Exam 3

Its good to be king -healthy 25 yr. old male-->has acute sharp and stabbing abdominal pain -wife reports he is sometimes anxious and fidgety for no reason -some times abdominal pain leads to vomiting (can be bloody) -Dr. found no evidence of infection (confirmed by blood test) -ER admitted w/ BP 180/120 but CT scan negative -parents immigrated from Romania, in a region near Carpathian range -What is the diagnosis, biochemical mechanism and primary effect?

-ACUTE INTERMITTENT PORPHYRIA --defect in the porphobilinogen deaminase causing decreased heme and accumulation of porphobilinogen; symptoms are triggered by hormons, drugs and diet -gene--> environment

The brain requires a constant input of glucose. The metabolic activity of which organ(s) is/are necessary to maintain the concentration of glucose required by the brain when dietary glucose is low?

-Adipose tissue -Kidney -Liver

Squidward Q. Tentacles -Chip was homeschooled K-12 and then went to college -Although he lived a sheltered life, he enjoyed the idea of meeting new people -First night he got drunk and urinated in the swimming pool -people cleared the pool when a cloud of blackish water surrounded Chip -Chip was surprised that people outside his family have yellow urine -Chips frat nicknamed him Squidward for a very good reason What is the diagnosis, biochemical mechanism?

-Alkaptonuria -Deficiency in the enzyme homogentisate 1,2-dioxygenase

Patients with type 1 diabetes must inject insulin up to several times a day and monitor their carbohydrate intake to regulate their blood glucose level. The amount of insulin injected is based on the carbohydrate content of the diet and so must be adjusted accordingly; otherwise, hypoglycemia will result. What explains why injecting too much insulin before a meal results in hypoglycemia?

-Increased glycogen storage -Decreased glucose synthesis -Increased glucose uptake

How does depletion of liver glycogen stores during starvation lead to a shift from glucose utilization to fatty acid oxidation as an energy source for most tissues?

-Lack of liver glycogen stores results in a drop in serum glucose concentration. -Lack of insulin signaling reduces GLUT4 translocation. -Glucagon activates hormone-sensitive lipase.

Glycogen can provide fuel for both a short race (e.g., 200 m) and a long race (i.e., 10 K or more). What best describes the use of muscle and liver glycogen during short and long races?

-Liver glycogen can be used to fuel long runs. -Muscle glycogen can be used to fuel short runs. -Muscle glycogen can be used to fuel long runs.

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.

-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. -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 -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.

What is the difference between the synthesis of Purines and Pyrimidines? What is an example of each?

-Purine bases are synthesized directly on the ribose sugar, whereas pyrimidine bases are first synthesized as a closed ring before attaching to the ribose sugar. -Purines: Adenine, Guanine -Pyrimidines: Cytosine, Thymine, Uracil (RNA)

Bah Hum bug - volunteer w/ flying Samaritans brings sm. boy to physician -boys body is hunched over and he can barely walk on his own -boys wrists and ankles are thickened and enlarged -patients abdomen is distended and breastbone protruding -boy's height is in 30th percentile for age -villages live in a large cave during the day to avoid the hot sun -What is the diagnosis, biochemical mechanism and primary effect?

-Rickets Disease -Rickets is in remote areas (not in US) -abdomin distended (undernourished- no Vitamin D, doesn't have to do with disease really -live in cave--> NO SUN! -Rickets is caused by a deficiency of Vitamin D, which results in reduced bone growth due to increased expression of vitamin D receptor regulated genes -ligand is Vitamin D -Vitamin D is activator of transcription factor environment -b/c if you just get Vitamin D, you will be fine!

In the reaction mechanism of the E. coli ribonucleotide reductase, which state does the cysteine side chain never exist in?

-SOH

How does the cell regulate the substrate specificity of ribonucleotide reductase to maintain equal amounts of all four deoxynucleoside triphosphates (dNTPs)?

-When dTTP is bound to the specificity site, more dGDP is produced. -When dGTP is bound to the specificity site, more dADP is produced.

Which of the nucleotides is/are synthesized from a pathway that involves inosine-5'-monophosphate?

