Chapter 18 Amino acid Oxidation and the Production of Urea

What are four amino acids that be converted directly (in one step ) into pyruvate or a citric acid cycle intermediate , and name the intermediate formed from each.

-Aspartate , oxaloacetate -glutamate, alpha-ketoglutarate -alanine, pyruvate -serine, pyruvate

Fill in the blank : Transamination reactions are catalyzed by a family of enzymes , all of which require __________as a coenzyme. In the first step of transamination the coenzyme in the aldehyde form condenses with the ____________ group of an amino acid to form a __________

-Pyridoxal phosphate (PLP) -alpha amino group -Schiff base (external aldimine or imine)

Which fo the following conversions require more than one step to be produced ? 1. Alanine >>>>Pyruvate 2.Aspartate>>>>oxaloacetate 3.Glutamate>>>> alpha-ketoglutartae 4.Pheynlalanine >>>> hydroxyphenylpyruyvate 5. Proline >>>> glutamte

4 and 5

Suppose you are responsible for formulating the diet for a 4 year old boy with phenylketonuria . How do you decide what kind and amount fo protein to include in the diet?

A growing 4 year old boy would still need the phenylalanine and tyrosine for the synthesis of new proteins . Yet, excess amount of phenylalanine and tyrosine is toxic for phenylketonuries . Therefore, the diet should include just enough of these amino acids in proteins to supply the body , but not enough so that phenylketones begin to accumulate in the blood and urine . If the defect lies in the enzyme that regenerates tetrahydrobiopterin , then 1-3 ,4 -dihydroxyphenylalalnine and 5-hydrotryptophan must be supplied in the diet . Adding tetrahjydrobiopterin to the diet will not help because the compound is unstable and cannot cross the blood -brain barrier

Define zymogen and describes the role of one zymogen in protein digestion?

A zymogen is an inactive form of enzyme that be activated by proteolytic cleavage . The pancreatic enzyme pepsinogen , chymotrypsinogen , trypsinogen , and procaboxypepetidases Aand B are all inactive form of protease, which are active by proteolytic cleavage ager the release into the small intestine.

Describe the three general mechanism for disposing of excess nitrogen obtained int he diet. Which organism use each mechanism?

Ammonotelic animals = excrete NH4+ , and are usually aquatic vertebrates and larvae of amphibia Ureotelic animals = excrete urea , and are terrestrial vertebrates and sharks Uricotelic animals = excrete uric acid and are usually birds and reptiles

What amino acid directly donates the second nitrogen atom during the formation of urea in the urea cycle.?

Aspartate

What are the the alpha-keto acids resulting from the following amino acids when reacting with alpha-ketoglutartate : 1. Aspartate 2. Alanine

Aspartate>>>> Oxaloacetate Alainine>>>> Pyruvate

Which statement is TRUE regarding lysine ? A)this is a nonessential amino acid B)Catabolis of lysine shares multiple steps with that of tryptophan C)Carbons of lysine catabolism enter the citric acid cycle succinylcholine-CoA D)Lysine is both glycogenic and ketogenic enzyme

Catabolism of lysine shares multiple steps with that of tryptophan

In which pair of compounds is the second molecule produced by the deamination of the first molecule? A)aseptic acid and oxaloactate B)glutamine and glutamate C)alanine and pyruvate D)All of the answer are correct E)None of the answers is correct

D)all of the answers are correct

If you received a laboratory report showing the prescence of high concentration of phenylalanine and its metabolites in the urine of a patient , what disease would you suspect ?

Disease : Phenylketonuria (PKU) This disease can arise from a defect in the enzyme phenylalanine hydroxylase , which converts phenylalanine to tyrosine or a defect in the production of tetrahydrobiopterin

During starvation more urea production occurs..Explain this observation ?

During starvation , your body will seek out your cellular proteins to be used as fuel. The cellular proteins will be degraded and their carbon skeletons are oxidized for energy . During that first step of amino acid catabolism there is a removal of amino groups , which is excited as urea.

In the digestion of protein that occurs in the small intestine , which enzyme is critical in the activation of zymogens ?

Enteropeptidase

Describe the role of gastrin , pepsinogen , cholecystokinin , and enteropeptidase in protein digestion?

