Biochemistry Chapter: Amino Acid Metabolism

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Questions and Answers

What is released as a free ammonia during oxidative deamination by glutamate dehydrogenase?

Glutamate

Ammonium ion (correct)

Oxaloacetate

Iminoglutarate

Which coenzymes can glutamate dehydrogenase utilize?

NADH only

FADH2

NAD+ or NADP+ (correct)

Only NAD+

What condition activates glutamate dehydrogenase?

High levels of Citrulline

High levels of ADP (correct)

High levels of NADH

High levels of GTP

What intermediate is formed during the oxidative deamination of glutamate?

α-Ketoglutarate Signup and view all the answers

Which of the following inhibits glutamate dehydrogenase?

GTP Signup and view all the answers

What role does α-ketoglutarate play in the TCA cycle?

It acts as an intermediate. Signup and view all the answers

Which amino acid is considered essential only in children?

Arginine Signup and view all the answers

How is urea produced in the urea cycle?

From free ammonia and aspartate Signup and view all the answers

Which metabolite signaling the need to generate energy activates glutamate dehydrogenase?

ADP Signup and view all the answers

What is the primary method by which nonessential amino acids are synthesized?

Transamination of α-keto acids Signup and view all the answers

Which of the following is NOT a common metabolic intermediate for the synthesis of nonessential amino acids?

Sucrose Signup and view all the answers

Which reaction is responsible for the conversion of 3-phosphoglycerate to serine?

Transamination Signup and view all the answers

What is the role of tyrosine in amino acid metabolism?

Hydroxylation of phenylalanine Signup and view all the answers

What is the first step in the urea cycle?

Formation of carbamoyl phosphate Signup and view all the answers

Which enzyme is responsible for converting argininosuccinate into arginine?

Argininosuccinase Signup and view all the answers

What effect does an increase in glutamate concentration have on CPS I activity?

Increases CPS I activity Signup and view all the answers

Which of the following amino acids are classified as glucogenic?

Alanine Signup and view all the answers

What triggers the synthesis of N-acetylglutamate?

Increase in glutamate concentration Signup and view all the answers

Which of the following intermediates can be derived from amino acid degradation?

Acetyl-CoA Signup and view all the answers

Which amino acid pathway leads to the formation of ketone bodies?

Ketogenic pathway Signup and view all the answers

What type of amino acids cannot be synthesized by the body and must be obtained from diet?

Essential amino acids 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

What primarily happens to amino acids that are in excess of the biosynthetic needs of the cell?

They are rapidly degraded. Signup and view all the answers

How is pepsinogen activated to pepsin?

By hydrochloric acid or autocatalytically by pepsin Signup and view all the answers

Which of the following correctly describes a source of the amino acid pool?

Amino acids synthesized de novo. Signup and view all the answers

Which of the following best describes the action of pancreatic proteases?

They cleave large polypeptides into oligopeptides and amino acids Signup and view all the answers

What is the primary way nitrogen leaves the body after amino acid metabolism?

As urea. Signup and view all the answers

What triggers the release of pancreatic zymogens for protein digestion?

Cholecystokinin and secretin Signup and view all the answers

What role do proteolytic enzymes play in protein metabolism?

They hydrolyze proteins for absorption. Signup and view all the answers

What role does aminopeptidase play in the digestion of proteins?

It cleaves N-terminal residues from oligopeptides Signup and view all the answers

Which of the following is not a route by which the amino acid pool is depleted?

Loss of waste products. Signup and view all the answers

What is the initial step in the nitrogen removal process from amino acids?

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

In which part of the digestive system are proteolytic enzymes NOT produced?

Large intestine. Signup and view all the answers

What happens to nitrogen after it is removed from amino acids?

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

Which process is responsible for the conversion of amino-nitrogen into urea for excretion?

Deamination. Signup and view all the answers

Which compound is produced as a result of the urea cycle?

Urea Signup and view all the answers

What happens to the carbon skeleton after the deamination of an amino acid?

It can be transformed into glucose or ketone bodies. Signup and view all the answers

What is the primary function of aminotransferases in amino acid catabolism?

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

What coenzyme is essential for all aminotransferases?

Pyridoxal-5'-phosphate (PLP) Signup and view all the answers

Which product is formed during the first transamination reaction?

An α-keto acid Signup and view all the answers

What role does glutamate play in the synthesis of aspartate?

It donates its amino group to oxaloacetate. Signup and view all the answers

What is the end product of glutamate oxidative deamination?

Ammonia Signup and view all the answers

What is true about the process of transamination?

It involves the transfer of an α-amino group. Signup and view all the answers

Which specific aminotransferase primarily functions in the direction of glutamate synthesis?

Alanine aminotransferase (ALT) Signup and view all the answers

What happens during the second transamination reaction involving glutamate?

