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45 Cards in this Set
- Front
- Back
Protein digestion in monogastrics: Oral cavity |
Mechanical breakdown, no proteolytic digestion |
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Protein digestion in monogastrics: Corpus and Fundus |
HCl from parietal cells hydrolyzes some bonds and activates pepsinogen from chief cells to pepsin |
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Protein digestion in monogastrics: Duodenum |
Enterokinase activates trypsin which in turn, activates other zymogens |
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Protein digestion in monogastrics: Jejunum and Ileum |
Absorption of di and tripeptides and amino acids |
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Phases of Intestinal Peptide Absorption |
Pancreatic Phase Mucosal Phase Delivery Phase |
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What happens in pancreatic phase? |
Protein turned into oligo-peptides through exo and endo peptidases (pepsin) Oligo-peptides are turned into di and tripeptides through enterokinase (trypsin and oligo peptidases) |
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What happens in mucosal phase? |
Pinocytosis of colostrum IgG's (<48hrs) AA carrier transports AAs Some peptides penetrate cell PepT1 transporter transports peptides in by working with Na/H transporter (PepT1 requires H+) |
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What happens in delivery phase? |
IgG's brought to lymph Peptides and AAs transported to portal vein |
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What is the difference between the PepT1 receptor (for protein) and the SGLT1 receptor (for CHOs) |
PepT1 can transport both di and tri peptides
SGLT1 can only pick up mono-saccharides |
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PepT1 found in? Substrates for PepT1? |
Major tissues: Intestine, Kidney, lysosomes
Substrates: Di and Tri peptides, protons |
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What do endopeptidases do? give examples of some endopeptidases |
Hydrolyze bonds in middle of protein to generate small peptides
Ex. Pepsin, rennin, trypsin, chymotrypsin, elastase |
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What do exopeptidases do? give examples of exopeptidases |
Release AA from ends of peptide chains
Ex. Carboxypeptidases A and B |
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Aromatic AAs |
Phe Tyr Trp |
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BCAAs |
Ile Leu Lys Val |
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Glucogenic AAs |
Gly, Ala, Val, Ile, Phe, Trp, Met, Pro, Ser, Thr, Tyr, Asp, Cys, Gln, Asp, Glu, His, Arg |
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Ketogenic AAs |
Lys, Leu |
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Glucogenic and Ketogenic AAs |
Phe Tyr Trp Thr Ile |
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Aromatic AAs are largely metabolized by?? For what?? |
Liver
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BCAAs mostly pass into _______________ but are mainly metabolized in ______________ via ______________ |
Systemic circulation
Muscle
BCAA transaminase |
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Glu is used for? |
Gluconeogenesis in the kidney |
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Glutamate dehydrogenase reaction: 1. Key to doing what? 2. Significance in higher animals (what does this lead to) |
1. Key to fixing/removing NH3-N to/from alpha amino groups
2. Higher animals deficient in alpha-KG so they have: limited ability to carry out this step, need dietary alpha-amino groups, and can't efficiently deal with excess NH3 |
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Tranamination is a critical reaction for |
Metabolic (N) economy |
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Transamination is an equilibrium reaction, meaning that depending on concentration.... (provide example) |
Amino acids can be deaminated or keto-acids can be aminated - In liver/renal failure: dietary supplementation of keto-acids can clean up excess amino groups |
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Examples of common transamination reactions: |
alpha-ketoglutarate --> Glutamate
Pyruvate --> Alanine
Oxaloacetate --> Aspartate |
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Microbial protein flow is ______% of total protein flow in the intestine |
45-60% |
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What makes up Metabolizable Protein? |
Microbial protein + RUP + Endogenous protein |
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What makes up endogenous protein? |
Sloughed cells, intestinal enzymes, etc |
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How is microbial protein made/used? |
1. Absorbed peptides turned into protein 2. Intracellular synthesis from VFAs and NH3 3. Uses AA for own energy |
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Why do we feed urea to cattle? |
Relatively inexpensive N2 source for replacing protein content of diet |
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How much urea can we feed to cattle? |
Upper limit: 1% urea of diet DM or 30% of RDP *Optimal when CP <12% |
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What is the problem with urea and low quality forages? |
Imbalance between the rate of ammonia availability and the availability of carbon for the microbes to produce microbial protein and thus ammonia is absorbed into blood stream (bad) |
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Clinical signs of urea toxicity |
Appear 20-30mins after urea ingestion -Rapid and laboured breathing -Tremors, incoordination, inability to stand and tetany |
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Mechanisms of Urea Toxicity |
1. Increase in rumen ammonia = increase in rumen pH 2. As pH increases, shifts from NH4+ to NH3 3. NH3 absorbed much faster than NH4+ 4. Liver capacity to convert NH3 to urea exceeded 5. NH3 accumulates in blood (TOXIC) |
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How can you treat urea toxicity? |
1. Oral drench with 5% acetic acid (to shift equilibrium back to NH4) 2. Cold water drench (decreases urea hydrolysis) 3. Rapid rumen evacuation (doesn't work great) |
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How do you prevent urea toxicity? |
Proper feed mixing Slow dietary adaptation and ad lib feeding |
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What is the rate limiting enzyme for urea synthesis in liver? |
Arginase |
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What happens to urea? |
Excreted in urine (30%) Most Recycled through saliva or rumen wall through UT (70%) |
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Ruminal protein degradation steps |
1. Microbial proteases & peptidases cleave peptide bonds and release AAs 2. AAs deaminated by microbes, releasing NH3 and Keto-acids |
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Proteins leaving rumen |
Microbial protein Bypass dietary protein Secretions |
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Synthesis of microbial proteins: summary |
Microbes use NH3, keto-acids, and energy to synthesize their own AAs |
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Limitation of microbial protein synthesis |
Synchronized availability of readily fermentable CHOs and NH3 |
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Turnover of microbial proteins |
Microbes lysed by lysozymes in abomasum and releases microbial protein which is digested by proteases |
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Similarities between ruminant and non-ruminant protein metabolism |
Metabolic pathways similar at tissue level Can synthesize non-essential AA Can't synthesize essential AA (need from diet) Tissue proteins constantly undergoing turnover Limited AA storage - need constant supply |
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Differences between ruminant and non-ruminant protein metabolism |
Generally not concerned with AA composition of dietary protein in ruminants Ruminants are highly inefficient at converting dietary protein to milk or meat protein (70-75% of N2 intake excreted in urine and feces) |
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Why are we generally not concerned with AA composition of dietary protein in ruminant diets? |
Type of feed has minimal effect on AA composition of bacteria & protozoa leaving rumen, whereas AA composition of microbes reaching duodenum is similar AND Biological value of microbial protein ~80% |