Lipid Metabolism Biochemistry MCQ Quiz With Answers

Proteins are not lipids. Lipids are a class of biomolecules that include oils, fats, and waxes. They are characterized by their hydrophobic nature and are important for energy storage, insulation, and protection. Proteins, on the other hand, are macromolecules composed of amino acids and have various functions in the body, such as enzyme catalysis, structural support, and transportation. While lipids are primarily composed of carbon, hydrogen, and oxygen, proteins contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. Therefore, proteins do not fit the definition of lipids and are not considered as such.

The liver and intestines are the most active organs in the animal body that can synthesize triacylglycerol. Triacylglycerol is a type of fat that is synthesized in the liver and intestines through a process called lipogenesis. The liver plays a crucial role in lipid metabolism and is responsible for synthesizing and storing triacylglycerol. The intestines also contribute to the synthesis of triacylglycerol by absorbing dietary fats and converting them into triacylglycerol for storage or energy production. Therefore, the correct answer is liver and intestines.

Acetyl CoA is the precursor for fatty acid synthesis. Fatty acid synthesis occurs in the cytoplasm of cells and requires Acetyl CoA as the starting molecule. Acetyl CoA is formed from the breakdown of glucose or from the oxidation of fatty acids. It is then converted into malonyl CoA, which is used in the synthesis of fatty acids. Therefore, Acetyl CoA is the correct answer as it is the initial molecule in the pathway of fatty acid synthesis.

Fatty acid β-oxidation is a process that occurs in the mitochondria. This is where fatty acids are broken down into acetyl-CoA molecules, which can then enter the citric acid cycle to produce energy. Peroxisomes and lysosomes are involved in other cellular processes, but they do not play a direct role in fatty acid β-oxidation. Therefore, the correct answer is mitochondria.

Phosphorylation is the process of adding a phosphate group to a molecule, which often leads to a change in its activity or function. In the case of acetyl CoA carboxylase, phosphorylation inactivates the enzyme. Acetyl CoA carboxylase is an important enzyme involved in fatty acid synthesis, and its inactivation through phosphorylation helps regulate the production of fatty acids in the cell.

Acetyl CoA cannot directly diffuse from the mitochondrial membrane into the cytosol. Instead, it is converted into citrate within the mitochondria by the enzyme citrate synthase. Citrate is then transported across the mitochondrial membrane into the cytosol, where it is converted back into acetyl CoA by the enzyme ATP-citrate lyase. This allows for the regeneration of acetyl CoA in the cytosol, which is necessary for the synthesis of fatty acids.

De novo fatty acid synthesis occurs in the cytosol. This is where the enzymes responsible for the synthesis of fatty acids are located. The process involves the conversion of acetyl-CoA into long-chain fatty acids, which are then used for various cellular functions such as energy storage or membrane synthesis. The cytosol provides a suitable environment for these enzymatic reactions to take place efficiently.

Acetyl CoA carboxylase is the enzyme that catalyzes the conversion of acetyl CoA to malonyl CoA, which is the rate limiting step in fatty acid synthesis. This enzyme adds a carboxyl group to acetyl CoA, resulting in the formation of malonyl CoA. This step is important in controlling the overall rate of fatty acid synthesis, as it determines the availability of malonyl CoA, which is a key precursor for fatty acid production.

Free fatty acids in the plasma bind to albumin and circulate. Albumin is a protein found in the blood that acts as a carrier for various substances, including fatty acids. When fatty acids are released from adipose tissue or dietary intake, they bind to albumin for transport to various tissues in the body. This binding helps to prevent the fatty acids from being rapidly metabolized or excreted, ensuring their delivery to cells where they can be utilized for energy or stored as fat.

Citrate is the correct answer because it acts as an allosteric regulator of acetyl CoA carboxylase. Acetyl CoA carboxylase is an enzyme involved in fatty acid synthesis, and citrate acts as a positive regulator, activating the enzyme. When citrate levels are high, it indicates an abundance of metabolic intermediates, suggesting that the cell has sufficient energy and resources for fatty acid synthesis. Therefore, citrate binding to acetyl CoA carboxylase promotes the production of fatty acids.