ANSC 303 – Exam 2 Review Fall 2013 Below are a list of concepts and information discussed in class and corresponding examples of questions that may appear on exam 2 related that information. Carbohydrates Carbohydrate Digestion and Metabolism - Non‐ruminant digestion depends largely on enzymatic digestion. This can begin in the mouth (salivary alpha amylase) and/or small intestine. The stomach is not involved! - All species have pancreatic alpha‐amylase o Produced in the pancreas and has specificity for alpha 1‐4 bonded glucose (other bonds are resistant). Therefore, branch points on amylopectin and all chains of cellulose are unaffected. o Pancreatic alpha amylase breaks large non‐structural carbohydrates into small units (dextrins and disaccharides). These are then further digested by brush border enzymes. - Brush border enzymes are produced in this area and function locally. Their activity is specific for a single disaccharide (lactase digests lactose, etc.). The beta 1‐4 bond of cellulose remains untouched. - Any non‐structural carbohydrates that escape small intestine digestion and all structural carbohydrates are subjected to fermentation in the non‐ruminant large intestine. The extent to which this occurs depends on the species of animal (why horses utilize forage well and pigs do not). - Monosaccharides are selectively absorbed by the enterocyte. Glucose is preferred and absorbed by active transport via SGLT‐1 and Galactose shares the same carrier. Fructose depends on facilitated diffusion. - Monosaccharides enter circulation and are metabolized in the liver (fructose and galactose) - Blood glucose levels of non‐ruminant animals are strictly controlled by insulin and glucagon. These hormones act upon muscle and adipose cells. - If a non‐ruminant is fasted, glucose is generated via gluconeogenesis which creates new glucose from nonhexose precursors. Glucose can be created from glycogenolysis, lipolysis (glycerol), and proteolysis (alpha keto acid). - Both non‐structural and structural carbohydrates undergo fermentation in the rumen resulting in production of VFA. o Bacteria favor certain substrates (i.e. Amylolytic prefer starch and cellulolytic like fiber), have ideal pH ranges in which they like to live, and produce specific VFAs as their end product (acetate, propionate, butyrate)  VFA absorbed via passive diffusion from rumen papillae o 1 glucose produces various VFAs and their associated products (carbon dioxide, methane, heat) o VFAs are used for energy for the ruminant animal and other functions (fat synthesis, gluconeogenesis, etc.) o Rumen pH is influenced by saliva flow and diet (starch vs. cellulose). This influences microbe populations, VFA production, and animal health (bloat) o After a carbohydrate meal ruminant animals have less fluctuation in blood glucose levels (because they absorb VFA instead of glucose) and rely less on insulin  However, their low levels of glucose absorption mean they must complete greater amounts of gluconeogenesis to support the needs of cells that require glucose - They preserve this new glucose by lacking enzymes that convert it to fat Example Question: A pig and cow both consume maltose in their diet. As a result of their very different approaches to carbohydrate digestion, the pig will ultimately absorb __________ while the cow will absorb primarily _________. a) Galactose, Acetate b) Glucose, Acetate c) Galactose, Propionate d) Glucose, Propionate Example Question: Farmer Brown feeds his dairy cow an all‐forage diet but would like to increase her milk production by adding grain. When increased levels of starch appear in her diet, the cow’s rumen experiences changes. As a result of increased dietary starch, the rumen pH _________ and populations of cellulolytic bacteria ________. a) Increases, increase b) Increase, decrease c) Decrease, increase d) Decrease, decrease Protein Protein Structure - Protein has various roles and functions in the body, unlike carbohydrates which were primarily a source of energy. - The quality of dietary protein is much more critical for a non‐ruminant animal than a ruminant o Use of NPN o N recycling - The amino acid structure in an amine group bound to an alpha keto acid. The alpha keto acid contains an R chain that varies with individual amino acids. Amino acids are bound together by peptide bonds to create proteins - Amino acids occur in L and D isomers. L is used most efficiently (exception is the use of D Met by chickens) - Crude protein values are determined by the %N in a sample multiplied by 6.25 (because the average protein is 16% N). This value gives no indication of quality. - Amino acids are classified by structure, net charge, polarity, and essentiality. The R chain determines these classifications. -