Exam 3

What is the biochemical explanation for why rapid weight loss is reported with protein-rich diets? A. Amino acid degradation results in urea production to remove excess NH4+, so mostly water weight loss. B. A protein-rich diet is a high energy regimen that leads to nervous energy and a strong desire to exercise. C. The rapid weight loss is due to ketogenesis and the "melting" of fat away from the thighs and upper body. D. Dieters usually over-estimate how much weight they actually lose on a diet and the data are likely flawed.

A. Amino acid degradation results in urea production to remove excess NH4+, so mostly water weight loss.

Phenylketonuria (1) / Albinism (2) is characterized by white skin due to a defect in the enzyme tyrosinase, which leads to a block in the pathway needed to synthesize adrenaline (3) / melanin (4). Animals with this condition have an increased risk of skin cancer (5) / mental illness (6). The genetic disease albinism (7) / phenylketonuria (8) is caused by a defect in the enzyme phenylalanine hydroxylase, which leads to the accumulation of tyrosine (9) / phenylalanine (10) derivatives that are toxic metabolites Choose the best underline word or phrase that correctly completes the sentence and record the numbers. A. 2, 4, 6, 8, 9 B. 2, 4, 5, 8, 10 C. 2, 3, 5, 7, 10 D. 1, 3, 6, 7, 9 E. 1, 4, 5, 7, 10

B. 2, 4, 5, 8, 10

Explain why glyphosate works faster in the summer after rain than after two weeks without rain. A. It does not work faster after it rains, it actually works less well because the glyphosate is oil based. B. It works faster after it rains because the plants rapidly use up phenylalanine, which becomes limiting in the presence of glyphosate. C. It works faster after it rains because the leaves are not wilted and the glyphosate spray sticks better. D. It works faster after it rains because the roots take up the glyphosate that is sprayed on the dirt.

B. It works faster after it rains because the plants rapidly use up phenylalanine, which becomes limiting in the presence of glyphosate.

Animals cannot synthesize tyrosine from shikimate-3P because they lack EPSP synthase. However, tyrosine is listed as a non-essential amino acid in most tables. What is the explanation? A. Tyrosine is not essential because it can be synthesized from tryptophan, and tryptophan is essential. B. Tyrosine can be synthesized from phenylalanine, and since phenylalanine is essential, tyrosine is not. C. Most animals do actually contain the enzyme EPSP synthase it is just not expressed all of the time. D. Tyrosine is essential until reaching puberty, and then after that, it is non-essential because of hormones. E. There are other pathways to synthesize tyrosine from shikimate-3P, so EPSP synthase is not required.

B. Tyrosine can be synthesized from phenylalanine, and since phenylalanine is essential, tyrosine is not.

Why is ingesting large amounts of L-arginine a viable treatment for argininosuccinase deficiency? A. Secreting fumarate would also work, but fumarate is an acid and it causes stomach bleeding. B. Citrulline can be excreted in the urine, which provides a way to remove excess dietary nitrogen. C. Arginine is converted to ornithine, which provides urea cycle intermediates needed for nitrogen removal. D. The aspartate-argininosuccinate shunt requires arginine to carry the nitrogen to the urea cycle. E. By ingesting large amounts of L-arginine, the patient is able to excrete large amounts of urea.

C. Arginine is converted to ornithine, which provides urea cycle intermediates needed for nitrogen removal.

Which one of the following amino acids is a starting material for the synthesis of heme? A. Histidine B. Alanine C. Glycine D. Phenylalanine E. Alanine

C. Glycine

Undiagnosed phenylketonuria (PKU) can lead to severe neuronal damage and mental incapacity, which is avoidable if the disease is diagnosed at birth. In contrast, albinism is easly diagnosed at birth, but there is no treatment, which leads to an increased risk of skin cancer in these patients. Choose the THREE statements that best explain the reasons for these differences. A. In developing countries the rate of phenylketonuria is much higher than in developed countries because of healthcare disparities. Albinism is found worldwide, even in animals. Therefore, the treatment options are different, which explains why albinos have high rates of skin cancer. B. Phenylketonuria is caused by insufficient tyrosine, which is why PKU individuals have light skin at birth. In contrast, albinism is cause by too many white pigments that accumulate when the enzyme tyrosinase is mutated. C. PKU is the result of substrate accumulation, which can be avoided using a restricted diet. However, albinism is due to a missing product, which cannot be replaced through injections or dietary regimens. D. It is easy to treat PKU because phenylalanine can be metabolized by other pathways to avoid neuronal damage, whereas albinos would need to eat excess tyrosine to produce pigments and not too many foods contain tyrosine. E. Phenylalanine is found in many types of food, including aspartame, and therefore by avoiding foods with high amounts of phenylalanine, the build-up pyruvate metabolites can be controlled. In contrast, skin pigments must be made from tyrosine and there is no way to do this if tyrosine metabolism is compromised. F. Defects in the enzyme tyrosinase occur in every cell of the body and there is no way to replace this enzyme without embryonic human gene therapy. In contrast, defects in the enzyme phenylalanine hydroxylase can be ameliorated by restricting certain amino acids in the diet. G. Albinism is not a disease it is a lifestyle choice, whereas PKU is recessive disease that protects people from skin cancer. H. PKU individuals can avoid the damaging effects of pyruvate metabolites by limiting the amount of Splenda in their food. In contrast, albinos cannot avoid sun exposure and eventually die of malignant melanoma.

C. PKU is the result of substrate accumulation, which can be avoided using a restricted diet. However, albinism is due to a missing product, which cannot be replaced through injections or dietary regimens. E. Phenylalanine is found in many types of food, including aspartame, and therefore by avoiding foods with high amounts of phenylalanine, the build-up pyruvate metabolites can be controlled. In contrast, skin pigments must be made from tyrosine and there is no way to do this if tyrosine metabolism is compromised. F. Defects in the enzyme tyrosinase occur in every cell of the body and there is no way to replace this enzyme without embryonic human gene therapy. In contrast, defects in the enzyme phenylalanine hydroxylase can be ameliorated by restricting certain amino acids in the diet.

A person who has alkaptonuria is easily diagnosed from the presence of black urine. What causes the black color? A. dehydration B. reduction of homogentisate C. oxidation of homogentisate D. oxidation of phenylalanine E. reduction of acetoacetyl-CoA

C. oxidation of homogentisate

Why does it make sense that tadpoles (which live in water) have low levels of the enzyme arginase, but after metamorphosis into frogs (which live on land), their arginase levels increase? A. The volume of water in a pond is so large that tadpoles can excrete ammonia directly and not die. B. Frogs are able to walk around and excrete urea in lots of places, but tadpoles are confined to a pond. C. Tadpoles develop into frogs when ammonia levels in the pond gets too high and they crawl on land. D. Tadpoles living in water can excrete ammonia directly, but once on land, they need to excrete urea. E. Arginase is the enzyme that converts glutamine to glutamate and therefore required for urea cycle.

D. Tadpoles living in water can excrete ammonia directly, but once on land, they need to excrete urea.

Why do angina patients carry nitroglycerine with them? A. to increase heart rate during a heart attack. B. to inhibit acetylcholine release from neurons C. to inhibit cGMP phosphodiesterase D. as a rapid source of NO for blood vessel dilation E. as a source of ammonia for muscle relaxation

D. as a rapid source of NO for blood vessel dilation