Amino Acid and Protein Metabolism-II

Which of the following amino acids is NOT considered essential for dogs according to the presentation?

• Lysine

• Methionine

• Valine

• Arginine

• Glycine

Answer explanation

Glycine is not listed as an essential amino acid for dogs in the presentation. Essential amino acids are those that cannot be synthesized by the animal's body and must be obtained from the diet.

Which amino acid family includes amino acids synthesized by transamination of oxaloacetic acid?

• Pyruvic Acid Family

• Aspartic Acid Family

• Shikimic Acid Family

• Uric Acid Family

• Lactic Acid Family

Answer explanation

The Aspartic acid family includes amino acids like lysine, methionine, threonine, and isoleucine, which can be synthesized by transamination of oxaloacetic acid. These amino acids are not synthesized by human and its monogastric livestock and should be supplemented in their diets. Among the Asp-family amino acids, Lys is considered as the nutritionally most important essential amino acid because its level is most limiting in cereal grains, representing the largest source of plant foods and feeds worldwide.

What is the metabolic importance of transamination reactions involving glutamate and aspartate?

• They are primary processes in lipid synthesis.

• They facilitate the elimination of ammonia.

• They play a central role in nitrogen metabolism.

• They convert fatty acids into acetyl-CoA.

• They are not significant in metabolism.

Answer explanation

Transamination reactions, involving amino acids like glutamate and aspartate, are crucial for transferring nitrogen within the body, linking it to the metabolism of amino groups and ultimately the urea cycle.

What is the primary role of urea synthesis in mammals?

• To break down fatty acids

• To synthesize amino acids

• To convert ammonia to a non-toxic compound

• To promote digestion of proteins

• To enhance lipid metabolism

Answer explanation

The primary role of urea synthesis in mammals is to detoxify ammonia, which is toxic, by converting it into urea, which can be safely excreted through the kidneys.

Which enzyme is not involved in urea cycle?

• Asparaginase

• Arginase

• Carbamoyl phosphate synthase

• Ornithine carbamoltransferase

• Argininosuccinate lyase

Answer explanation

Asparaginase catalyzes the hydrolytic cleavage of asparagine to aspartic acid, releasing ammonia in the process. Asparaginase is an enzyme that is used as a medication and in food manufacturing. As a medication, L-asparaginase is used to treat acute lymphoblastic leukemia (ALL) and lymphoblastic lymphoma (LBL). It is given by injection into a vein, muscle, or under the skin. A pegylated version is also available. In food manufacturing it is used to decrease acrylamide. Besides Carbamoyl phosphate synthase is also incorrect. It must be synthetase because the reaction it catalyse requires ATP or it's an ATP driven reaction.

In which organ is ammonia primarily converted into urea?

• Kidney

• Liver

• Intestine

• Cardiac tissue

• Pancreas

Answer explanation

The liver is the primary site for urea synthesis, where ammonia is converted into urea to reduce toxicity and facilitate safe excretion.

Which of the following reactions is the first and rate-limiting step of the urea cycle?

• Citrulline formation

• Argininosuccinate formation

• Cleavage of argininosuccinate

• Formation of carbamoyl phosphate

• Urea formation

Answer explanation

The formation of carbamoyl phosphate, catalyzed by carbamoyl phosphate synthetase-1 (CPS-1), is the first and rate-limiting step of the urea cycle. Ammonia is the source of the first amine group of urea.

What is the primary role of alpha-ketoglutarate in amino acid metabolism?

• It serves as the primary nitrogen donor in the urea cycle.

• It converts directly to glucose via gluconeogenesis.

• It is a direct precursor for the synthesis of urea.

• It acts primarily as a ketone body.

• It is a critical intermediate in the TCA cycle and serves as an amino group acceptor in transamination reactions.

Answer explanation

Alpha-ketoglutarate plays a crucial role in amino acid metabolism as an intermediate in the TCA cycle and as an amino group acceptor in transamination reactions to form glutamate.

Which of the following best describes the primary nitrogen waste products excreted by ureotelic, ammonotelic, and uricotelic organisms, respectively?

• Uric acid, urea, and ammonia

• Ammonia, uric acid, and urea

• Urea, ammonia, and uric acid

• Urea, uric acid, and ammonia

• Ammonia, urea, and uric acid

Answer explanation

• Ureotelic organisms (like most mammals) excrete nitrogen primarily as urea, which is less toxic and conserves water.

• Ammonotelic organisms (like many aquatic animals) excrete ammonia directly into their environment because it can be diluted by the surrounding water.

• Uricotelic organisms (like birds and some reptiles) excrete uric acid, which is less soluble in water and conserves more water compared to urea, making it advantageous in arid environments.

In cats, a deficiency in which essential amino acid could lead to issues with ammonia metabolism and subsequent symptoms of hyperammonemia?

• Arginine

• Leucine

• Lysine

• Methionine

• Tryptophan

Answer explanation

Arginine is crucial in the urea cycle for cats. A deficiency in arginine can disrupt the urea cycle, leading to the accumulation of ammonia in the bloodstream (hyperammonemia). This condition can result in severe neurological disorders and, if not treated, can be fatal. Cats, unlike some other animals, cannot synthesize arginine and must obtain it directly from their diet. Research has shown that cats fed a diet specifically formulated to be deficient in arginine exhibit signs of ammonia toxicity which include drooling, vomiting, lethargy and even convulsions within hours of consuming the diet.