-guanosine monophosphate -adenosine monophosphate

What cellular change(s) would not encourage the Krebs bicycle and thus the probability of the urea cycle taking place to completion?

-increased conversion of oxaloacetate into citrate -increased aspartate charging to mitochondrial tRNAs

From Russia needs love -female, 6 from russia (blue eyes, blonde hair) -mental deficiencies, functions at level of a 18month old -Guthrie test positive, urinary prterin analysis normal -normal diet -weird body odor -no family history What is the diagnosis, biochemical mechanism and primary effect?

-phenylketonuria -PKU is generally seen in family members -phenylalanine hydroxylase deficiency, leads to a build up of neurotoxic phenylalanine derivatives -genes-->environment -if you don't eat phenylalanine, you won't have a problem

What cellular condition(s) would cause the up-regulation of AMPK activity?

-phosphorylation of Thr172 in the α subunit -low energy charge in muscle cells

More Gin, Less tonic-please - young woman gets sulfadiazine treatment for urinary infection -after 3 wks of antibiotics, lethargic but no infection -getting leg cramps and demeanor is irritable -epidermis and sclera appear yellow and urine is brown tint - blood test shows low levels of erythrocytes, high levels bilirubin -father born in kenya and mothers grandparents from italy -What is the diagnosis, biochemical mechanism and primary effect?

-primaquine-induced anemia (G6PD deficiency) -sulfadiazine--> compound that induced problem --G-6P dehydrogenase deficiency results in low NADPH, which decreases the amount of reduced glutathione needed to detoxify ingested oxidants -genes-->environment effect

Inhibition of what processes would disrupt the regulation of metabolic homeostasis?

-somatostatin release from the pancreas -glucagon release from the pancreas -PPAR nuclear receptor activation -insulin release from the pancreas

What are the four major changes in metabolic flux under starvation conditions?

1.Increased triacylglycerol hydrolysis in adipose tissue 2.Increased gluconeogenesis in kidney and liver cells 3.Increased ketogenesis in liver cells 4.Protein degradation in skeletal muscle cells

A man who does not have Lesch-Nyhan syndrome and a woman whose mother and father both had Lesch-Nyhan syndrome have a male child together. What are the chances that this child will have Lesch-Nyhan syndrome? Assume a traditional Mendelian X-linked recessive inheritance pattern for the purpose of this question and assume that all organisms are fertile.

100%

Why are cancer patients given high doses of 5-fluorouracil?

80% of this compound is metabolized by normal dihydropyrimidine dehydrogenase activity.

Explain the difference between a gene effect and an environment-->gene effect in regards to human disease

A gene effect is one that is encoded in the genome at birth (ex: albinism). A environment-->gene effect has to do with a change in the genome as a result of an environmental factor, such as radiation.

What sequences of enzymatic activity would produce one of the nucleotides that is used as a substrate by a polymerase?

A guanylate kinase reaction, then a ribonucleotide reductase reaction, and finally a nucleoside diphosphate kinase reaction.

According to the thrifty gene hypothesis, what gene varients could be candidate thrifty genes whose expression would increase the chances that an individual would develop insulin resistance?

AMPK with a lower affinity for AMP

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

Albinism melanin cancer phenylketonuria phenylalanine

What is the biochemical explanation for why rapid weight loss is reported with protein-rich diets?

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

Upon deamination of an amino acid, which component becomes substrate for the urea cycle?

Ammonia

How does a defect in adenosine deaminase (ADA) lead to inhibition of DNA synthesis?

An ADA deficiency increases dATP levels, which inhibits ribonucleotide reductase and DNA synthesis.

An increase in SAICAR lyase activity would most directly cause which of the following?

An increase in the production of malate by way of the citrate cycle

Nitric oxide (NO) is a potent vasodilator in humans. Synthesis of NO occurs by a two-step enzymatic reaction that is catalyzed by nitric oxide synthase. Which amino acid(s) can serve as substrate for this enzyme?

Arginine

Why is ingesting large amounts of L-arginine a viable treatment for argininosuccinase deficiency?

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

What is a substrate of the urea cycle?

