11) What are the two major degradation products of phenylalanine/tyrosine?12) There is a carbon rearrangement in the degradation of Tyr. Draw the product of this rearrangement. Show which carbons of this product undergo oxidative cleavage in a subsequent step.13) Show by inspection the pathway for degradation of arginine into another proteinacious amino acid.14) Show how the skeleton of histidine maps onto another common proteinacious amino acid. What happens to the non-skeleton carbon of histidine?15) Which amino acids are broken down to -keto glutarate? Which amino acids are broken down to ?16) Which amino acids are essential? What is meant by an essential amino acid?17) What is meant by a conditionally essential amino acid?18) Why are both cysteine and methionine often combined together when estimating the content of essential amino acids?19) How is a PDCAA (protein digestibility corrected amino acid) score determined?20) What does it mean when a protein source has a PDCAA of zero? Does this mean the protein is useless for nutrition?21) What enzyme is responsible for the fixation of nitrogen? What are the energetic requirements for this reaction?22) How many electrons are required to reduce nitrogen gas to ammonia? How many electrons are required in the biological reduction? If these are not the same, explain why.23) What are the two pathways by which glutamate is synthesized? When would each be operative?