Gastrin = stimulate the parietal cells to release HCl and stimulate chief cells to release pepsinogen Pepsinogen = the low ph from the gastric juice will stimulate the conversion to pepsin , which will begin the protein degradation int he stomach Cholecystokinin = this is a hormone that will stimulate the secretion of the zymogens to enter the small intestines Enteropeptidase = a proteolytic enzyme that activates trypsinogen in the small intestines to be converted to trypsin , whereas trypsin will activate the the remaining zymogens into their active forms .

Degradation of amino acid yields compounds that are common intermediates in the major metabolic pathways. Explain the distinction between glycogenic and ketogenic amino acids in terms of their metabolic fates ?

Glycogenic amino acids are those amino acids that are catoablaized into intermediates that serve for gluconeogenis (alpha-ketoglutartate , succinyl-CoA, fumarate, oxaloacetate , and pyruvate) to produce glucose . Ketogenic amino acids are the ones that are catabolized to yield Acetyl-CoA or acetoacetyl-CoA , which are the precursors for Ketone body formation

Why does a mammal go to all of the trouble of making urea from ammonia rather than simply excreting ammonia as many bacteria do?

In contrast to bacteria, ammonia produced by amino catobolism in mammals cannot be sufficiently diluted int he tissues and the blood to avid accumulating at toxic levels , which can to lead to various issues within our body. Therefore, by generating urea , we create a non-toxic from of ammonia . Bacteria has the ability to dilutes its ammonia to nontoxic levels in surrounding mediums.

Describe the reactions and the role of glucose -alanine cycle .

In this cycle we are ultimately transferring toxic ammonia from the muscle to the liver via alalnine , the non-toxic form . The muscle protein in muscles will breakdown to amino acids and into free ammonia (NH4+), that will be picked up by glutamate. Inside the muscle you will have pyruvate already produced from glycolysis and will eventually convert to alanine through a transmaination . Glutamate will come in and donate its ammonia group to pyruvate to generate alanine with the enzyme alanine aminotransferase. Alanine will now enter the blood and travel to the liver. Once in the liver, alanine will transfer the amino group back to glutamate by the use of alanine aminotransferase in the reverse reaction. Glutamate will then go through its process to release ammonia safely as urea in the urea cycle. Since the alanine gave up its amino group it will convert back into pyruvate. Pyruvate in the liver will be used in gluconeogenesis to produce glucose .The glucose produced in the liver will travel into the blood to the muscle. Glucose will be utilized in glycolysis to produce pyruvate and thus the cycle can begin again .

Describe the reaction in which ammonia is formed from glutamate?

In this reversible process Glutamate will undergo oxidation via (NAD(P)+ to NAD(P)H) this oxidation will leave the amino group free to be acted upon by H20 to generate NH4+ and leave. Since the amino group has left we are left with the group known as alpha ketoglutarate . During this process glutamate dehydrogenase is being used. This can also be called an oxidative deamination process as well. Remember that the use of NAD or NADP is what makes this reaction so unique

Describe the roles of glutamine synthetase and glutaminase in the metabolism of amino groups in mammals ?

In tissues that are metabolized the carbon skeletons of amino acids , the amino groups are transferred by transamination to glutamate , then released as ammonia . Ammonia which is toxic will be combined to glutamate to form glutamine , the reaction is catalyzed by glutamine synthetase and requires ATP . Glutamine is moved from the extra hepatic tissue to the liver and kidneys where the amino group is release from glutamine by glutaminase : the products are glutamate and ammonia . The ammonia delivered in this way to liver is converted to urea , then excreted

The human genetic disease phenylketonuria (PKU) can result from? A)deficiency of protein in the diet B) inability to catabolize ketone bodies C)inability to convert phenylalanine to tyrosine D)inability to synthesizes phenylalanine E)production of enzymes containing no phenylalanine

Inability to convert phenylalanine to tyrosine , due to a defect in the enzyme phenylalanine hydroxylase

What are the chemical intermediates , in the role of pyridoxal phosphate (PLP) in the transamination of an amino acid

Intermediates: 1.Pyridoxal phospahte (internal aldimine ) 2.Schiff Base (external aldimine) 3.Quinonoid Intermediate 4.Rearranged Quinonoid intermediate 5.Pyridoxamine Phosphate and a alpha keto acid Transamination= in this reaction Pyridoxal phosphate ( internal aldimine) combined with an amino acid attaching to its active site will generate a schiff base ( external aldimine ) . The external aldimine will have an abstraction of a hydrogen to generate a quinonoid intermediate . The lone pairs present in the quinoid intermediate will kick off hydrogen and rearrange itself. The newly rearranged quinonoid intermediate will go through hydrolysis to produce an alpha -keto acid and pyridoxamine phosphate , whereas the pyridoxamine phosphate will contain the amino group . This can also be reference as a Ping Pong reaction