Aspartate

Which amino acid provides the majority of carbons in the pyrimidine ring system?

Aspartate

How many rounds of ubiquitination must a condemned protein undergo to facilitate proteasomal recognition?

At least 3 times is sufficient

What does not occur during starvation

Brain cells begin using fatty acids as an energy source.

What statements is true regarding the regulation of pyrimidine biosynthesis in animal cells?

CTP negatively regulates CTP synthase, and therefore CTP negatively regulates its own biosynthesis.

What statements is true regarding the regulation of pyrimidine biosynthesis in E. coli?

CTP negatively regulates carbamoyl aspartate synthesis.

What is FALSE concerning dihydropyrimidine dehydrogenase?

Cancer patients with dihydropyrimidine dehydrogenase deficiencies do not face tissue toxicity when treated with standard amount of 5-fluorouracil.

Explain how a deficiency in the enzyme dihydropyrimidine dehydrogenase (DPD) could lead to severe side effects in cancer treatments using 5-fluorouracil (5-FU) as a chemotherapeutic agent.

DPD degrades 5-FU so high doses need to be given, if DPD is deficient, then high 5-FU doses are toxic.

What catecholamine is made by the action of tyrosine hydroxylase and aromatic amino acid decarboxylase? (Assume that a biologically relevant molarity of all substrates for both tyrosine hydroxylase and aromatic amino acid decarboxylase are available.)

Dopamine

Why was gout associated with ethanol and meat consumption?

Ethanol interferes with excretion of purine breakdown chemicals and some foods contain high levels of purines.

How does ephedrine work to stimulate weight loss?

Fatty acid oxidation is increased

How is flux through the purine biosynthetic pathway regulated

Flux through the purine biosynthetic pathway is primarily controlled by inhibition of the PRPP synthetase and glutamine-PRPP amidotransferase reactions.

In the Krebs bicycle, what citrate cycle intermediates links to the urea cycle via argininosuccinate?

Fumarate

What is false concerning the effects of insulin and glucagon?

Glucagon stimulates glucose export in skeletal muscle.

Insulin signals for an increase in glucose uptake in both skeletal muscle and adipose tissue. What correctly describes how these organs use this glucose?

Glucose in muscle cells is completely oxidized or stored as glycogen, depending on the ATP demand. In adipose tissue, glucose is used to synthesize fatty acids and glycerol.

What statements correctly describes an interaction between the ATP and GTP biosynthetic pathways?

Greater ATP production will positively regulate GTP synthesis because ATP is involved in the conversion of xanthosine-5'-monophosphate into guanosine-5'-monophosphate.

What amino acid is NOT produced from the shikimate pathway product chorismate?

Histidine

What best defines nitrogen balance?

Human daily intake of nitrogen, primarily in the form of protein, equals the amount of nitrogen lost by excretion in the feces and urine.

Individuals who develop type 2 diabetes are often overweight or obese (i.e., exhibit hyperlipidemia), although there is no correlation between weight and the development of type 1 diabetes. Why does obesity contribute to the development of type 2 diabetes?

Hyperlipidemia reduces adiponectin release from adipose tissue.

Gout is due to a build up of uric acid crystals which can be due to either excess production of uric acid by the purine biosynthetic pathway, or inability to excrete uric acid leading to build up Considering that uric acid is derived from both purine biosynthesis and by die, explain how feeding a patient 15N-glycine and measuring the amount of 15N in excreted urine can distinguish between these two causes of gout?

If there is 15N in the urine that most likely a result of excess production of uric acid since 15N-glycine will incorporate 15N into purines and then uric acid that is excreted because in excess (cause of the gout). If however, there is very little 15N in the urine, then likely inability to break down or excrete uric acid since most of the uric acid normally comes from the diet and it would not therefore be 15N labeled.

Why do individuals with both type 1 and type 2 diabetes have elevated blood glucose levels but respond differently to the same dose of injected insulin?

Individuals with type 1 diabetics are insulin deficient, but the intracellular insulin signaling pathways are inhibited in individuals with type 2 diabetes.

