Proteins and Their Digestion
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Proteins and Their Digestion

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Questions and Answers

What percentage of protein is nitrogen (N)?

  • 20%
  • 12%
  • 24%
  • 16% (correct)

    • Proteins are synthesized from 22 different amino acids.

    False

    What are the three phases of protein digestion?

    Gastric digestion, digestion by pancreatic proteases, and digestion at the brush border.

    ____ is the enzyme activated from pepsinogen that cleaves dietary proteins in the stomach.

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

    Match the following phases of protein digestion with their description:

    <p>Phase 1 = Gastric digestion Phase 2 = Digestion by pancreatic proteases Phase 3 = Digestion at the brush border</p> Signup and view all the answers

    Which of the following statements about amino acids is correct?

    <p>Amino acids are the building blocks of proteins.</p> Signup and view all the answers

    Gastric acid aids in protein digestion by denaturing proteins.

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

    Name a potential role of glutamine and glutamate mentioned in the context of human milk.

    <p>Protection against neonatal allergies and infections.</p> Signup and view all the answers

    What is the relationship between amino acid rates and body protein concentration?

    <p>Amino acid rates are divided by the concentration of amino acid in body protein.</p> Signup and view all the answers

    High protein intake is beneficial for individuals with renal failure.

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

    What happens to body protein during disease states such as infection or trauma?

    <p>Body protein is mobilized for use as fuel and for gluconeogenesis.</p> Signup and view all the answers

    In the fed state, dietary intake of amino acids and glucose is used to replete ___ and ___ lost during the postabsorptive period.

    <p>protein, glycogen</p> Signup and view all the answers

    Match the amino acids with their respective roles:

    <p>Glutamine = Fuel for gut cells and synthesis of nucleotides Arginine = Precursor of nitric oxide, important for immunity &amp; healing Leucine = A component involved in protein synthesis Methionine = Essential amino acid for metabolic functions</p> Signup and view all the answers

    What is the primary role of the pyloric sphincter in digestion?

    <p>To regulate the passage of food into the duodenum</p> Signup and view all the answers

    Pancreatic proteases are activated in the stomach.

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

    What enzyme activates trypsinogen into trypsin?

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

    The secretion known as ______ stimulates the release of pancreatic enzymes.

    <p>CCK-PZ</p> Signup and view all the answers

    Match the following components with their functions:

    <p>Trypsinogen = Inactive precursor of a protease Enteropeptidase = Activates trypsinogen CCK-PZ = Stimulates digestive enzyme release HCO3- = Neutralizes gastric acid</p> Signup and view all the answers

    What does trypsin specifically target?

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

    Duodenal cells contribute to the digestion process by secreting hormones.

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

    Which cells in the pancreas secrete digestive enzymes?

    <p>Pancreatic Acinar Cells</p> Signup and view all the answers

    ______ is the process by which trypsinogen is converted into trypsin.

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

    What is the purpose of bicarbonate secretion in the duodenum?

    <p>To neutralize gastric acid</p> Signup and view all the answers

    Which enzyme is involved in the autocatalysis process to activate trypsinogen?

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

    Chymotrypsinogen is directly activated by CCK-PZ.

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

    What is the role of bicarbonate (HCO3-) in the digestive process?

    <p>Neutralizes acid</p> Signup and view all the answers

    Trypsinogen is converted to _______ by enteropeptidase.

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

    Match the pancreatic enzymes with their respective proenzymes:

    <p>Trypsin = Trypsinogen Chymotrypsin = Chymotrypsinogen Elastase = Proelastase Carboxypeptidase = Procarboxypeptidase</p> Signup and view all the answers

    Which of the following is a product of pancreatic protease action?

    <p>Free amino acids</p> Signup and view all the answers

    Brush border endopeptidases are not involved in protein digestion.

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

    What initiates the secretion of pancreatic enzymes?

    <p>Presence of food in the duodenum</p> Signup and view all the answers

    The __________ cells in the pancreas are responsible for secreting bicarbonate.

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

    Which substance is secreted by endocrine cells in response to food in the duodenum?

    <p>CCK-PZ</p> Signup and view all the answers

    What type of transport is involved in the absorption of amino acids in the intestinal epithelium?

    <p>Na+-dependent co-transport</p> Signup and view all the answers

    Proteins in the body are in a constant state of synthesis and breakdown, known as turnover.

