Protein and Amino Acids Quiz 1. Peptide absorption plays a great role in the digestion and utilization of protein fed to an animal. It allows uptake of peptides at a faster rate than free amino acid (AA), and is more efficient. Unlike free amino acids, some peptides can be digested and absorbed intact. Peptides subjected to hydrolysis are transported as free amino acids after cleavage. Peptides that resist this luminal hydrolysis and remain intact, relatively speaking, are transported across the brush border and hydrolyzed by cystolic peptidases. The brush border of the villi as related to protein digestion is of great importance due it being where digestion is completed by enzymes. Protein digestion end products, di-peptides and tri-peptides, are broken into smaller components and absorbed along with amino acids through the mucosal cell of the small intestine. Di- and tri-peptides enter themucosal cell and are broken down into single AA’s and actively transported into bloodstream from the mucosal cell. From the mucosal cell, AA’s move across the basolateral membrane and into the capillaries via diffusion. Once here, they can be transported to different tissues to be absorbed and utilized. Luminal di and tri-peptides are absorbed by a transported and subsequently hydrolyzed by intracellular peptide enzymes. 2. Deficiency and toxicity are on opposite ends of the nutritional requirement spectrum. If an animal is deficient, they are not obtaining the necessary amount of any of the indispensable AA. A folacin deficiency typically has a profound effect on tissue regeneration of epithelial tissues. On the other hand, a toxicity could be characterized as amounts in excess of the animal’s requirement, such as a large amount of an AA into the diet. Methionine toxicity could lead liver and pancreatic lesions. Antagonism is when a nutrient interferes or inhibits the action of another substance. Amino acid antagonism canbe corrected by adding a structurally similar AA. Imbalances result from a lack of proportion between nutrients. Amino acid imbalances can be caused by adding one, or multiple, AA’s as opposed to the limiting AA. If not monitored, improper amino acid composition can affect the nutritional value of protein and thus the animal cannot synthesize certain AA sufficiently. 3.a) Plasma lysine remains constant in the blood plasma if dietary lysine intake is constant. b) Plasma lysine increases sharply and then levels out, as the animal reaches maintenance. Similarly, as lysine intake increases, protein deposition increases in a linear fashion. c) Lysine requirement for growing pigs is between 0.6-1.5% according to the NRC for swine. d) The empirical method has a variety of shortcomings in comparison to the factorial method. The availability of AA, genetics of the animal, and the environment are examples of variables that can skew the response with this method.4. Ideal protein differs greatly for ruminants and non-ruminants due to differences in anatomy and digestion. The synthesis of AA via microbial fermentation in the rumen may reduce the importance of the protein quality for ruminants. Hence, urea can be a suitable N-source for lactating dairy cows. In ideal protein each essential amino acid is equally limiting for performance in feeding and there is minimal amount of nitrogen. This concept also applies to limiting N excretion without inhibiting performance. A diet with ideal protein for use in pigs and poultry is important for minimizing cost and increasing performance and profit. Pigs will need a diet with 10 indispensable AA and adequate amounts of nonspecific N to meet dispensable AA needs. 5. The use of isomers and analogs are of considerable importance because they can be an inexpensive option in the production setting, can lower the N content in the diet, as well as reduce N