Pancreatic β cells release insulin from intracellular vesicles. This release is regulated in part by the activity of glucokinase. How would insulin release be affected if pancreatic β cells were mutated to express hexokinase rather than glucokinase?

Insulin release from pancreatic β cells would be constant if hexokinase was expressed rather than glucokinase, and expression of insulin would not be affected by changes in the serum glucose.

What best explains why nucleotide salvage pathways evolved?

It is energetically expensive for the cell to solely rely on de novo biosynthetic pathways.

Insulin stimulates glucose uptake and fatty acid synthesis. With this in min, why is it a bad idea to eat 3 milky way chocolates before a 60 mile bike race to get energy for this 3 hour event?

Lead to a very prominent release of insulin and quickly uses up glucose which leads to a crash and lack of glucose

Individuals wishing to lose weight are often advised to eat foods with a low glycemic index (GI). How could glycemic index affect weight loss?

Low GI foods can decrease the rate of fatty acid synthesis

What provides the methyl group for conversion of dUMP to dTMP?

N5,N10-methylenetetrahydrofolate

Terri and Ronise are both runners. Terri is a short-distance runner for the university track team and competes primarily in 100-meter and 200-meter sprints. Ronise competes in local 10K races and has even completed a half-marathon. Terri notices that Ronise brings glucose gels with her on her longer training runs. Terri asks Ronise if the glucose gels could give her a boost if she ate one halfway through her 200-meter sprint. What should Ronise tell her?

No, ingesting a glucose gel during a 200-meter sprint will not provide useful fuel, and may even decrease the efficiency of ATP synthesis.

Would 5-fluorouracil be suitable for a patient that has demonstrated dihydropyrimidine dehydrogenase hyperactivity?

No, the drug would probably not remain at high enough molarity to be bioactive.

What are three mechanisms by which cancer cells become resistant to the drug methotrexate?

Overexpression of drug transporter, DHFR mutation blocking drug binding, DHFR gene amplification

AMPK activation during short periods of intense exercise can promote ATP synthesis from glucose. What AMPK activities explains why this can occur?

Phosphorylation of glycogen synthase and phosphofructokinase-2

What is NOT involved in the feedback regulation of purine biosynthesis?

Pi

What enzyme is stimulated by insulin in liver cells only

Protein Phosphatase 2A

Nucleotide salvage pathways most commonly act upon

RNA

What is correct concerning ribonucleotide reductase?

Ribonucleotide reductase in most eukaryotes contains a dinuclear Fe3+ center in the R2 subunit.

Describe the biochemistry behind RoundUp Ready crops, i.e., what is a RoundUp Ready plant, why does it yield more crop per acre, and what are the potential problems with such a strategy with regard to overuse of glyphosate?

RoundUp Ready crops are resistant to the herbicide RoundUp (glyphosate) because they carry a bacterial gene encoding a variant of the enzyme EPSP synthase, a required enzyme in amino acid biosynthesis. RoundUp Ready crops can be sprayed with the herbicide and survive, but encroaching weeds will die, thus leading to higher crop yields. Some data suggest that excessive use of glyphosate could be harmful to animals, and moreover, glyphosate-resistant native plants will emerge

Elevated levels of free fatty acids and elevated levels of TNF-α can both result in a decrease in sensitivity to insulin. What do the mechanisms of both have in common?

Serine phosphorylation on the insulin receptor substrate protein

More ATP per carbon is produced from oxidation of fatty acids as compared to glucose. However, fatty acids are used primarily to provide fuel for ATP synthesis during long periods of exercise. Why can't fatty acids be used to fuel short, intense periods of exercise?

Short, intense periods of exercise do not provide sufficient time for oxidative phosphorylation to occur.

How does regulation of metabolic homeostasis by insulin and glucagon signalling differ from regulation by activation of peroxisome proliferator-activated receptor (PPAR) nuclear receptors?

Signalling mediated by activation of PPAR nuclear recpetor proteins is initiated in response to different metabolic signals than insulin and glucagon signalling.

Why can't muscle cells export or store excess glucose as adipose tissue?

