Amino Acid Metabolism and Protein Digestion

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Questions and Answers

Amino acids are primarily involved in the synthesis of carbohydrates and fats.

False (B)

What is the average protein turnover rate in a 70 kg man?

400 g per day

Which of the following amino acids are obtained from the diet?

  • Non-essential amino acids
  • Essential amino acids (correct)

Protein synthesis can occur even if the body is deficient in essential amino acids.

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

How is nitrogen balance maintained in the body?

<p>The rate of protein synthesis balances the rate of protein degradation.</p> Signup and view all the answers

What type of molecules are dietary proteins?

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

Dietary proteins are easily absorbed directly from the intestine.

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

What happens to dietary proteins during cooking?

<p>They are denatured.</p> Signup and view all the answers

What class of enzymes are proteolytic enzymes?

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

Proteolytic enzymes are secreted in their active form.

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

Which of the following is NOT an example of an endopeptidase?

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

Exopeptidases work by breaking peptide bonds at the ends of the polypeptide chain.

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

What is the name of the enzyme that acts on the peptide bond at the carboxyl terminal end of the polypeptide chain?

<p>Carboxypeptidase</p> Signup and view all the answers

Which cells in the stomach secrete hydrochloric acid?

<p>Chief cells</p> Signup and view all the answers

Hydrochloric acid denatures proteins by lowering the pH.

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

What is the inactive form of pepsin called?

<p>Pepsinogen</p> Signup and view all the answers

The conversion of pepsinogen to pepsin is triggered by the removal of ______ amino acids from the N-terminal end.

<p>44</p> Signup and view all the answers

What is the optimal pH for pepsin activity?

<p>around 2</p> Signup and view all the answers

Pepsin is a type of exopeptidase.

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

Which amino acids are involved in peptide bond hydrolysis by Pepsin?

<p>Phe, Tyr, Trp, Met (B)</p> Signup and view all the answers

What are the two end products of protein breakdown by Pepsin?

<p>Proteoses and peptones</p> Signup and view all the answers

Rennin is active in both infants and adults.

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

What is the name of the milk protein that is converted to paracasein by rennin?

<p>Casein</p> Signup and view all the answers

Pancreatic enzymes work optimally in an acidic environment.

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

What hormone stimulates the secretion of pancreatic juice?

<p>Cholecystokinin (CCK)</p> Signup and view all the answers

Which of the following is NOT an endopeptidase secreted by the pancreas?

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

Pancreatic enzymes are secreted in their active form.

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

What activates trypsinogen to trypsin?

<p>Enterokinase</p> Signup and view all the answers

Trypsin can activate other pancreatic enzymes.

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

What is the function of chymotrypsin in protein digestion?

<p>It hydrolyzes peptide bonds where the carboxyl group belongs to aromatic amino acids.</p> Signup and view all the answers

Chymotrypsin is secreted in its active form.

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

What is the optimal pH for the activity of chymotrypsin?

<p>7-8 (C)</p> Signup and view all the answers

What happens if trypsinogen is activated prematurely inside the pancreas?

<p>Acute pancreatitis</p> Signup and view all the answers

Elastase is a type of exopeptidase.

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

What is the inactive form of elastase called?

<p>Proelastase</p> Signup and view all the answers

Elastase primarily digests ______ and ______.

<p>elastin, collagen</p> Signup and view all the answers

Flashcards

Amino Acid Role

Amino acids are essential for synthesizing structural and functional proteins.

Protein Storage

The body does not store proteins; they are continuously synthesized and degraded.

Protein Turnover Rate

A 70 kg man has an average turnover rate of 400g of protein daily.

Essential Amino Acids

Amino acids that must be obtained from the diet; deficiency halts protein synthesis.

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Non-Essential Amino Acids

Amino acids made in the body or obtained from the diet; not necessary to eat.

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Dynamic Steady State

The amino acid pool maintains a balance of synthesis and degradation.

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Digestive Enzymes

Proteins must be digested into amino acids to be absorbed.

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Hydrolases

Enzymes that catalyze the hydrolysis of proteins; includes proteases.

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Endopeptidases

Enzymes that break peptide bonds within the protein chain.

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Exopeptidases

Enzymes that act on peptide bonds at the ends of polypeptides.

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Pepsin Activation

Pepsinogen is converted to pepsin by hydrochloric acid in the stomach.

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Pepsin Function

Pepsin hydrolyzes peptide bonds, breaking proteins into smaller units.

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Rennin

Also known as chymosin, it curdles milk in infants, not adults.

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Pancreatic Enzymes

Digestive enzymes secreted by the pancreas; work at pH 8.

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Trypsin Activation

Trypsinogen is activated by enterokinase in the intestine.

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Trypsin Function

Hydrolyzes peptide bonds of basic amino acids like arginine and lysine.

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Chymotrypsin Activation

Chymotrypsinogen is activated by trypsin to chymotrypsin.

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Chymotrypsin Function

Hydrolyzes peptide bonds involving aromatic amino acids.

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Elastase

Endopeptidase that digests elastin and collagen at pH 8.

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Acute Pancreatitis

Premature activation of trypsinogen leads to self-digestion of the pancreas.

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Proteolytic Enzymes

Enzymes that break down proteins into smaller peptides and amino acids.

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Cooking Proteins

Cooking denatures proteins, making them easier to digest.

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pH for Pepsin

Pepsin works best at a pH of around 2.

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Zymogens

Inactive forms of digestive enzymes, activated in the digestive tract.

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Carboxypeptidase

An exopeptidase that acts on carboxyl terminal ends of peptides.

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Aminopeptidase

An exopeptidase that acts on amino terminal ends of peptides.

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Digestive Sites

Protein digestion takes place in the stomach, pancreas, and intestines.

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Study Notes

Amino Acid Metabolism

  • Amino acids are crucial for building structural and functional proteins.
  • Humans don't store proteins, so synthesis and breakdown rates are balanced.
  • Essential amino acids must come from diet.
  • Non-essential amino acids can be made by the body or ingested.

Digestion and Absorption of Proteins

  • Dietary proteins are too large to be absorbed directly.
  • Digestion breaks them into smaller amino acids.
  • Hydrolases (class 3 enzymes) break down proteins in the digestive process.
  • Proteolytic enzymes are secreted in inactive forms (zymogens) and activated in the intestine.

Endopeptidases

  • These enzymes break peptide bonds within protein molecules.
  • Examples include pepsin, trypsin, chymotrypsin, and elastase.

Exopeptidases

  • They break peptide bonds at the ends of polypeptide chains.
  • Carboxypeptidase cleaves peptide bonds at the carboxyl end.
  • Aminopeptidase cleaves peptide bonds at the amino end.

Gastric Digestion

  • Hydrochloric acid is secreted to create optimal pH for pepsin.
  • Hydrochloric acid also denatures proteins.
  • Pepsin, an endopeptidase, breaks down proteins into proteoses and peptones.

Rennin (Chymosin)

  • Important in infants for curdling milk.
  • Rennin converts casein to paracasein.
  • This denatured protein is digestible by pepsin.

Pancreatic Digestion

  • Pancreatic enzymes function best at a pH of 8 (alkaline).
  • Pancreatic juice contains endopeptidases like trypsin, chymotrypsin, and elastase.
  • These work alongside carboxypeptidase.
  • Trypsinogen is activated to trypsin by enterokinase.

Trypsin

  • Trypsin activates other digestive enzymes.
  • It hydrolyzes peptide bonds involving basic amino acids.

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