Podcast
Questions and Answers
Which pancreatic enzyme hydrolyzes peptide bonds of aromatic amino acids?
Which pancreatic enzyme hydrolyzes peptide bonds of aromatic amino acids?
What is the process by which di- and tri-peptides are taken up into intestinal mucosa?
What is the process by which di- and tri-peptides are taken up into intestinal mucosa?
What is the role of α-ketoglutarate in amino acid metabolism?
What is the role of α-ketoglutarate in amino acid metabolism?
Which two amino acids do not participate in transamination?
Which two amino acids do not participate in transamination?
Signup and view all the answers
What is the fate of absorbed amino acids in the anabolic pathway?
What is the fate of absorbed amino acids in the anabolic pathway?
Signup and view all the answers
What is the primary function of carboxypeptidase?
What is the primary function of carboxypeptidase?
Signup and view all the answers
What is the coenzyme required for all transamination reactions?
What is the coenzyme required for all transamination reactions?
Signup and view all the answers
What is the outcome of the removal of amino group from amino acids?
What is the outcome of the removal of amino group from amino acids?
Signup and view all the answers
What is the enzyme responsible for oxidative deamination?
What is the enzyme responsible for oxidative deamination?
Signup and view all the answers
What is the byproduct of oxidative deamination?
What is the byproduct of oxidative deamination?
Signup and view all the answers
Which enzyme has autocatalytic activity and activates the remaining amount of trypsinogen and other pancreatic zymogens?
Which enzyme has autocatalytic activity and activates the remaining amount of trypsinogen and other pancreatic zymogens?
Signup and view all the answers
What is the primary function of elastase?
What is the primary function of elastase?
Signup and view all the answers
What is the purpose of glutamine synthetase?
What is the purpose of glutamine synthetase?
Signup and view all the answers
What is the result of the complete oxidation of α-keto acids?
What is the result of the complete oxidation of α-keto acids?
Signup and view all the answers
Which enzyme cleaves glutamine into glutamate and free ammonia?
Which enzyme cleaves glutamine into glutamate and free ammonia?
Signup and view all the answers
What is the significance of elevated plasma AST and ALT levels?
What is the significance of elevated plasma AST and ALT levels?
Signup and view all the answers
What is the primary function of enteropeptidase in the digestion of dietary proteins?
What is the primary function of enteropeptidase in the digestion of dietary proteins?
Signup and view all the answers
What is the pH range at which pepsin is most active?
What is the pH range at which pepsin is most active?
Signup and view all the answers
What is the term used to describe the process of constant synthesis and degradation of proteins in the body?
What is the term used to describe the process of constant synthesis and degradation of proteins in the body?
Signup and view all the answers
What is the primary characteristic of High Biological Value (HBV) proteins?
What is the primary characteristic of High Biological Value (HBV) proteins?
Signup and view all the answers
Which of the following is an example of a Low Biological Value (LBV) protein?
Which of the following is an example of a Low Biological Value (LBV) protein?
Signup and view all the answers
What is the estimated amount of body protein that is hydrolyzed and re-synthesized daily?
What is the estimated amount of body protein that is hydrolyzed and re-synthesized daily?
Signup and view all the answers
What is the function of bicarbonate in the pancreatic juice?
What is the function of bicarbonate in the pancreatic juice?
Signup and view all the answers
What is the term used to describe proteins that are found in animal sources such as meat, poultry, and seafood?
What is the term used to describe proteins that are found in animal sources such as meat, poultry, and seafood?
Signup and view all the answers
Study Notes
Protein Metabolism
- Proteins are large, complex molecules that play critical roles in the body.
- There are 20 amino acids that occur in mammalian proteins.
- Amino acids are the fundamental units of proteins.
Types of Proteins
- High Biological Value (HBV) proteins:
- Provide all essential amino acids.
- Also known as complete proteins.
- Found in animal sources (meat, poultry, seafood, milk, and cheese) and plant sources (soya beans).