Which of these amino acids are both ketogenic and glucogenic ? 1.Isoleucien 2. Vaine 3.Histidine 4.Arginine 5.Tyrosine

Isoleucine and Tyrosine

Which fo the following is not true of the reaction catalyzed by glutamate dehydrogenase ? A) It is similar to transamination in that it involves the coenzyme pyridoxal phosphate (PLP) B)NH4+ is produced C)The enzyme can use either NAD+ or NADP+ as a cofactor D) The enzyme is glutamate-specific , but the reaction is involved in oxidizing other amino acids E) Alpha- ketoglutamate is produced from amino acid

It is similar to transamination intuit it involves the coenzyme pyridoxal phosphate (PLP)

Which statement is False regarding ketogenic and glycogenic amino acids ? A)Glucogenic amino acids cannot be used to make ketone bodies B)Ketogenic amino acids can be used to synthesized fatty acids C)Leucien and Isoleycine are both exclusively ketogenic amino acids D)Both valine and threonine catabolisam produce succinyl-CoA

Leucine and Isoleucine are both exclusively ketogenic amino acids

Which substance is NOT involved in the production of urea from NH4+ via the urea cycle ? A)Aspartate B)ATP C)Carbamoyl phospahte D)Malate E)Ornithine

Malate

Describe the degradative pathway of proline to an intermediate of the wither glycolysis or the citric acid cycle . Show structures of intermediates and indicator where cofactors are involved?

Proline will be oxidized using the enzyme proline oxidase on the carbon furthest from the carboxyl group to generate a schiff base , delta^1- Pyrroline-5-carboxylate. delta^1- Pyrroline-5-carboxylate will be hydrolyzed to Glutamate gamma semialdehyde. Glutamate gamma-semialdehyde will be oxidized on the furthest carbon from the carboxyl group by glutamate semialdehyde dehydrogenase to generate glutamate, in the process NAD(P)+ to NAD(P)H+H. Glutamate will go through a deamination process using glutamate dehydrogenase , to kick off the NH4+ group and have a transfer of elections NAD(P)+ to NAD(P)H+H to alpha-ketoglutarate.

The coenzyme involved in a transaminase reaction is ?

Pyridoxal phosphate (PLP)

The coenzyme required for all transaminations is derived from: A) niacin. B) pyridoxine (vitamin B6). C) riboflavin. D) thiamin. E) vitamin B12.

Pyridoxine (vitamin b6)

The Amino acids serine, alanine, and cysteine can be carbolized to yield? A)fumarate B)Pyruvate C)succinate D)alpah-ketoglutarte E)none of the above

Pyruvate (6 amino acids : serine, glycine , alanine , cysteine, threonine , tryptophan)

Name one amino acid whose oxidation proceeds via the intermediate shown: (a) pyruvate; (b) oxaloacetate; (c) α -ketoglutarate; (d) succinyl-CoA; (e) fumarate.

Pyruvate : serine Oxaloacetate : aspargine alpha ketogluatarate : arginine succinyl-CoA: threonine Fumarate : phenylalanine *This is just one of the amino acids *

Which compound is used in single carbon transfer reactions ?

S-adneosyl methionine , tetrahydrofolate , biotin

Which of theses is not a protease that acts in the small intestines ? A)Chymotrypsin B)Elastase C)Enteropeptidase D) Secretin E) Trypsin

Secretin

In the treatment too diabetes, insulin is given intravenously (under the skin). Why can't this hormone , a small protein , be taken orally?

Since insulin is a protein it be destroyed /broken down by the low pH of the gastric juice and various proteases that act in the small intestines for degradation. Secondly , if insulin escaped the degradation process in the intestines , it would not enter the bloodstream from the intestines , because the intestinal Lumen transports free amino acids , not intact proteins

There are bacteria for which alanine can serve as the chief energy source , they oxidize the carbon skeletons of their amino cid , thereby generating ATP Describe the first step in alanine degradation and show any cofactors?

The first sep in alanine degradation is the removal of a amino group by transamination reaction. The cofactor PLP (pyridoxal phosphate ) will help as alpha-ketoglutarte accepts the amino group of alanine using the enzyme alanine aminotransferase to be generate glutamate and pyruvate.

