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Exam 3 Review - ANSC303Exam3Review Protein...

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ANSC 303 – Exam 3 Review Below are a list of concepts and information discussed in class and corresponding examples of questions that may appear on exam 3 related that information. Protein Protein Metabolism Once amino acids are absorbed into the blood they are sent to the liver. Once they enter they are o Used for synthesis o Catabolized o Released into circulation Body protein is constantly undergoing turnover – the balance of synthesis vs. degradation o Growth requires synthesis > degradation There is no storage of amino acids in the body: it is converted to structural protein or catabolized Synthesis vs. degradation is regulated by insulin and glucagon o Insulin stimulates synthesis (fed) o Glucagon stimulates degradation (fasted) Catabolism occurs constantly in the liver o Rate indicated by urinary nitrogen excretion as catabolism increases, excretion increases o There is always a minimal nitrogen excretion that occurs even when catabolism is low; this is the endogenous urinary nitrogen o Rates increase with excess dietary protein and protein imbalance Imbalance occurs when needs of first limiting amino acid is not met, all other amino acids are catabolized o Transamination transfers the amino group of one amino acid to another keto acid to create a new amino acid “recycling” of excess amino acids Can produce non essential amino acids Reaction requires vitamin B6 in the form of PLP Must have the specific amino transferase required o Deamination occurs when the carbon skeleton of an amino acid is more valuable (lots of excess or imbalance beyond what transamination can handle) Use of energy Convert it to glucose (gluconeogenesis) Use for fat synthesis Reaction requires vitamin B6 in the form of PLP and the specific dehydratase MUST dispose of the amino group Ammonia converted to urea o The NH 3 that results from deamination is toxic and must be detoxified Variation by species in how this is accomplished (mammals create urea, birds make uric acid) Urea cycle converts ammonia into less toxic urea Occurs in the liver Requires amino acids Requires energy o This is why protein use for energy is inefficient! Example Question: Which essential amino acid is part of the urea cycle?
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a) Arginine b) Lysine c) Methionine d) Valine True or False – An imbalanced diet results in increased rates of transamination and deamination even though the animal is not growing to its full potential. a) True b) False Protein in Animal Diets Defining the quality of protein related to an animal’s requirement for amino acids Protein quality – How closely does the amino acid content of a feedstuff match the animal’s requirement? High quality proteins come closest to meeting an animal’s requirement for essential amino acids (ones that must be offered in the diet because they can not be synthesized in the body). This does not refer to digestibility!
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