Biochemistry Amino Acid Metabolism Quiz
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Questions and Answers

What is released during oxidative deamination by glutamate dehydrogenase?

  • Carbon dioxide
  • Glutamate
  • Free ammonia (correct)
  • α-Ketoglutarate

Which coenzymes can glutamate dehydrogenase utilize?

  • CoA and FADH2
  • NAD+ and FAD
  • NADH and NADPH
  • NAD+ and NADP+ (correct)

Which molecule acts as an allosteric inhibitor of glutamate dehydrogenase?

  • ADP
  • ATP
  • GTP (correct)
  • NADH

What is one nitrogen source for the formation of urea in the urea cycle?

<p>Aspartate (D)</p> Signup and view all the answers

Which substance is a product of the oxidative deamination process?

<p>α-Ketoglutarate (D)</p> Signup and view all the answers

Which molecule activates glutamate dehydrogenase?

<p>ADP (A)</p> Signup and view all the answers

Which of the following amino acids is only essential in children and not in adults?

<p>Arginine (B)</p> Signup and view all the answers

In which organs does the oxidative deamination primarily occur?

<p>Liver and kidneys (B)</p> Signup and view all the answers

What role does α-ketoglutarate play in metabolism?

<p>It is an intermediate of the TCA cycle. (B)</p> Signup and view all the answers

Which metabolic intermediate is NOT involved in the synthesis of nonessential amino acids?

<p>Phosphoenolpyruvate (C)</p> Signup and view all the answers

What process is primarily responsible for the conversion of 3-phosphoglycerate to serine?

<p>Transamination (B)</p> Signup and view all the answers

What is the role of tyrosine in relation to phenylalanine?

<p>Synthesis by one-step hydroxylation (C)</p> Signup and view all the answers

Which amino acid is categorized under the Essential Amino Acids?

<p>Isoleucine (A)</p> Signup and view all the answers

What is one of the primary functions of hydrochloric acid in the stomach?

<p>To kill some bacteria (C)</p> Signup and view all the answers

Which enzyme is secreted by the chief cells of the stomach as an inactive zymogen?

<p>Pepsinogen (C)</p> Signup and view all the answers

What initiates the activation of pancreatic zymogens?

<p>Release of cholecystokinin and secretin (D)</p> Signup and view all the answers

What is the role of aminopeptidase in protein digestion?

<p>To cleave N-terminal residues from oligopeptides (D)</p> Signup and view all the answers

What is the first step in the catabolism of amino acids?

<p>Removal of the α-amino group (B)</p> Signup and view all the answers

Which of the following correctly describes the sources of the amino acid pool?

<p>Amino acids from dietary protein. (A), Amino acids provided by the degradation of body proteins. (B)</p> Signup and view all the answers

What occurs to the nitrogen after being removed from amino acids?

<p>It can be excreted or incorporated into other compounds (B)</p> Signup and view all the answers

Which step is NOT part of the urea cycle process?

<p>Energy production from amino acids (D)</p> Signup and view all the answers

What is the primary reason amino acids must be obtained from the diet?

<p>Amino acids cannot be synthesized in the body. (A)</p> Signup and view all the answers

Which of the following best describes the role of proteases in protein digestion?

<p>They have different specificity for amino acid R-groups (D)</p> Signup and view all the answers

Which organ does NOT produce proteolytic enzymes necessary for protein digestion?

<p>Liver (C)</p> Signup and view all the answers

Which process converts amino acids' amino-nitrogen into urea for excretion?

<p>Deamination (A)</p> Signup and view all the answers

How does the amino acid pool get depleted?

<p>Through synthesis of body proteins. (C)</p> Signup and view all the answers

Which statement about the absorption of dietary proteins is true?

<p>Proteins must be hydrolyzed into di- and tripeptides before absorption. (D)</p> Signup and view all the answers

What happens to excess amino acids beyond the biosynthetic needs of a cell?

<p>They are rapidly degraded. (A)</p> Signup and view all the answers

Which of the following is a function of gastric juice in protein metabolism?

<p>Activating pepsinogen to pepsin. (D)</p> Signup and view all the answers

What is the primary role of transamination in amino acid catabolism?

<p>To transfer α-amino groups to α-ketoglutarate (A)</p> Signup and view all the answers

Which enzyme is primarily responsible for facilitating transamination reactions?

<p>Aminotransferase (C)</p> Signup and view all the answers

Which coenzyme is required by all aminotransferases during transamination?

<p>Pyridoxal phosphate (PLP) (D)</p> Signup and view all the answers

What is the primary end product of oxidative deamination of glutamate?

