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?

Aspartate Signup and view all the answers

Which substance is a product of the oxidative deamination process?

α-Ketoglutarate Signup and view all the answers

Which molecule activates glutamate dehydrogenase?

ADP Signup and view all the answers

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

Arginine Signup and view all the answers

In which organs does the oxidative deamination primarily occur?

Liver and kidneys Signup and view all the answers

What role does α-ketoglutarate play in metabolism?

It is an intermediate of the TCA cycle. Signup and view all the answers

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

Phosphoenolpyruvate Signup and view all the answers

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

Transamination Signup and view all the answers

What is the role of tyrosine in relation to phenylalanine?

Synthesis by one-step hydroxylation Signup and view all the answers

Which amino acid is categorized under the Essential Amino Acids?

Isoleucine Signup and view all the answers

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

To kill some bacteria Signup and view all the answers

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

Pepsinogen Signup and view all the answers

What initiates the activation of pancreatic zymogens?

Release of cholecystokinin and secretin Signup and view all the answers

What is the role of aminopeptidase in protein digestion?

To cleave N-terminal residues from oligopeptides Signup and view all the answers

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

Removal of the α-amino group Signup and view all the answers

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

Amino acids from dietary protein. Signup and view all the answers

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

It can be excreted or incorporated into other compounds Signup and view all the answers

Which step is NOT part of the urea cycle process?

Energy production from amino acids Signup and view all the answers

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

Amino acids cannot be synthesized in the body. Signup and view all the answers

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

They have different specificity for amino acid R-groups Signup and view all the answers

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

Liver Signup and view all the answers

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

Deamination Signup and view all the answers

How does the amino acid pool get depleted?

Through synthesis of body proteins. Signup and view all the answers

Which statement about the absorption of dietary proteins is true?

Proteins must be hydrolyzed into di- and tripeptides before absorption. Signup and view all the answers

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

They are rapidly degraded. Signup and view all the answers

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

Activating pepsinogen to pepsin. Signup and view all the answers

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

To transfer α-amino groups to α-ketoglutarate Signup and view all the answers

Which enzyme is primarily responsible for facilitating transamination reactions?

Aminotransferase Signup and view all the answers

Which coenzyme is required by all aminotransferases during transamination?

Pyridoxal phosphate (PLP) Signup and view all the answers

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

Ammonia Signup and view all the answers

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

Oxaloacetate Signup and view all the answers

Which statement about transamination is true?

It is reversible. Signup and view all the answers

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

Alanine aminotransferase (ALT) Signup and view all the answers

What effect does transamination have on the amino acids involved?

It reallocates amino groups without net deamination. Signup and view all the answers

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

To catalyze the formation of carbamoyl phosphate from NH3 and HCO3- Signup and view all the answers

Which enzyme is responsible for the cleavage of argininosuccinate?

Argininosuccinase Signup and view all the answers

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

It activates CPS I allosterically Signup and view all the answers

Which amino acids are classified as glucogenic?

Those converted to glucose precursors such as pyruvate Signup and view all the answers

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

Acetyl-CoA and Acetoacetate Signup and view all the answers

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

Ornithine Signup and view all the answers

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

Increased glutamate concentration leads to increased N-acetylglutamate synthesis Signup and view all the answers

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

They must be obtained from dietary sources. Signup and view all the answers

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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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!