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

    What are the two types of isotopes used in tracer methods for amino acid kinetics?

    <p>Radioactive isotopes and stable isotopes</p> Signup and view all the answers

    The ________ of proteins depends on the type of protein.

    <p>turnover rate</p> Signup and view all the answers

    Match the amino acids with their corresponding metabolic pathways:

    <p>Glutamate = Amino acid synthesis Alanine = Amino transfer Aspartate = Amino transfer Alpha-ketoglutarate = Keto acid metabolism</p> Signup and view all the answers

    Which enzyme is primarily involved in the amino transfer for the synthesis of glutamate?

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

    Di- and tripeptides are completely absorbed in the intestinal lumen without the need for enzymatic digestion.

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

    What measurement method involves using isotopically labeled tracers?

    <p>Tracer methods</p> Signup and view all the answers

    Amino acids and dipeptides enter the epithelium through __________ membranes.

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

    In a healthy adult with stable weight, there is a balance between which two processes?

    <p>Synthesis and breakdown</p> Signup and view all the answers

    Study Notes

    Proteins

    • 16% Nitrogen
    • Made up of 20 amino acids
    • Important for:
      • Blood stability
      • Muscle
      • Centers for biochemical reactions
      • Signaling (hormones and cytokines)
      • Enzymes

    Protein Digestion

    • Phase 1 - Gastric digestion
      • Pepsinogen is activated to pepsin via autoactivation and autocatalysis
      • Pepsin cleaves proteins in stomach
      • Large peptide fragments and free amino acids are passed to the duodenum
    • Phase 2 - Digestion by pancreatic enzymes
      • Trypsinogen is converted to Trypsin via enteropeptidase
      • Trypsin activates other pancreatic enzymes:
        • Chymotrypsinogen
        • Proelastase
        • Procarboxypeptidases
      • Pancreatic enzymes breakdown proteins into smaller peptides
    • Phase 3 - Digestion of peptides at the brush border
      • Dipeptidases and tripeptidases breakdown peptides at the brush border
      • Amino acids, dipeptides, and tripeptides are absorbed into the intestinal epithelium
    • Phase 4 - Absorption
      • Free amino acids are transporter into the bloodstream via Na+ dependent co-transport
      • Dipeptides and tripeptides are transported into bloodstream via facilitated diffusion

    Amino Acid Metabolism

    • Amino acids are metabolized via several pathways
    • Some amino acids are used as a carbon source for gluconeogenesis
    • Alanine and Glutamate can carry amino groups to the liver
    • Glutamate is important in the urea cycle

    Protein Turnover Rates

    • Proteins are constantly being synthesized and degraded: Turnover
    • Turnover rates vary depending on the protein
      • High turnover rate: Proteins with regulated concentrations or that act as signals
      • Low turnover rate: Structural proteins
    • In healthy individuals with stable weight: a balance exists between protein breakdown and synthesis
      • Nitrogen (N)-balance

    Measuring Protein Turnover

    • Nitrogen Balance: Measuring N intake and loss
    • Tracer methods
      • Isotopically labeled tracers: Radioactive or stable isotopes are used to track amino acid kinetics
      • Ex: L-[1-13C]leucine tracer - allows for measuring whole body protein kinetics

    Protein Requirements

    • Classical N balance studies are used to measure protein requirements, it can take 7-10 days to reach a steady state in urinary N output.
    • Indicator tracer methods can be used to measure protein oxidation directly, without days of equilibration.

    Protein in Disease

    • In disease (infection, burn, surgery, trauma): Metabolic rate rises and protein is mobilized for fuel and gluconeogenesis.
    • Significant protein loss can be seen in elderly and chronically ill.
    • Supplemental nutrients can help blunt, but not reverse protein loss in disease
      • Insulin and growth hormone can improve protein synthesis
      • Specific amino acids:
        • Glutamine: important for gut cells and nucleotide synthesis
        • Arginine: precursor of nitric oxide, important for healing and immunity

    Protein Controversies

    • High protein intake and renal failure
    • High protein diets for weight loss
    • Protein intake and bone health

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    Description

    Explore the essential role of proteins in the body and the detailed phases of protein digestion. Understand the process from gastric digestion to the absorption of amino acids in the intestines. This quiz covers important enzymes and functions of proteins in various biological processes.

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