<p>Ammonia (D)</p> Signup and view all the answers

During transamination to form aspartate, which substance does glutamate donate its amino group to?

<p>Oxaloacetate (D)</p> Signup and view all the answers

Which statement about transamination is true?

<p>It is reversible. (C)</p> Signup and view all the answers

Which of the following is an example of an aminotransferase enzyme?

<p>Alanine aminotransferase (ALT) (A)</p> Signup and view all the answers

What effect does transamination have on the amino acids involved?

<p>It reallocates amino groups without net deamination. (C)</p> Signup and view all the answers

What is the function of carbamoyl phosphate synthetase (CPS) in the urea cycle?

<p>To catalyze the formation of carbamoyl phosphate from NH3 and HCO3- (A)</p> Signup and view all the answers

Which enzyme is responsible for the cleavage of argininosuccinate?

<p>Argininosuccinase (C)</p> Signup and view all the answers

What role does N-acetylglutamate play in the urea cycle?

<p>It activates CPS I allosterically (B)</p> Signup and view all the answers

Which amino acids are classified as glucogenic?

<p>Those converted to glucose precursors such as pyruvate (A)</p> Signup and view all the answers

Which metabolic intermediates are associated with the degradation of ketogenic amino acids?

<p>Acetyl-CoA and Acetoacetate (C)</p> Signup and view all the answers

What is the end product of arginase activity in the urea cycle?

<p>Ornithine (C)</p> Signup and view all the answers

How does the concentration of glutamate affect the synthesis of N-acetylglutamate?

<p>Increased glutamate concentration leads to increased N-acetylglutamate synthesis (C)</p> Signup and view all the answers

Which of the following statements about essential amino acids is correct?

<p>They must be obtained from dietary sources. (A)</p> Signup and view all the answers

Flashcards

Amino Acid Pool

The body's total amount of free amino acids that are available for use in protein building, energy production, or other metabolic processes.

Protein Turnover

The continuous breakdown and synthesis of proteins in the body.

Protein Digestion

The process of breaking down proteins into amino acids. Occurs primarily in the stomach and small intestine.

Proteolytic Enzymes

Enzymes that break down proteins. They are produced in the stomach, pancreas, and small intestine.

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Deamination

The process of removing the amino group (NH2) from an amino acid. This is the first step in amino acid catabolism.

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Transamination

The transfer of an amino group from one molecule to another. It's a crucial step in the synthesis of non-essential amino acids and the production of energy from amino acids.

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Urea

A nitrogenous waste product produced in the liver and excreted by the kidneys.

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Carbon Skeleton Conversion

The process of converting the carbon skeleton of an amino acid into glucose, glycogen, fatty acids, or ketone bodies. This allows the body to use the energy contained in amino acids.

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What is Transamination?

The funnelling of amino groups to glutamate. It's the first step in amino acid catabolism, where an α-amino group is transferred to α-ketoglutarate.

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What are Aminotransferases?

An enzyme that facilitates the transfer of α-amino groups in transamination reactions.

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What is Alanine Aminotransferase (ALT)?

An aminotransferase that plays a role in breaking down amino acids, turning alanine into pyruvate and α-ketoglutarate into glutamate. It's critical for providing energy from amino acids.

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What is Aspartate Aminotransferase (AST)?

An aminotransferase that transfers amino groups from glutamate to oxaloacetate, producing aspartate. This is essential for converting nitrogen from amino acids into urea.

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What is Pyridoxal Phosphate (PLP)?

A derivative of vitamin B6 that serves as a coenzyme for aminotransferases. It plays a crucial role in the transfer of amino groups.

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What is Oxidative Deamination?

A process that removes the amino group (NH2) from glutamate, producing ammonia and α-ketoglutarate. It's crucial for releasing nitrogen from amino acids and generating energy.

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What is Urea?

A nitrogenous waste product produced in the liver as a result of amino acid catabolism. It's excreted from the body by the kidneys.

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How are Transamination and Oxidative Deamination connected?

Transamination redistributes amino groups, but it doesn't get rid of them. The nitrogen from amino groups is released through Oxidative Deamination, producing ammonia as a byproduct.

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What is the role of hydrochloric acid in protein digestion?

Hydrochloric acid (HCl) is a powerful acid found in the stomach. It helps break down food by killing some bacteria and denaturing proteins. Denaturation makes proteins easier to digest by enzymes.

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What is pepsin?

Pepsin is a type of enzyme that breaks down proteins within the stomach. It works best in acidic environments.

