyl-CoA after the cleavage reaction?
Decreased by two
In which step of the process does the cleavage reaction occur?
Step 4
What is the product of the oxidation of acyl-CoA by an acyl-CoA dehydrogenase?
Δ2-trans enoyl-CoA
What is the coenzyme for the dehydrogenase in the first reaction?
FAD
How many ATP molecules are produced when FADH2 is oxidized in the electron transport chain?
1.5
What is the enzyme responsible for the oxidation of acyl-CoA?
Acyl-CoA dehydrogenase
What is the reduced form of FAD?
FADH2
What is the product of 8 acetyl CoA in terms of ATP?
80 ATP
How many high energy bonds are utilized in the initial activation reaction?
2
What is the net ATP yield from one molecule of palmitate?
106 ATP
What is the ATP yield from 7 FADH2?
10.5 ATP
What is the ATP yield from 7 NADH?
17.5 ATP
Study Notes
Fat Absorption
- Most of the fat absorption occurs in the duodenum, with almost all digested lipids absorbed by the time the chyme reaches the mid-jejunum.
Carnitine
- Carnitine is synthesized from lysine and methionine in the liver and kidney.
- Translocase is a protein that assists in moving molecules across a cell membrane.
Fatty Acid Oxidation
- Step 1: Oxidation by FAD occurs through acyl-CoA dehydrogenase, producing Δ2-trans enoyl-CoA and reducing FAD to FADH2.
- FADH2 generates 1.5 ATP molecules when oxidized in the electron transport chain.
- NADH generates 2.5 ATP molecules when oxidized in the electron transport chain.
Cleavage
- β-Ketoacyl-CoA is split at the β-carbon by thiolase, producing acetyl-CoA and an acyl-CoA shorter by two carbon atoms.
- Each molecule of palmitate yields 8 acetyl-CoA molecules.
Energy Yield
- The energy yield from one molecule of palmitate is:
- 80 ATP from 8 acetyl-CoA molecules
- 10.5 ATP from 7 FADH2 molecules
- 17.5 ATP from 7 NADH molecules
- Gross total energy yield is 108 ATP, with a net yield of 106 ATP after subtracting 2 high-energy bonds used in the initial activation reaction.
Learn about the process of fat absorption in the digestive system, specifically in the duodenum and jejunum.
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