Fatty Acid Catabolism

Compare fats and sugars as energy sources.

Fats: long-term storage, slow delivery, more energy per carbon (more reduced), less water.
Sugars: short-term energy, quick delivery, stored as glycogen.

How are fatty acids absorbed and transported?

Emulsified by bile salts in the intestine → packaged into chylomicrons → travel in blood.

Free fatty acids bind to albumin for transport to tissues.

How are fats stored in the body?

Stored in adipocytes: white fat (energy), brown fat (heat generation), beige fat (derived from white fat).

What is lipolysis and how is it regulated?

Lipolysis: breakdown of triacylglycerols into free fatty acids + glycerol.

Activated by glucagon and epinephrine, inhibited by insulin.

Where do the components of triacylglycerol go after breakdown?

Glycerol → glycolysis or gluconeogenesis; fatty acids → β-oxidation for energy.

How are fatty acids transported through the body?

Bind to albumin for circulation and delivery to tissues.

Describe the carnitine shuttle.

Long-chain fatty acids converted to acyl-CoA → transferred to carnitine via CAT I → transported into mitochondria → converted back to acyl-CoA by CAT II.

List and describe the steps of β-oxidation.

1. Dehydrogenation (FADH2 produced)
2. Hydration (adds OH)
3. Dehydrogenation (NADH produced)
4. Thiolysis (releases acetyl-CoA, shortens chain by 2C).

What is the role of the trifunctional protein (TFP)?

Processes long-chain fatty acids (≥12C); catalyzes hydration, dehydrogenation, and thiolysis; facilitates substrate channeling.

What is the ATP yield of one palmitate molecule (C16)?

8 acetyl-CoA, 7 NADH, 7 FADH2 → total ~108 ATP after full oxidation.

How does β-oxidation differ for unsaturated fatty acids?

Requires an isomerase to convert cis → trans double bonds; polyunsaturated fats also require a reductase.

How does β-oxidation differ for odd-numbered fatty acids?

Produces propionyl-CoA → converted to succinyl-CoA (enters citric acid cycle).

What is the role of coenzyme B12 in fatty acid metabolism?

Vitamin B12 (cobalamin) is required for conversion of propionyl-CoA to succinyl-CoA; deficiency causes pernicious anemia.

How do insulin and glucagon regulate fatty acid metabolism?

Insulin (high energy): activates synthesis (dephosphorylates ACC).

Glucagon (low energy): activates breakdown (phosphorylates ACC).

Where does β-oxidation occur in animals and plants?

Animals: mitochondria (ATP generation).
Plants: peroxisomes/glyoxysomes (heat production).

When and where are ketone bodies formed?

Formed in the liver during low glucose (fasting, starvation, diabetes) when acetyl-CoA accumulates.

Why are ketone bodies important for the brain?

The brain cannot use fatty acids; during glucose shortage, it uses ketone bodies

(acetoacetate, β-hydroxybutyrate) for energy.

What happens if ketone levels become too high?

Excess ketone bodies lower blood pH, causing ketoacidosis; high acetone gives fruity breath odor.