Protein Digestion and Absorption

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Questions and Answers

What is the enzyme responsible for converting γ-glutamyl-cysteine to cysteine?

  • Dipeptidase
  • γ-Glutamyl cyclotransferase
  • Glutathione synthetase
  • γ-Glutamylcysteine synthetase (correct)

What is the consequence of a deficiency in glutathione synthetase enzyme?

  • Increased levels of 5-oxoproline in blood and urine (correct)
  • Decreased levels of 5-oxoproline in blood and urine
  • Impaired absorption of amino acids
  • Enhanced synthesis of non-essential amino acids

What is the role of γ-glutamyl transpeptidase in the γ-glutamyl cycle?

  • To convert cysteine to γ-glutamyl-cysteine
  • To transfer γ-glutamyl group from glutathione to an amino acid (correct)
  • To catalyze the formation of glutathione
  • To break down dietary proteins into amino acids

What is the function of pepsinogen in protein digestion?

<p>To convert into active enzyme (C)</p> Signup and view all the answers

What is the source of amino acids in the amino acid pool?

<p>Both dietary proteins and non-essential amino acids synthesized in the body (C)</p> Signup and view all the answers

What is the byproduct of the reaction catalyzed by oxoprolinase?

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

How are amino acids absorbed from the small intestine?

<p>Through active transport mechanism using a carrier protein (B)</p> Signup and view all the answers

What is the energy source for the sodium-amino acid carrier system?

<p>Energy from Na/K+ pump (D)</p> Signup and view all the answers

What is the function of the Na/K+ pump in amino acid absorption?

<p>To pump sodium out of the cell (C)</p> Signup and view all the answers

Where are amino acids absorbed from in the digestive system?

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

What is the result of protein digestion in the stomach?

<p>Large peptides and some free amino acids (A)</p> Signup and view all the answers

What is the primary fate of the products resulting from deamination?

<p>Excretion in urine (C)</p> Signup and view all the answers

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

<p>To transfer the amino group from one amino acid to another (D)</p> Signup and view all the answers

What is the byproduct of oxidative deamination reactions?

<p>Ammonia and alpha-keto acid (D)</p> Signup and view all the answers

What is the purpose of the catabolic pathway of amino acids?

<p>To break down amino acids into energy (A)</p> Signup and view all the answers

Which of the following compounds is involved in transamination reactions?

<p>Alpha-ketoglutarate (C)</p> Signup and view all the answers

What is the primary function of the amino acid pool?

<p>To provide a source of amino acids for various bodily functions (B)</p> Signup and view all the answers

What is the byproduct of the transamination reaction between glutamic acid and pyruvic acid?

<p>α- keto glutarate (A)</p> Signup and view all the answers

Which enzyme catalyzes the transamination reaction between glutamic acid and oxaloacetic acid?

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

What is the diagnostic value of transaminases in the blood?

<p>They are normally intracellular enzymes and elevated levels indicate cell damage (D)</p> Signup and view all the answers

What does an increase in the level of both ALT and AST indicate?

<p>Damage to liver cells (A)</p> Signup and view all the answers

What does an increase in the level of AST alone suggest?

<p>Damage to heart muscle, skeletal muscle, or kidney cells (D)</p> Signup and view all the answers

Flashcards

Essential amino acids

Amino acids that cannot be synthesized by the body and must be obtained from the diet.

Non-essential amino acids

Amino acids that can be synthesized by the body, often from other amino acids.

Amino acid catabolism

The breakdown of amino acids.

Deamination

The removal of the amino group (-NH2) from an amino acid.

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Oxidative deamination

Deamination that involves the oxidation of the amino acid, producing an α-keto acid and ammonia.

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Transamination

Deamination that involves the transfer of an amino group from one amino acid to another, forming a new amino acid and a new α-keto acid.

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Transdeamination

A combination of oxidative deamination and transamination, resulting in the removal of an amino group and the formation of an α-keto acid and ammonia.

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Amino acid absorption

The absorption of amino acids from the small intestine into the bloodstream.

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Carrier protein transport system

A transport mechanism that moves amino acids across cell membranes using energy from the Na+/K+ pump.

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Glutathione transport system

An active transport system involving glutathione, a tripeptide critical for amino acid absorption.

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Oxoprolinuria

An inherited disorder where a deficiency in glutathione synthetase leads to accumulation of 5-oxoproline, causing acidosis and neurological damage.

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Protein digestion

The breakdown of proteins into smaller peptides and amino acids in the digestive system.

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Protein denaturation

Proteins are unfolded by gastric HCl, exposing their peptide bonds for easier digestion.

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Pepsin

A protein that breaks down proteins into peptides and amino acids in the stomach.

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Transaminases

Enzymes that catalyze the transfer of an amino group from one amino acid to another.

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Alanine transaminase (ALT)

A transaminase that converts glutamic acid and pyruvic acid into alanine and α-keto glutarate.

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Aspartate transaminase (AST)

A transaminase that converts glutamic acid and oxaloacetic acid into aspartic acid and α-keto glutarate.

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Elevated transaminases

Elevated levels of transaminases in the blood indicate damage to cells that produce these enzymes, such as liver cells.

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Amino acid transport to the liver

The process of transporting absorbed amino acids from the small intestine to the liver via the portal blood.

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Amino acid pool

The pool of amino acids available for use in the body.

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Study Notes

Amino Acid Pool and Catabolism

  • Amino acids can be categorized into essential and non-essential amino acids
  • Non-essential amino acids can be synthesized in the body
  • Catabolism of amino acids occurs through deamination, which involves the removal of the amino group
  • Deamination can occur through oxidative deamination, transamination, or transdeamination
  • Oxidative deamination involves the oxidation and deamination of amino acids to form α-keto acids and ammonia
  • Transamination involves the transfer of an amino group from one α-amino acid to an α-keto acid to form a new α-amino acid and a new α-keto acid
  • Transdeamination involves the removal of the amino group from an amino acid to form an α-keto acid and ammonia

Amino Acid Absorption

  • Amino acids are absorbed from the small intestine through passive and active transport mechanisms
  • The carrier protein transport system (sodium-amino acid carrier system) is an active transport mechanism that uses energy from the Na+/K+ pump
  • The glutathione transport system (γ-glutamyl cycle) is another active transport mechanism
  • Oxoprolinuria is an inherited disorder caused by a deficiency of glutathione synthetase, leading to increased levels of 5-oxoproline in the blood and urine, acidosis, and neurological damage

Protein Digestion and Absorption

  • Proteins are denatured by gastric HCl and then broken down into large peptides and some free amino acids by pepsin
  • Large peptides are further broken down into smaller peptides and free amino acids
  • Amino acids are absorbed from the small intestine through passive and active transport mechanisms
  • The absorbed amino acids are transported to the liver through the portal blood

Transamination and Transaminases

  • Transaminases are enzymes that catalyze the transfer of an amino group from an α-amino acid to an α-keto acid
  • Examples of transaminases include alanine transaminase (ALT) and aspartate transaminase (AST)
  • ALT catalyzes the reaction between glutamic acid and pyruvic acid to form alanine and α-keto glutarate
  • AST catalyzes the reaction between glutamic acid and oxaloacetic acid to form aspartic acid and α-keto glutarate
  • Transaminases are elevated in the blood when there is damage to cells that produce these enzymes, such as liver cells, heart muscle cells, or skeletal muscle cells

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