Protein Metabolism Lesson 2: Removal of Nitrogen

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Questions and Answers

What is the primary enzyme responsible for Type II Oxidative Deamination?

Aminotransferase

L-amino acid oxidase

L-a.a oxidase (correct)

D-amino acid oxidase

Which coenzyme is required for Type III Oxidative Deamination?

Coenzyme A

FAD (correct)

FMN

NADH

What is the biological importance of D-amino acids?

They are effectively metabolized by the liver. (correct)

They are synthesized in mammalian proteins.

They are abundant in animal cell membranes.

They are primarily found in human muscle tissue.

Which statement accurately describes Type II Oxidative Deamination?

It produces L-keto acids from L-amino acids. Signup and view all the answers

What is a characteristic of Non-Oxidative Deamination?

It includes both dehydration and hydrolytic types. Signup and view all the answers

What is the first step in amino acid catabolism?

Removal of the -Amino group Signup and view all the answers

What form is nitrogen removed from amino acids during catabolism?

Ammonia Signup and view all the answers

Which amino acids do not undergo transamination?

Threonine and Lysine Signup and view all the answers

Which type of deamination involves the removal of an amino group in the form of ammonia?

Oxidative Deamination Signup and view all the answers

What is the main purpose of nitrogen removal in amino acid metabolism?

Synthesis of glucose and fatty acids Signup and view all the answers

What type of reaction is transamination?

Reversible reaction Signup and view all the answers

Which enzyme catalyzes transamination reactions?

Transaminase Signup and view all the answers

Which statement about amino acid reactions is true?

All amino acid reactions require PLP Signup and view all the answers

What coenzyme is required for transaminase activity?

Pyridoxal Phosphate Signup and view all the answers

Which amino acid is the main acceptor of amino groups in transamination reactions?

Glutamate Signup and view all the answers

What is the primary role of glutamine under conditions of starvation?

To act as an amine group donor for synthesizing various molecules Signup and view all the answers

Which of the following statements about transamination reactions is true?

Amino acids are amino group donors. Signup and view all the answers

Which enzyme is also known as Glutamate Pyruvate Transaminase?

Alanine Transaminase (ALT) Signup and view all the answers

Which amino acid comprises approximately 7-10% of muscle protein content?

Alanine Signup and view all the answers

What is the most frequently used -keto acid in transamination reactions?

-Ketoglutarate Signup and view all the answers

What is the main function of alanine released from muscles during the post-absorptive state?

To facilitate the transport of ammonia to the liver Signup and view all the answers

Which pathway detoxifies ammonia into non-toxic urea?

Urea cycle Signup and view all the answers

What can glutamate produced by transamination reactions easily be converted to?

Ammonia Signup and view all the answers

An increase in ALT or AST in blood can indicate which of the following?

Liver disease Signup and view all the answers

Where does the urea cycle begin and end within the cells?

Begins in mitochondria and ends in the cytosol Signup and view all the answers

In the context of muscle amino acids released, what percentage of the total amino acids is glutamine?

25% Signup and view all the answers

Which of the following is NOT a product of transamination reactions?

Fatty acids Signup and view all the answers

What is the primary site of the urea cycle?

Liver Signup and view all the answers

What role does glutamine play in transporting ammonia?

It serves as a vehicle for transporting ammonia to the gut and kidneys Signup and view all the answers

What is the primary function of the Urea Cycle?

To detoxify and dispose of ammonia Signup and view all the answers

How is Aspartate regenerated in the Urea Cycle?

From Fumarate via transamination Signup and view all the answers

What percentage of nitrogen is excreted as Urea?

80-90% Signup and view all the answers

What occurs to blood urea nitrogen levels in hepatic failure?

They decrease Signup and view all the answers

What is the fate of Urea in the kidney?

It is excreted in urine Signup and view all the answers

Which condition indicates a problem with the Urea Cycle?

Hyperammonemia Signup and view all the answers

Which compound is NOT primarily a product of nitrogen excretion?

Glucose Signup and view all the answers

What role does Urease play in the intestine?

It converts Urea into ammonia and CO2 Signup and view all the answers

Study Notes

Removal of Nitrogen

Metabolism of amino acids involves both anabolism and catabolism.
First step in amino acid catabolism is nitrogen removal (amino group).
Nitrogen is removed as ammonia, producing an α-keto acid (carbon skeleton).

Pathways for Nitrogen Removal

Nitrogen removal occurs through:
- Transamination: Transfer of amino group from amino acid to α-keto acid, producing a new α-keto acid and amino acid, with no free ammonia formed.
- Deamination: Removal of amino group as ammonia; can be oxidative or non-oxidative.
- Trans-deamination: Combination of transamination and deamination.

Transamination

All amino acids except threonine and lysine undergo transamination.
Catalyzed by transaminase (aminotransferase), which is specific to amino acid donors.
Requires pyridoxal phosphate (PLP), the active form of Vitamin B6.

Examples of Transamination Reactions

Alanine transaminase (ALT): Alanine + α-ketoglutarate → Pyruvate + Glutamate.
Aspartate transaminase (AST): Aspartate + α-ketoglutarate → Oxaloacetate + Glutamate.
Glutamate can be easily deaminated or used for synthesizing non-essential amino acids.

Biological Importance of Transamination

α-Ketoglutarate is the most commonly used keto acid.
Transamination reactions convert amino acids to their respective α-keto acids, which can enter metabolic pathways like gluconeogenesis or the TCA cycle.

Medical Importance of Transaminases

ALT and AST serve as biomarkers for liver diseases; elevated levels in blood indicate possible damage.

Oxidative Deamination

L-amino acid oxidase converts L-amino acids to their corresponding α-keto acids, releasing ammonia; requires FMN as a coenzyme.
D-amino acid oxidase metabolizes D-amino acids similarly but uses FAD; D-amino acids are typically not part of mammalian proteins.

Non-Oxidative Deamination

Non-oxidative deamination occurs without oxidation, including dehydration and hydrolytic types.
Glutamine (Gln) serves as a vehicle for ammonia transport from muscle to liver and gut.

Ammonia Transport and Urea Cycle

Urea cycle detoxifies ammonia to urea, occurring primarily in the liver within periportal hepatocytes, involving both mitochondria and cytosol.
Urea is the main excretion compound, eliminating 80-90% of nitrogen, alongside smaller percentages from creatinine, NH4+, and uric acid.

Blood Levels and Clinical Significance

Normal blood urea nitrogen (BUN) ranges from 7-18 mg/dl.
Urea production decreases with hepatic failure and increases with amino acid catabolism and renal insufficiency.

Hyperammonemia

Elevated ammonia levels in blood, known as hyperammonemia or ammonia intoxication, result from urea cycle disorders or liver dysfunction.

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Description

This quiz covers the critical topic of nitrogen removal in amino acid metabolism, focusing on both anabolism and catabolism. Understanding these processes is essential for grasping how amino acids are utilized and degraded in the body. Test your knowledge on the steps and significance of nitrogen removal in protein metabolism.