Questions and Answers
What is the major proteolytic enzyme in the stomach?
What activates pepsinogen in the stomach?
Which pancreatic enzyme cleaves specifically at the C-terminal of arginine or lysine?
What results from a deficiency in pancreatic secretion?
Signup and view all the answers
Which enzyme converts pancreatic trypsinogen to trypsin?
Signup and view all the answers
What is the role of aminopeptidase in protein digestion?
Signup and view all the answers
What type of protein digestion abnormalities can occur due to surgical removal of the pancreas?
Signup and view all the answers
What is produced when oligopeptides are digested by enzymes on the intestinal surface?
Signup and view all the answers
What primarily causes elevated serum bilirubin levels?
Signup and view all the answers
Which amino acid undergoes rapid oxidative deamination by glutamate dehydrogenase?
Signup and view all the answers
Which coenzyme is primarily used for oxidative deamination by glutamate dehydrogenase?
Signup and view all the answers
What role does glutamine synthetase play in ammonia transport?
Signup and view all the answers
What stimulates glutamate dehydrogenase activity after protein ingestion?
Signup and view all the answers
Which compound is produced from glutamine in the liver?
Signup and view all the answers
What process does alanine aminotransferase primarily facilitate?
Signup and view all the answers
Which two factors regulate the direction of the reaction facilitated by glutamate dehydrogenase?
Signup and view all the answers
What can cause hyperammonemia?
Signup and view all the answers
What is the most common hereditary cause of hyperammonemia?
Signup and view all the answers
What is a major neurotoxic effect of high ammonia levels in the blood?
Signup and view all the answers
Which dietary change can help manage hyperammonemia?
Signup and view all the answers
What is the role of phenylbutyrate in treating hyperammonemia?
Signup and view all the answers
What is the primary function of aminotransferases?
Signup and view all the answers
Which amino acids do not participate in transamination?
Signup and view all the answers
What coenzyme do aminotransferases require for their function?
Signup and view all the answers
What does elevated plasma levels of aminotransferases indicate?
Signup and view all the answers
Which aminotransferase transfers amino groups from glutamate to oxaloacetate?
Signup and view all the answers
What is a key result of the reaction catalyzed by alanine aminotransferase (ALT)?
Signup and view all the answers
Aminotransferases are primarily located in which part of the body?
Signup and view all the answers
Which condition is most likely to cause high levels of AST and ALT in plasma?
Signup and view all the answers
What is indicated by a positive nitrogen balance?
Signup and view all the answers
Which protein is more likely to have a longer half-life based on its N-terminal residue?
Signup and view all the answers
What primarily regulates protein turnover in cells?
Signup and view all the answers
What are the two enzyme systems involved in protein degradation?
Signup and view all the answers
Which condition can result in negative nitrogen balance?
Signup and view all the answers
What does a steady state of the amino acid pool imply?
Signup and view all the answers
What type of proteins are generally more stable and have a longer lifespan?
Signup and view all the answers
Which of the following can lead to increased protein catabolism?
Signup and view all the answers
Study Notes
Protein Turnover
- Steady state of amino acid pool maintained (input = output).
- Constant degradation and synthesis of proteins regulated by cellular concentration.
- Approximately 300-400g of proteins are hydrolyzed and resynthesized daily.
- Protein turnover varies by lifespan:
- Short-lived: regulatory/misfolded proteins.
- Long-lived: most tissue proteins.
- Structurally stable: collagen.
Nitrogen Balance
- Occurs when nitrogen intake equals nitrogen output.
- Positive Nitrogen Balance: more intake than output, indicating tissue growth.
- Common during growth, pregnancy, muscular training, and prolonged positive nitrogen balance.
- Negative Nitrogen Balance: output exceeds intake, leading to potential health issues.
- Consequences include starvation, malnutrition, chronic diseases, and increased catabolism.
Protein Metabolism
- Degradation via two systems:
- Energy-dependent ubiquitin-proteasome mechanism for endogenous proteins.
- Non-energy-dependent lysosomes for extracellular proteins.
- Proteins with specific N-terminal residues influence their half-life.
- Serine at N-terminal: long half-life (>20h).
- Aspartate at N-terminal: short half-life (3min).
- PEST-rich sequences result in rapid degradation.
Digestion of Proteins
- Proteins are antigenic and lose this property upon digestion.
- In stomach:
- Gastric acid denatures proteins.
- Pepsin becomes active from pepsinogen through HCl, catalyzing protein cleavage.
- In small intestine:
- Pancreatic proteases cleave polypeptides into smaller units.
- Enteropeptidase activates trypsin, which catalyzes further proteolytic activity.
Abnormalities in Protein Digestion
- Deficiencies in pancreatic secretion lead to incomplete protein and fat digestion.
- Resulting conditions include steatorrhea (abnormal lipid appearance) and undigested protein in feces.
- Aminopeptidases in the intestine cleave N-terminal residues, producing free amino acids and smaller peptides.
Transamination
- Aminotransferases catalyze transfer of amino groups to carbon skeletons, predominantly in liver, kidney, intestine, and muscle.
- All amino acids except lysine and threonine participate in transamination.
- Lysine and threonine undergo deamination instead.
Aminotransferases
- Each aminotransferase has specific amino group donors.
- Examples:
- Alanine aminotransferase (ALT) transfers alanine's amino group to α-ketoglutarate, forming pyruvate and glutamate.
- Aspartate aminotransferase (AST) transfers from glutamate to oxaloacetate, forming aspartate.
Mechanism of Action of Aminotransferases
- Require pyridoxal phosphate as a coenzyme to transfer amino groups.
- Converts amino acid to aldehyde form, enabling subsequent reactions with α-keto acids.
Diagnostic Value of Plasma Aminotransferases
- Elevated aminotransferases indicate cellular damage, particularly in hepatic tissue.
- AST and ALT levels rise in liver diseases and conditions like myocardial infarction.
- Distinguish between hepatic and non-hepatic causes of elevation.
Glutamate Dehydrogenase
- Catalyzes oxidative deamination of glutamate, releasing free ammonia.
- Primarily active in liver and kidney, utilizing NAD or NADP.
- Regulation occurs through substrate concentration and coenzyme ratios.
Transport of Ammonia to Liver
- Two mechanisms for ammonia transport:
- Glutamine synthetase forms glutamine in most tissues, transported to the liver.
- Muscle utilizes transamination to form alanine, transported to liver for gluconeogenesis.
Hyperammonemia
- Result of compromised liver function or genetic defects in the urea cycle, leading to dangerous ammonia levels.
- Symptoms include neurotoxicity, tremors, slurred speech, and potential coma or death.
- Treatment involves dietary protein limitation and administration of compounds that facilitate nitrogen excretion (e.g., phenylbutyrate).
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Explore the concept of protein turnover and its regulation in this quiz. Learn about the constant processes of protein degradation and synthesis, and understand how these are influenced by protein concentrations within cells. Test your knowledge on the differences between short-lived and long-lived proteins.