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What is the role of pancreatic proteases in protein digestion?

Pancreatic proteases are enzymes released by the pancreas that further break down protein fragments into smaller peptides and amino acids in the small intestine.

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What does aminopeptidase do for protein digestion?

Aminopeptidase is an enzyme found on the surface of the small intestine that breaks off amino acids from the N-terminus (end) of peptides, further reducing them to individual amino acids.

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Why is removing the amino group important for amino acid metabolism?

Removing the amino group from an amino acid is the first step in breaking down amino acids for energy or converting them into other compounds.

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What is the urea cycle?

The urea cycle is a metabolic pathway in the liver that converts ammonia (NH3) into urea, the main form of nitrogenous waste excreted in urine.

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What are essential amino acids?

These are amino acids that our body can't synthesize and must be obtained from the diet. Examples include phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, histidine, leucine, and lysine.

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What are non-essential amino acids?

These amino acids are produced by our body from common metabolites. They don't need to be consumed directly through the diet. Examples include alanine, asparagine, glycine, serine, and tyrosine.

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What is Deamination?

This process involves removing the amino group (NH2) from an amino acid, producing ammonia (NH3) as a byproduct.

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How is amino-nitrogen transformed for excretion?

This is the primary method of removing nitrogen from the body in the form of urea. Urea is synthesized in the liver and excreted through the kidneys.

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Oxidative Deamination of Glutamate

The process of removing the amino group from glutamate, releasing free ammonia and generating α-ketoglutarate, a key intermediate in the TCA cycle.

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Glutamate Dehydrogenase

An enzyme that catalyzes the oxidative deamination of glutamate, using either NAD+ or NADP+ as a coenzyme.

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Oxidative Deamination

The main source of ammonia in the body, produced by the breakdown of amino acids.

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α-Ketoglutarate

An intermediate in the TCA cycle, produced by oxidative deamination of glutamate.

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Amino Acid Catabolism

The process of breaking down amino acids to generate energy or convert them into other molecules.

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Transport of Ammonia

The primary means of safely transporting excess ammonia from tissues to the liver.

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Urea Cycle

The series of reactions that convert ammonia into urea, removing excess nitrogen from the body.

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What is the rate-limiting enzyme in the urea cycle?

Carbamoyl phosphate synthetase I (CPS I) is the rate-limiting enzyme in the urea cycle. It catalyzes the condensation of ammonia (NH3), carbon dioxide (CO2), and ATP to form carbamoyl phosphate.

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What does ornithine transcarbamoylase do?

Ornithine transcarbamoylase is an enzyme that catalyzes the transfer of a carbamoyl group from carbamoyl phosphate to ornithine, producing citrulline.

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What is the role of argininosuccinate synthetase?

Argininosuccinate synthetase is an enzyme that adds the second nitrogen atom to the urea molecule by combining citrulline with aspartate to form argininosuccinate.

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What is the final step in the urea cycle?

Arginase is an enzyme that cleaves arginine into ornithine and urea, releasing urea as a waste product.

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What is the role of N-acetylglutamate in the urea cycle?

N-acetylglutamate acts as an allosteric activator of CPS I, increasing the activity of the enzyme and promoting urea synthesis.

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What are glucogenic amino acids?

Glucogenic amino acids are broken down into intermediates that can be used to synthesize glucose.

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What are ketogenic amino acids?

Ketogenic amino acids are broken down into intermediates that can be used to produce ketone bodies, which can be used as fuel for energy.

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Study Notes

Nitrogen Metabolism Learning Objectives

  • Amino acids pool and protein turnover in nitrogen metabolism are described.
  • Protein digestion and absorption in the body are explained.
  • The overall catabolism of amino acids, including transamination and deamination, is outlined.
  • The transformation of amino-nitrogen to urea for excretion is explained.
  • The conversion of carbon skeletons from proteins to glucose or ketone bodies is illustrated.
  • The synthesis of nonessential amino acids is described.
  • Amino acids are not stored in the body.
  • Amino acids are obtained from diet, synthesized de novo, or from protein degradation.
  • Excess amino acids are rapidly degraded.
  • Amino acid catabolism is part of nitrogen-containing molecule metabolism.
  • Nitrogen enters the body through food and leaves as urea, ammonia, and other products.
  • Body proteins' role in transformations involves the amino acid pool and protein turnover.
  • The amino acid pool comes from body protein degradation, dietary protein, and nonessential amino acid synthesis.
  • The amino acid pool is depleted through protein synthesis, usage as precursors, or conversion to other molecules.
  • Dietary protein intake can vary significantly, with 100g/day being a typical amount.
  • Body protein turnover is about 400g/day.