Skeletal muscle lacks glucose 6 phosphatase which is typically used by the liver to turn G6P to glucose and export it. In addition, Muscle cells also don't have fatty acid synthase

Many popular diets exist, each with a different "eating plan" designed to promote weight loss. Common diets include the Atkins diet, Weight Watchers, the Zone diet, and the Ornish diet. Although these diets can be effective, there does not appear to be an advantage to any particular diet. In addition, many individuals do not lose weight when following these diets. What could be a reason that weight loss does not occur when someone follows one of these fad diets?

Strict adherance to the eating plan is required for significant weight loss to occur.

Defects in nucleotide metabolism that lead to a buildup of uric acid cause the disease gout. What is true about this?

Supplying humans with the enzyme urate oxidase theoretically could be effective in reducing uric acid levels. An inhibitor of xanthine oxidase, such as allopurinol, will limit the conversion of hypoxanthine to uric acid, and could be effective in reducing uric acid levels.

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?

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

How is the balance of AMP and GMP regulated?

The balance of AMP and GMP synthesis is controlled by both feedback inhibition of the individual branches in the pathway and by ATP and GTP cross-talk regulation

Considering the physiology of thymidylate synthase, why is Tomudex an effective anticancer drug?

The drug is a noncompetitive inhibitor that binds to thymidylate synthase and decreases enzymatic activity. This causes an imbalance in the quantities of dNTPs that are available for DNA replication.

Explain how an enzyme deficiency in dihydropyrimidine dehydrogenase could lead to severe side effects in a cancer treatment regimen using 5-fluorouracil; what would be the alternative treatment?

The enzyme dihydropyrimidine dehydrogenase (DPD) modifies 5-fluorouracil (5-FU), which leads to its degradation and inactivation as a cancer drug inhibiting DNA synthesis. Because of this, high doses of 5-FU must be given to reach an effective dose in the patient (80% is degraded). However, in patients with a DPD deficiency, these high doses of 5-FU can be very toxic because most is not degraded. The alternative treatment in patients with DPD deficiency is to lower the dose of 5-FU.

What is the first reaction in the purine degradation catalyzed by?

The rate-limiting enzyme dihydropyrimidine dehydrogenase, which converts uracil and thymine to dihydrouracil and dihydrothymine, respectively

Insulin-stimulated glucose uptake and utilization by skeletal muscle and liver cells results in a reduction in the blood glucose level. Which organ is primarily responsible for the decrease in serum glucose, and why?

The skeletal muscle is responsible for the majority of glucose uptake, as the total mass of skeletal muscle is greater than the mass of liver cells

Uracil is not found in DNA, so why does it make sense that ribonucleotide reductase converts UDP to dUDP

The substrate for thymidylate synthase is dUMP, which is derived from dUDP

After covalent modification of a target protein with the ubiquitin that is shown in the molecular structure, what is the most likely fate of the ubiquitin chain?

The target protein, without the polyubiquitin attachment, will be accepted into the proteasome and digested; ATP will be consumed during this process. The ubiquitin concentration in the cytoplasm will remain stable.

What is correct and most accurately describes the complete urea cycle of the eukaryotic cell?

The urea cycle occurs between the mitochondrial matrix and the cytoplasm of the eukaryotic cell.

What amino acid is the precursor of catecholamines?

Tyrosine

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?

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

What pathway does NOT provide metabolic precursors for amino acid synthesis?

Urea

What is a common breakdown product between AMP and GMP degradation to uric acid?

Xanthine

Do PPARα-specific agonists theoretically offer more advantages for lowering cholesterol as compared to traditional statin drugs?

Yes, treatment with PPARα-specific agonists affects cholesterol transport and uptake as well as synthesis, whereas statins affect synthesis only.

