Lipid Metabolism-II

Where does fatty acid synthesis primarily occur in mammalian cells?

• Nucleus

• Mitochondria

• Cytoplasm

• Golgi apparatus

• Endoplasmic reticulum

Answer explanation

Fatty acid synthesis occurs in the cytoplasm of cells, unlike fatty acid oxidation, which occurs in the mitochondria.

What is the role of Acetyl CoA in fatty acid synthesis?

• It is a by-product.

• It is a catalyst.

• It is a precursor.

• It is an inhibitor.

• It is an enzyme.

Answer explanation

Acetyl CoA serves as a building block and starting material in the synthesis of fatty acids.

What enzyme is critical for transporting acetyl-CoA from the mitochondria to the cytoplasm for fatty acid synthesis?

• Citrate lyase

• Citrate synthase

• Malonyl-CoA reductase

• Acetyl-CoA carboxylase

• Lipase

Answer explanation

Citrate lyase catalyzes the cleavage of citrate back into oxaloacetate and acetyl-CoA in the cytoplasm, facilitating the transport of acetyl-CoA out of mitochondria.

The cytoplasmic biosynthesis of triglyceride and glycerophospholipid begins with ______ formation.

• Acetyl CoA

• Amino acids

• Fatty acids

• Cholesterol

• glycerol 3-phosphate

Answer explanation

The biosynthesis of triglycerides and glycerophospholipids begins with glycerol 3-phosphate, which acts as a backbone to which fatty acid molecules are attached through esterification.

Which molecule initiates the fatty acid synthesis process by reacting with acetyl-CoA to form malonyl-CoA?

• Glucose

• ATP

• Biotin

• NADPH

• CO2

Answer explanation

Malonyl-CoA is formed from acetyl-CoA and CO2, with the reaction catalyzed by acetyl-CoA carboxylase.

What does NADPH provide in the fatty acid synthesis process?

• Structural integrity

• Energy

• Reduction power

• Oxidation

• Transport

Answer explanation

NADPH provides the reducing equivalents needed for the reductive synthesis steps in fatty acid synthesis.

Which enzyme complex is responsible for most of the reactions in the fatty acid synthesis in mammals?

• Lipase

• Fatty Acid Synthase (FAS)

• Citrate synthase

• Glucose-6-phosphate dehydrogenase

• Pyruvate dehydrogenase

Answer explanation

Fatty Acid Synthase is a multifunctional enzyme complex that catalyzes the formation of long-chain fatty acids from acetyl-CoA and malonyl-CoA.

What is the role of malonyl-CoA in fatty acid synthesis?

• It is a direct source of energy.

• It acts as a transporter of lipids.

• It provides carbon units for chain elongation.

• It deactivates enzymes.

• It is a storage form of fatty acids.

Answer explanation

Malonyl-CoA is the molecule that donates two-carbon units to the growing fatty acid chain during synthesis.

What is the key intermediate substrate in the common pathway of the synthesis of triglycerides and glycerophospholipids?

• Fatty acids

• Glycerol 3-phosphate

• Acetyl CoA

• Cholesterol

• Phosphatidic acid

Answer explanation

The key intermediate substrate in the common pathway of the synthesis of triglycerides and glycerophospholipids is phosphatidic acid. Phosphatidic acid serves as a critical intermediate that can either be converted into diacylglycerol (DAG), which then leads to the synthesis of triglycerides, or it can be used to produce various types of glycerophospholipids through further reaction with CTP-derived substrates like CDP-choline or CDP-ethanolamine. This makes phosphatidic acid a central molecule in the biosynthesis of both triglycerides and phospholipids.

Which compound transports acetyl-CoA out of the mitochondria to the cytoplasm?

• Citrate

• Oxaloacetate

• Malate

• Pyruvate

• Lactate

Answer explanation

Citrate is formed in the mitochondria from acetyl-CoA and oxaloacetate and is transported to the cytoplasm where it is split by citrate lyase to release acetyl-CoA.