Which of the following statements is false in reference to the mammalian synthesis of urea? a)Krebs cycle was a major contributor to the elucidation of the pathway involved B) The Amino acid arginine is the immediate precursor to urea C)The carbon atom of urea is derived form mitochondria H20 D) The precursor to one of the nitrogens of urea is aspartate E) The process of urea production is an energy yielding series of reactions

The process of urea production is NOT an energy yielding series of reactions

What are the reactants and products in the transamination reaction in which glutamate and pyruvate are the starting materials . What cofactor is required for this reaction?

The reactants : glutamate and pyruvate The products : alpha-ketoglutarate and alanine Cofactor : PLP (pyridoxal phosphate )

Which statement is TRUE regarding glutamine synthetase?

This enzyme is classified asa a ligase , and an intermediate in the reaction catalyzed

In amino acid catabolism, the first reaction for many amino acids is a(n): A) decarboxylation requiring thiamine pyrophosphate (TPP). B) hydroxylation requiring NADPH and O2. C) oxidative deamination requiring NAD+. D) reduction requiring pyridoxal phosphate (PLP). E) transamination requiring pyridoxal phosphate (PLP).

Transamination requiring pyridoxal phosphate

Which compound is a zymogen that can be converted to an endopeptidase that hydrolyzes peptide bonds adjacent to LYS and ARG residues ?

Trypsinogen

Which of the following is a ZYMOGEN that can be converted to a endopeptidase that hydrolyzes peptide bind adjacent to Lys and Arg residues ? A) Chymotrypinsogen B)Pepsin C)pepsinogen D)Trypsin E) Trypsinogen

Trypsinogen

If a person's urine contains unusually high concentration of urea , which one of the following diets has he or she probably been eating recently ? A)High carbohydrates, very low proteins B)Very high carbohydrates, no protein , no fat C)Very very high fat, high carbs, no proteins D)Very high fat , very low proteins E)Very low carbohydrates, very high proteins

Very low carbohydrates , very high proteins

Amino acid catabolism invlvioes the breakdown of 20 amino acids all of which contain nitrogen but have different carbon skeletons . What overall strategy is used to deal with this problem?

When amino acids enter the liver their nitrogen groups are removed in a transamination reaction to glutamate. This will convert the amino acid to an alpha keto acid that is now used as an intermediate or is used to create an intermediate

Describe the fundamental nutrition problem faced by individuals with genetic defects in enzymes involved in urea formation and what are the approaches to treatment of these diseases.

When there is genetic defect in the enzymes for urea formation you will most likely form toxic blood levels of ammonia from the breakdown of ingested proteins that are not be properly excreted out the body. Therefore , you will need to limit your intake of amino acids . However, you cannot completely stop your ingestion of amino acids , because some amino acid are essential to human biological pathways. Thus , you must ingest the the adequate amounts that are necessary. medical personnel will usually administer benzoate and phenylbutyrate. They do this because they most likely direct high levels of free ammonia not being processed through the urea cycle and excreted out the body and therefore its a rise in toxic ammonia in the body and we are not at a homeostasis However by administering benzoate the enzyme glycine will be taken up to produce hippurate to be excreted safely out the body. This will end up glycine to be regenerated since it was used up in this reaction to take up ammonia in a glycine synthase reaction . By administering phenylbutyrate we will end up taking up glutamine to generate phenylacetylglutamine and phenylacetylglutamine is able to exit the body through the urine in a non-toxic form. BY taking up the glutamine , we are helping the body to upregulate the enzyme , glutamine synthetase . Glutamine synthetase reaction will then help in to take up ammonia groups and exit the body through urea in a non-toxic fashion.

