L25-26: Protein and AA Metabolism I-II Flashcards
Describe protein digestion in the digestive tract
- Acidic pH of stomach denatures proteins - Pepsinogen is secreted by the stomach - It autoinhibits it’s active site, becomes altered in acidic environment and cleaves itself into pepsin - Pepsin’s active site contains aspartic acid residues. - It is a endopeptidase and cleaves internal peptide bonds, prefers bonds formed between AA groups of aromatic and hydrophobic amino acids - Chyme enters duodenum, stimulates release of secretin and CCK by intestinal mucosa - Secretin: stimulates acinar cells in pancreas = alkaline fluid released (bicarb rich), which neutralizes chym - CCK: stimulates release of bile and release of pancreatic digestive zymogens (trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidases) - Enteropeptidase present on wall of intestinal mucosa cleaves trypsinogen to trypsin - Trypsin cleaves remaining pancreatic zymogens into active forms (chymotrypsin, elastase, carboxypeptidases)
Function of pepsin
- Endopeptidase that prefers cleaving bonds formed bw aromatic and hydrophobic AA groups
List of pancreatic digestive enzymes
- trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidases
Function of trypsinogen
- Activating pancreatic digestive zymogens and also acting as a protease
Function of secretin
- neutralizes chyme for the purpose of allowing function of pancreatic digestive enzymes
Function of CCK
- stimulates release of digestive enzymes from pancreas - stimulates release of bile from GB
Where are secretin and CCK released from? What stimulates their release?
- intestinal mucosa cells - stimulated by chyme
Function of enteropeptidase. Where is it found?
- found on intestinal mucosa - cleaves trypsinogen to trypsin
What is the ratio of peptides to free amino acids that pancreatic proteases and peptidases?
- 60% peptides : 40% free amino acids
Describe transport of peptides and amino acids across the intestinal mucosa
- Pancreatic proteases and peptidases generate 60:40 ratio of peptides:free amino acids - Endopeptidases and aminopeptidases on luminal surface of epithelial of small intestine generate free AAs or di/tri peptides, which are absorbed via several transport systems - Specific AA transports require energy input often via secondary active transporters (coupled to sodium gradients) - Di/tri-peptide transport require energy input via proton gradients - Peptidases in epithelial cells hydrolyze di/tri peptides to free AAs - Free AAs exit across basal membrane into circulation via facilitated diffusion
Difference between AA and CHO transport across intestinal mucosa.
- CHO need to be in monosaccharide form in order to pass via specific receptors - AAs can be in free AA or di/tri peptide form in order to pass via specific receptors
What is acute pancreatitis? Symptoms? Causes? Triggers? Treatment?
- Inflammatory disease of pancreas caused by premature activation of pancreatic digestive zymogens - Symptoms = abdominal pain, vomiting - Causes = pancreatic necrosis - Triggers = alcohol, infections, gallstones - Treatment = supportive via analgesics, fasting, elemental jejunal tube or TPN
What is Hartnup disease? Symptoms? Treatment?
- Rare genetic disorder affecting transporter of large, neutral amino acid resulting in no absorption of these amino acids across intestinal epithelial cells, also in prox tubule of kidney causing elimination issue - Symptoms? Similar to pellagra, which is niacin deficiency – 4 D’s – diarrhea, dermatitis, dementia, death. - Treatment? Dietary supplementation with niacin
What is celiac disease? Cause? Result? Symptoms? Treatment?
- Inappropriate immune respone to alpha-gliadin, which is a glycoprotein found in wheat and other grains - Result? Reduction of absorptive area of small intestine, results in malabsorption - Symptoms? Abdominal cramps, bloating and malabsorptive symptoms - Treatment? Avoidance of alpha-gliadin containing foods
What is meant by term ‘amino acid pool’?
- Sum of intracellular and extracellular free AAs – ie. those not incorporated into proteins
What is meant by term nitrogen balance?
- Steady state condition whereby nitrogen content of diet equals excretion of nitrogenous waste products.
What is meant by term positive nitrogen balance? What does this lead to?
- Incorporation of dietary AAs into proteins exceeds protein breakdown - Leads to periods of growth/new protein synthesis
What is meant by term negative nitrogen balance? What does this lead to?
- Insufficient dietary amino acids to offset degradation of endogenous protein - Leads to wasting disease or starvation
Daily protein requirement?
- 50-100 grams
What is meant by term essential AAs. List them. Special case
- AAs that cannot be synthesized - Pvt Tim Hall = mnemonic - Phe, Val, Thr, Try, Iso, Met, His, Arg, Leu, Lyc - Special case = Arg – can be synthesized, not sufficiently to keep up with needs
Can we synthesize arginine?
- Yes, but not enough to keep up with needs during periods of growth, therefore making it essential AA in infants, but not adults
Is arginine an essential AA? When?
- In infants, not adults.
Which AA promotes would healing especially in pressure ulcer patients?
- Arginine
What foods are complete proteins?
- Meat, fish, eggs, poultry, soy beans