Lipid Metabolism-I

Where does TG accumulation occur in mammalian cells?

• Nucleus

• Mitochondria

• Cytoplasm

• Cell membrane

• Endoplasmic reticulum

Answer explanation

TG droplets accumulate in the cytoplasm and can form a large globule, occupying most of the cell volume.

Fatty acids provide more metabolic water due to their:

• Polar nature

• Lower hydration potential

• Higher reduction potentials

• Low energy yield

• Solubility in water

Answer explanation

Fatty acids are highlighted as providing more metabolic water, especially important in winter sleeping animals, due to their higher reduction potentials and anhydrous nature.

During lipid digestion and absorption, triglycerides are broken down into:

• Monoglycerides and diglycerides

• Monoglycerides and free fatty acids

• Glycerol and fatty acids

• Cholesterol and free fatty acids

• Fatty acids only

Answer explanation

triglycerides are hydrolyzed into monoglycerides and free fatty acids.

Lipase enzyme is activated by all of the following, except:

• Ca++ ions

• Soaps

• Bile salts

• Glucose

• Cholecystokinin (CCK)

Answer explanation

Activation of lipase is mentioned in relation to Ca++ ions, soaps, bile salts, and not glucose.

The enzymes of β-oxidation are found in:

• Mitochondria

• Cytosol

• Golgi apparatus

• Nucleus

• Ribosomal ER

Answer explanation

acyl CoA dehydrogenase

enoyl CoA hydratase

3-hydroxyacyl-CoA dehydrogenase

β-ketothiolase

Which enzyme is NOT involved in the beta-oxidation of fatty acids?

• Acyl-CoA dehydrogenase

• Enoyl-CoA hydratase

• Beta-hydroxyacyl-CoA dehydrogenase

• Thiolase

• beta-ketoacyl reductase

Answer explanation

beta-ketoacyl reductase is an enzyme of fatty acid synthesis.

What is the first step in the beta-oxidation of fatty acids?

• Hydration

• Oxidation (Dehydrogenation-I)

• Thiolytic cleavage

• Condensation

• Isomerization

Answer explanation

1- Oxidation-I

2-Hydration

3-Oxidation-II

4-Thiolysis

The first step in beta-oxidation involves the oxidation (dehydrogenation) of fatty acids to form enoyl-CoA. The other options describe either later steps in the process or reactions not involved in beta-oxidation.

Beta-oxidation is regulated by the availability of which molecule in the mitochondrial matrix?

• Oxygen

• Glucose

• Acetic acid

• Carnitine

• Acetyl-CoA

Answer explanation

Carnitine is essential for the transport of fatty acids into the mitochondrial matrix for beta-oxidation. The availability of carnitine can thus regulate the rate of beta-oxidation.

What role does carnitine palmitoyltransferase I (CPT-1) play in fatty acid oxidation?

• Converts acetyl-CoA to malonyl-CoA

• Catalyzes the hydration step

• Converts fatty acyl-CoA to acylcarnitine

• Synthesizes carnitine from lysine and methionine

• Oxidizes NADH to NAD+

Answer explanation

CPT-1 is critical for the transport of fatty acids into mitochondria for oxidation by converting fatty acyl-CoA to acylcarnitine.

During fatty acid oxidation, which compound directly enters the citric acid cycle?

• Acetic acid

• Glycerol

• Acetyl-CoA

• Carnitine

• Acyl-CoA

Answer explanation

Acetyl-CoA, a product of beta-oxidation, directly enters the citric acid cycle for further energy production. The other compounds either are not directly involved in the citric acid cycle or are products/metabolites of different metabolic pathways.