Catabolism fo which substance can exert the citric acid cycle as succinyl-CoA ? A)threonine B)odd- numbered fatty acids C)methionine D)all of the answers are correct E)none of the answers is correct

all of the answers are correct

What enzymes classes are responsible for introverting glutamate and alpha-ketoglutartate ?? A)hydrolyses B)transferases C)ligases D)All of the answers are correct E)none of the answers is correct

all of the answers are correct

A possible product of isoleucine catabolism is ? A)acetyl-CoA B)succinyl-CoA C)conversion to alpha keto isoleucine D)all the answers are correct E)none of the answers is correct

all the answer are correct

Conversion of serine two glycine requires which cofactor ? A)tetrahydrofolate B)pyridoxal 5'phospahte C)NADH D)All of the answers are correct E)none of the answers is correct ?

all the answers are correct

Which product is created during the conversion of threonine not glycine during amino acid catabolism ? A)acetyl-CoA B)water C)NADH D)both acetyl-CoA and NADH E)both water and NADH

both acetyl -CoA and NADH

Which amino acid can be considered to be both glycogenic and ketogenic ? A)threonine B)aspartate C)leucine D)isoleucine E)tithe threonine and isoleucine

both threonine and isoleucine

In the urea cycle, ornithine transcarbamoylase catalyzes: A) cleavage of urea to ammonia. B) formation of citrulline from ornithine and another reactant. C) formation of ornithine from citrulline and another reactant. D) formation of urea from arginine. E) transamination of arginine.

formation of citrulline from orninithine and another reactant

Which hormone is triggered by the entry of protein into the stomach ?

gastrin

The conversion of glutamate to an alpha -ketoacid and NH4+ is catalyzed by what enzyme ?

glutamate dehydrogenase

Which amino acid can be directly converted into a citric acid cycle intermediate by transamination? A)glutamic acid B)serine C)threonine D)tyrosine E)proline

glutamic acid

Which reaction involving an amino acid CANNOT be stalked via a PLP dependent mechanism ? a)hydrolysis B)decarboxylatin C)racemization D)transmaination E)treansimination

hydrolysis

The conversion glutamate to an alpha-to acid and NH4+ : A)does not require any cofactors B)is a reductive deamination C)is accompanied by ATP hydrolysis catalyzed by the same enzyme D)is catalyzed by glutamate dehydrogenase E)requires ATP

is catalyzed by glutamate dehydrogenase

Urea synthesis in mammals takes place primarily in tissues of the: A) brain. B) kidney. C) liver. D) skeletal muscle. E) small intestine.

liver

Which compound is NOT and intermediate is the conversion of alanine's carbon skeleton into that of aspartate ? A)acetyl-CoA B)pyruvate C)lactate D)oxalocaetate E)neither acetyl-CoA nor lactate

neither acetyl-CoA not lactate

If C-labeled glutamate is introduced into liver cells , what compounds in the urea cycle will be rapidly labeled with the carbon ? A)ornithine B)aspartate C)arginine D)urea E) none of the answers is correct

none of the answers are correct

Which statement is FALSE regarding pyridoxal phosphate ? A)the prosthetic group is critical in aminotransferases reactions B) This cofactor can form covalent bonds to lysine residues enzyme C)This cofactor can form covalent bonds to some intermediates D) This cofactor carries both positive and negative formal charges E) non e of the statements is false

none of the statements is false

If N-labeled glutamate is introduced into liver cells , what compounds in the urea cycle will NOT be rapidly labeled with the nitrogen ? A)ornithine B)aspartate C)arginine D)urea E)both ornithine and aspartate

ornithine

Glutamate is metabolically converted to alpha-ketoglutarate and NH4+ by a process known as what ?

oxidative deamination

In Human genetic disease maple syrup urine disease , the metabolic defect involves what to stop occurring ?

oxidative decarboxylation

Under which circumstances are amino acids NOT metabolized via oxidative degradation ? A)starvation B)plants growing in nutrient -rich soils C)normal protein turnover D)a diet rich proteins E)uncontrolled diabetes

plants growing in nutrient rich soils

Transamination from alanine to alpha -ketoglutamate requiresWhat coenzyme ?

pyridoxal phosphate (PLP)

Serine or cysteine may enter the citric acid cycle as acetyl-CoA after conversion to what ?

pyruvate

Which reaction associated with the urea cycle occurs int he cytosol ? A)the synthesis of carbamoyl phosphate B) the synthesis of citrulline C)the synthesis of arginosuccinate D)the synthesis of both carbamoyl phosphate and citrulline E)the synthesis of both citrulline and arginaosuccinate

the synthesis of arginosuccinate

Pyridoxal phosphate is a cofactor in what class of reactions ? A)acetylation B)desulfurization C)methylation D)reducation E)transamination

transamination

Serotonin is produced from the metabolism of which amino acid? A)valine B)serine C)cysteine D)tyrosine E)tryptophan

tryptophan

Conversion of ornithine to citrulline is asap in the synthesis of what excretion product?

urea