Nitrogen atoms that are removed from proteins during protein catabolism are least likely to be conserved in the structure what?

acetyl-CoA

Endothelial cells can receive a chemical signal from neurons. This signal is in the form of neuronal (A) _______ release. This chemical messenger binds to a membrane receptor that engages a signal transduction pathway, which increases the cytoplasmic concentration of (B) _____ ions. This ionic secondary messenger then activates endothelial nitric oxide synthase.

acetylcholine, calcium

What is an autosomal recessive disease caused by mutations in the gene encoding tyrosinase?

albinism

The onset of __________ is due to a recessive mutation in the gene encoding homogentisate-1,2-dioxygenase, an enzyme in the phenylalanine and tyrosine degradation pathways.

alkaptonuria

Which enzyme class best describes the activity of a urease?

amidohyrolase

Why do angina patients carry nitroglycerine with them?

as a rapid source of NO for blood vessel dilation

To determine the role of glutaredoxin in the generation of deoxyribonucleotides by ribonucleotide reductase, which organisms would be the best to study?

bacteria

What is a product of uracil degradation?

beta-alanine

During heme catabolism, which enzyme participates in heme breakdown while also serving an NADPH oxidase role in the reaction?

biliverdin reductase

What combinations accurately represents the final products of the two-step nitric oxide synthase reaction?

citrulline, nitric oxide, and water

There are many diseases collectively called porphyrias that are characterized by the accumulation of heme precursors in the blood and liver. Which type of porphyria is characterized by low uroporphyrinogen III synthesis?

congenital erythropoietic porphyria

Within the proteasome, the protease catalytic sites are located within

core particle only

Binding of __________ to the active site of ribonucleotide reductase inhibits all activity.

dATP

Carbamoyl phosphate and aspartate are substrates of aspartate transcarbamoylase. Aspartate transcarbamoylase synthesizes a product that becomes substrate for which enzyme?

dihydroorotase

A purinosome, a multi-enzyme complex, is part of purine biosynthesis in what?

eukaryotes only

Carbon skeletons from proteins during protein catabolism can be readily conserved in the structure of what?

fatty acids, glucose, and ketone bodies

If a mutation of the decarboxylase enzyme that functions in the biosynthetic pathway of UMP caused the pathway to halt at that step, what would no longer occur?

generation of CO2

What is a starting material for the synthesis of heme?

glycine

In Lesch-Nyhan syndrome patients, which enzyme is not functional?

hypoxanthine-guanine phosphoribosyltransferase

The bioactive 5-fluorouracil ______ a six-atom heterocyclic ring.

is

A condemned protein is covalently modified by ubiquitin at _______ residues.

lysine

When observing both ubiquitin polypeptides in this molecular structure that are covalently bonded together, the covalent bond that leads to polyubiquitination is a bond between which two residues?

lysine and glycine

Within the urea cycle, citrulline is produced by ornithine transcarbamylase in the ________and is consumed in the _________

mitochondria cytoplasm

In a eukaryotic cell, deamination of amino acids takes place most extensively in the

mitochondrial matrix

During IMP biosynthesis, fumarate is released as a byproduct. Fumarate is cleaved from a(n) atom on the developing heterocyclic ring of the purine.

nitrogen

What is the composition of the eukaryotic proteasome?

one 20S core particle and two 19S regulatory particles

Reducing power from which of the following would help drive the nitric oxide synthase reaction?

pentose phosphate pathway

Consider a cell that is using protein as a primary carbon/energy source. What amino acids would be most relevant for this cell in terms of glycogen synthesis?

serine

The stage of purine biosynthesis that ends with 5-aminoimidazole ribonucleotide synthesis is responsible for building

the imidazole ring of the purine base

Five nucleotide bases are found in nucleic acids. Name a pyrimidine/purine in that order

thymidine/adenine

Only __________ can be synthesized in plants, fungi, and bacteria by the shikimate pathway.

tryptophan, tyrosine, and phenylalanine

In the proposed mechanism for the E. coli ribonucleotide reductase reaction, a ____ radical in the R2 subunit is reduced by Cys439 in the R1 subunit.

tyrosine

What is NOT a fate of the carbon atoms from amino acid catabolism?

urea cycle

What purine metabolite is the likely cause of gout?

uric acid

Which of the following is a common breakdown product between AMP and GMP degradation to uric acid?

xanthine

In humans, allopurinol can be used as treatment for gout because this drug is a competitive inhibitor of

xanthine oxidase

The complete deactivation of what would destroy the ability of a cell to generate uric acid?

xanthine oxidase