- Low Biological Value (LBV) proteins:
- Lack one or more essential amino acids.
- Also known as incomplete proteins.
- Found in plant sources (cereals, legumes, and nuts), except for soya beans.
Protein Turnover
- Proteins in the body are constantly synthesized and degraded.
- This process, called protein turnover, leads to the hydrolysis and re-synthesis of 300-400 gm of body protein each day.
- In healthy adults, the total amount of protein in the body remains constant.
Digestion of Dietary Proteins
- In the stomach:
- HCl initiates the activation of pepsinogen into active pepsin.
- Pepsin is an endopeptidase with an optimum pH of 1-2.
- In the intestine:
- Pancreatic juice rich in bicarbonate neutralizes gastric secretion.
- Pancreatic zymogens are released, including trypsinogen, chymotrypsinogen, pro-carboxypeptidase, and pro-elastase.
- Enteropeptidase initiates activation of trypsinogen into active trypsin.
- Active trypsin has autocatalytic activity, activating the remaining pancreatic zymogens.
Pancreatic Enzymes
- Trypsin: an endopeptidase that hydrolyzes peptide bonds of basic amino acids (e.g., lysine and arginine).
- Chymotrypsin: an endopeptidase that hydrolyzes peptide bonds of aromatic amino acids.
- Carboxypeptidase: an exopeptidase that hydrolyzes peptide bonds adjacent to the free COOH group of the polypeptide chain.
- Elastase: an endopeptidase that hydrolyzes peptide bonds of small amino acids (e.g., glycine, alanine, and serine).
Absorption of Proteins
- Free amino acids are taken into intestinal mucosa by sodium-dependent active transport through Na+-dependent co-transporters.
- Di- and tri-peptides are taken up by a H+-linked transport system and hydrolyzed in the cytosol to amino acids.
Fate of Absorbed Amino Acids
Anabolic Pathways
- Synthesis of proteins: tissue proteins, enzymes, and hormones.
- Synthesis of specialized products (e.g., creatine, choline, nitrogen bases of nucleic acids).
- Synthesis of small peptides (e.g., glutathione).
Catabolic Pathways
- Removal of amino group (NH2) from amino acids by transamination and deamination processes.
- The resulting products are ammonia, urea, and α-keto acids.
- α-Keto acids are further metabolized to be completely oxidized into CO2, H2O, or converted into glucose or ketones.
Removal of Nitrogen from Amino Acids
- Removing the amino group is essential to produce energy from amino acids.
- The nitrogen can be incorporated into other compounds or excreted, with the carbon skeletons being metabolized.
Transamination
- α-Ketoglutarate plays an essential role in amino acid metabolism by accepting the amino groups from most amino acids, thus becoming glutamate.
- Glutamate produced by transamination can be oxidatively deaminated or used as an amino group donor in the synthesis of nonessential amino acids.
- All amino acids, except lysine and threonine, participate in transamination.
- All transamination reactions are reversible.
- Pyridoxal phosphate (PLP) is a coenzyme in all transamination reactions.
Oxidative Deamination
- Oxidative deamination is catalyzed by Glutamate dehydrogenase.
- It results in the liberation of the amino group as free ammonia (NH3).
- These reactions occur primarily in the liver and kidney.
Diagnostic Importance of Plasma Aminotransferases
- Elevated plasma levels of ALT and AST indicate damage to cells rich in these enzymes.
- Liver disease: Plasma AST and ALT are elevated, with ALT being more specific than AST for liver disease.
- Myocardial infarction and muscle disorders: Elevated AST only, with normal ALT plasma levels.
Transport of NH3 to the Liver
- Glutamine synthetase combines ammonia (NH3) with glutamate to form glutamine (a nontoxic transport form of ammonia).
- Glutamine is transported in the blood to the liver, where it is cleaved by glutaminase to produce glutamate and free ammonia.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
This quiz covers the basics of protein metabolism, including the structure and function of proteins, amino acids, and types of proteins.
