1 The liver clears 50 65 of dietary amino acids In general what does the liver use free amino acids for In other words what is the fate of those dietary amino acids absorbed by the liver I am not asking about specific individual amino acids but you should be able to describe their use in general 20 of those amino acids are used for protein and N containing compound systems Liver protein synthesis o some proteins remain in liver and some are plasma proteins Liver synthesis of nonprotein N nitrogen compounds 2 Know the physiological function of the few amino acid derived nitrogen containing compounds I discussed in class Namely glutathione carnitine creatine carnosine and choline Liver synthesis of nonprotein N compounds o Glutathione a tripeptide scavenger of free radicals antioxidant o Carnitine made from lysine in foods of animal origin FA transport to mitochondria requires vitamin C o Creatine high energy phosphate bond phosphocreatine for ATP synthesis Manufactured from arginine and glycine in kidney and methionine in liver urinary excretion is an indicator of muscle mass o Carnosine Manufactured from histidine and alanine found in meat antioxidant Maintains osmolarity functions as buffer most abundant in muscle o Choline Manufactured from serine in food as lecithin PC acetylcholine neutrotransmitter phosphatidylcholine phospholipid membrane incorporate choline as a headgroup 3 Know the few amino acid derived hormones I discussed in class The three catecholamines serotonin and histamine Catecholamines dopamine norepinephrine epinephrine derived from tyrosine Serotonin Melatonin derived from tryptophan Thyroid hormone tyrosine Histamine derived from histidine 4 What sources contribute to the body s free amino acid pool Amino acids from cell breakdown Amino acids from diet 5 How does the size of this free amino acid pool compare to the total protein in the body The size of the free amino acid pool is smaller than the total protein in the body You need to synthesize structural proteins plasma proteins peptide hormones biogenic amines enzymes immunoproteins and transport proteins 6 Why does essential amino acid deficiency result in negative nitrogen balance Because protein synthesis cannot skip a missing amino acid The unfinished peptide product will be degraded and free amino acids get oxidized There is poor quality of protein consumed and you are excreting more than you are consuming from feces urine and skin hair 7 In what tissue are the branch chain amino acids metabolized for energy Branched chain amino acids leucine isoleucine valine are metabolized in the muscle 8 Understand transamination What does it start with and what does it produce Transamination starts with an amino acid usually alanine or aspartate and a keto acid typically alpha ketoglutarate Transamination ends with a alpha amino acid usually glutamate and pyruvate or oxaloacetate Two reactions o Alanine alpha ketoglutarate pyruvate glutamate o Aspartate alpha ketoglutarate oxaloacetate glutamate 9 Know that the amino acids that can be metabolized into any TCA cycle intermediates or pyruvate are glucogenic Those become acetyl CoA or acetoacetate are ketogenenic Understand why Amino acids that can be metabolized to ANY TCA cycle intermediate are glucogenic because they can be used to make glucose any can produce oxaloacetate which can be used in gluconeogenesis Amino acids that become acetyl CoA or acetoacetate cannot be used to make glucose and are ketogenic These amino acids can be used for fatty acids synthesis or ketogenesis 10 What reaction produces ammonia Do we want ammonia to build up in the blood Oxidative deamination reaction of glutamate No It can cause sudden death at high levels Two ways to get rid of ammonia o Make urea o Excretion through kidney NH3 H NH4 11 Does the urea cycle require energy What does it produce Where does the nitrogen in urea come from Yes It requires 3 ATP The nitrogen comes from aspartate free ammonia ammonia from It produces urea fumarate can enter TCA cycle deamination reaction of glutamate 12 Name two amino acids that carry nitrogen out from muscle to the liver What happens to their nitrogen in the liver Glutamine Alanine Their nitrogen is used to make urea 13 When glutamine is produced and released by the muscle it can be taken up by the liver the intestinal cells or the kidney a What may the liver use glutamine for The liver takes the nitrogen off of glutamine and uses it along with aspartate to make urea b What do the enterocytes need glutamine for The enterocytes may use glutamine to make enzymes proteins and energy since oxaloacetate glutamate a ketoglutarate aspartate a ketoglutarate can enter the TCA cycle and be used to create energy c When blood pH is low the kidney will use more glutamine Why Free ammonia NH3 in the kidney reacts with a proton to form ammonium NH4 which is excreted in the urine Ammonium is basic so it counteracts the acidic pH Note glutamine glutamate NH3 14 Glutamine is also important for the rapidly dividing growing cells such as the enterocytes and immune cells Why NUCLEOTIDE SYNTHESIS Glutamine is an energy source for these rapidly growing cells Oxaloacetate glutamate aspartate a ketoglutarate a ketoglutarate can enter the TCA cycle and generate energy 15 What hormones promote N retention protein synthesis and what hormones promote protein catabolism Insulin and growth hormone promote N retention for synthesis of new proteins Glucocorticoids glucagon and epinephrine promote protein catabolism need to increase energy 16 What is protein turnover Does it contribute to BMR RMR Protein turnover is the synthesis and degradation of proteins Yes The energy cost of protein turn over is approximately 10 25 17 What determines protein quality Is amino acid composition the only factor Amino acid composition is not the only factor Chemical or amino acid score o Comparison between amino acid standard o If the amino acid score matches the RDA requirement it is a quality protein Protein digestibility o Decrease protein quality for those that are not digestible i e feathers Protein efficiency ratio gain in body weight per gram of protein consumed Nitrogen balance o Low quality proteins need to be supplied at high amount to maintain nitrogen balance 18 Know how much nitrogen do proteins have on average or how much protein 1g N represents Remember the numbers There is 1g nitrogen per 6 25 grams of protein 19 How is the amount of dietary protein required to reach