Digestion of Dietary Proteins

  • Proteins are too large for direct absorption.
  • Proteins are hydrolyzed into di- and tripeptides and individual amino acids for absorption.
  • Proteolytic enzymes from the stomach, pancreas, and small intestine degrade proteins.

Digestion of Proteins by Gastric Secretion

  • Stomach produces gastric juice containing hydrochloric acid and pepsinogen (proenzyme).
  • Hydrochloric acid kills bacteria and denatures proteins, making them susceptible to protease hydrolysis.
  • Pepsinogen is activated to pepsin by HCl or autocatalysis.
  • Pepsin cleaves dietary proteins into peptides and some amino acids.

Digestion of Proteins by Pancreatic Enzymes

  • Pancreatic proteases further break down polypeptides from the stomach into oligopeptides and amino acids.
  • Pancreatic proteases have different specificities for amino acid R-groups.
  • Pancreatic zymogens are synthesized and secreted as inactive forms and are activated and released by cholecystokinin and secretin.

Digestion of Oligopeptides in the Small Intestine

  • The luminal surface of the small intestine contains aminopeptidases (exopeptidases).
  • Aminopeptidases repeatedly cleave N-terminal residues from oligopeptides to form smaller peptides and free amino acids.

Overview of Amino Acid Catabolism

  • Amino acids are metabolized to produce energy, used in gluconeogenesis, or incorporated into other compounds.
  • Amino acids are converted to one of seven metabolic intermediates (pyruvate, a-ketoglutarate, succinyl CoA, fumarate, oxaloacetate, acetyl CoA, and acetoacetate.).

Breakdown of Amino Acids

  • Amino acids are degraded to compounds metabolized into CO2 and H2O or used in gluconeogenesis.
  • Amino acids can be either glucogenic or ketogenic.
  • Glucogenic amino acids are converted to glucose precursors.
  • Ketogenic amino acids are converted to acetyl CoA or acetoacetate, which can form fatty acids or ketone bodies.

Amino Acid Biosynthesis

  • Essential amino acids cannot be synthesized in sufficient quantities and must be obtained from the diet.
  • Nonessential amino acids can be synthesized by the body from common metabolites.
  • Tyrosine is synthesized from phenylalanine.

Nitrogen Removal

  • Removing the amino group is essential for producing energy from amino acids.
  • The nitrogen can be incorporated into other compounds or excreted.
  • The carbon skeleton remains metabolized.

Transamination

  • Transamination, the first step in amino acid catabolism, involves the transfer of an amino group from an amino acid to a-ketoglutarate, forming glutamate and a keto acid.
  • The enzyme aminotransferase catalyzes transamination reactions.

Oxidative Deamination

  • Glutamate can be oxidatively deaminated to release ammonia (NH3) by glutamate dehydrogenase.
  • This occurs primarily in liver and kidney.
  • Glutamate dehydrogenase can use either NAD+ or NADP+ as a coenzyme.
  • a-Ketoglutarate is an intermediate of the TCA cycle and is regenerated.

Urea Cycle

  • The urea cycle is responsible for removing excess nitrogen from the body through nitrogen excretion.
  • The urea cycle transforms amino-nitrogen into urea for excretion.
  • The urea molecule's nitrogen comes from free ammonia and aspartate.
  • The carbon and oxygen of urea are derived from CO2.
  • Urea is produced in the liver and transported to kidneys for excretion.

Urea Cycle Reactions

  • Formation of carbamoyl phosphate
  • Formation of citrulline
  • Synthesis of argininosuccinate
  • Cleavage of argininosuccinate
  • Cleavage of arginine to ornithine and urea

Urea Cycle Regulation

  • The urea cycle is regulated by substrate availability.
  • CPS I is allosterically activated by N-acetylglutamate.
  • N-acetylglutamate is synthesized from glutamate and acetyl CoA.

Transport of Ammonia

  • Ammonia is transported from tissues to the liver to participate in urea cycle. This most commonly involves interconversion with glutamate to glutamine.

Essential Amino Acids

  • A list of essential amino acids and their corresponding three-letter abbreviations.

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Nitrogen Metabolism PDF

Description

Test your knowledge on amino acid metabolism, including oxidative deamination and the urea cycle. This quiz covers key enzymes, coenzymes, and essential versus nonessential amino acids. Challenge yourself and see how well you understand these critical biochemical processes!

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