It produces aspartate and regenerates α-ketoglutarate. Signup and view all the answers

Study Notes

Nitrogen Metabolism Learning Objectives

Amino acid pools and protein turnover in nitrogen metabolism are described.
Protein digestion and absorption processes in the body are detailed.
The overall catabolism of amino acids (transamination and deamination) is outlined.
The transformation of amino-nitrogen into urea for excretion is explained.
The conversion of protein carbon skeletons into glucose or ketone bodies is illustrated.
The synthesis of nonessential amino acids is detailed.
Amino acids are not stored by the body.
Amino acids are obtained through the diet, synthesized de novo, or produced from protein degradation.
Excess amino acids are rapidly degraded.
Amino acid catabolism ispart of the larger process of metabolizing nitrogen-containing molecules
Nitrogen enters the body through food.
Nitrogen leaves the body as urea, ammonia, and other products derived from amino acid metabolism.
Body proteins in these transformations involve two important concepts: the amino acid pool and protein turnover.
The amino acid pool is supplied by three sources: amino acids from body protein degradation, dietary protein, and synthesis of nonessential amino acids.
The amino acid pool is depleted through three routes: synthesis of body protein, precursors of essential nitrogen-containing molecules, and conversion of amino acids to glucose, glycogen, fatty acids, ketone bodies, or CO2 + H2O.
Dietary protein intake can vary, with a typical daily intake of 100g being common in the US.
Proteins are generally too large to be absorbed by the intestine.
Newborns can absorb maternal antibodies in breast milk.
Proteins are hydrolysed to di- and tripeptides and individual amino acids to be absorbed.
Proteolytic enzymes for protein degradation are produced by the stomach, pancreas, and small intestine.
Gastric juices, containing hydrochloric acid and pepsinogen (a proenzyme), are involved in protein digestion in the stomach.
Hydrochloric acid kills bacteria and denatures proteins, making them susceptible to protease hydrolysis.
Pepsin, an acid-stable endopeptidase, is formed from pepsinogen, either by HCl or autocatalysis.
Pepsin cleaves dietary proteins into peptides and free amino acids.
Pancreatic proteases cleave large polypeptides into oligopeptides and amino acids.
Pancreatic proteases have specificities for amino acid R-groups adjacent to the peptide bond.
Pancreatic proenzymes need to be activated by cholecystokinin and secretin.
The small intestine contains aminopeptidases, exopeptidases that cleave N-terminal residues from oligopeptides to yield smaller peptides and free amino acids.
The process of nitrogen removal from amino acids is essential for producing energy, it is an obligatory step in the catabolism of all amino acids.
The nitrogen that is removed can be incorporated into other compounds or excreted.
The carbon skeletons are then metabolized.
Transamination is the first step in amino acid catabolism.
Transamination involves the transfer of an α-amino group from an amino acid to a-ketoglutarate, forming an α-keto acid and glutamate.
Aminotransferases are the enzymes that catalyze transamination reactions.
Transamination does not result in any net deamination.
Glutamate is oxidatively deaminated by glutamate dehydrogenase, releasing ammonia.
Ammonia is a source of nitrogen in urea synthesis.
A-Ketoglutarate is regenerated in the process.
Oxidative deamination results in the release of the amino group as free ammonia (NH3).
Oxidative deamination occurs primarily in the liver and kidney.
Glutamate is unique as the only amino acid that undergoes rapid oxidative deamination.
Glutamate dehydrogenase can use either NAD+ or NADPH as a coenzyme.
a-Ketoglutarate is an intermediate of the TCA cycle.
Activation of glutamate dehydrogenase stimulates flux through the TCA cycle, increasing ATP production.
Glutamate dehydrogenase is allosterically inhibited by GTP and NADH.
Glutamate dehydrogenase is activated by ADP and NAD+.
The direction of these reactions depends on the relative concentrations of glutamate, a-ketoglutarate, and ammonia, and the ratio of oxidized to reduced coenzymes.
Specific amounts of guanosine triphosphate (GTP) and adenosine diphosphate (ADP) also impact these reactions.
Ammonia transport to the liver involves Glutamine formation from glutamate in tissues. Glutamine and alanine are transported to the liver, where glutaminase releases ammonia. The liver uses this ammonia in the urea cycle. This occurs in most tissues.
The urea cycle's nitrogen atoms come from ammonia and aspartate.
The urea cycle's carbon and oxygen atoms come from CO₂.
The urea cycle is regulated by substrate availability.
CPS I can be activated allosterically by n-acetylglutamate.
N-acetylglutamate is synthesized from glutamate and acetyl-CoA.
Amino-acid breakdown increases glutamate concentration, stimulating N-acetylglutamate synthesis, thus increasing CPS I activity.
Amino acids can be divided into two groups based on their catabolic pathways: glucogenic and ketogenic.
Glucogenic amino acids are degraded to glucose precursors (pyruvate, α-ketoglutarate, succinyl-CoA, fumarate, and oxaloacetate).
Ketogenic amino acids are degraded to acetyl-CoA or acetoacetate.
Nonessential amino acids are synthesized from common metabolites (pyruvate, oxaloacetate, α-ketoglutarate, and 3 phosphoglycerate).
Tyrosine is synthesized from phenylalanine.
Essential amino acids cannot be synthesized in sufficient quantities for growth and maintenance and thus are required in the diet.
The essential amino acids are phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, histidine, arginine, leucine, and lysine.

Additional Information

Ammonia, urea, and uric acid are forms of nitrogen excretion.
The urea cycle has five main steps, involving the formation of carbamoyl phosphate, citrulline, argininosuccinate, fumarate, and arginine to finally yield urea as a product, along with other byproducts.

Synthesis of Amino Acids

Nonessential amino acids are synthesized from common metabolites like pyruvate, oxaloacetate, α-ketoglutarate, and 3-phosphoglycerate.
Tyrosine is synthesized by the hydroxylation of phenylalanine, an essential amino acid.

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Description

Test your knowledge on key concepts in amino acid metabolism with this quiz focused on glutamate dehydrogenase, the urea cycle, and metabolic intermediates. Explore how various conditions and coenzymes affect amino acid synthesis and degradation. Perfect for biochemistry students seeking to solidify their understanding of these essential biochemical processes.