Chemistry 451

Lecture #31: Amino Acid Metabolism and the Urea Cycle

Read: pg. 615-625; 640-641; 645; with focus on pages identified in objectives below. Optional Reading: pg 656-658

Optional Listening: We're Here Because Urea

HW: pg. 661 (Study Exercise 3, 4, 5); pg 662 (2,3,6)

Optional HW MAKE-UP (IF you missed at least 10 pts): On separate sheets of paper i) correct exam questions ii) for each question, note page numbers in textbook where correct answers were found.

Objectives:

  1. Know that free amino acids (from degradation of cellular proteins and dietary proteins) are taken up by cells and degraded. The amino group is excreted as urea; the remaining carbon skeleton (alpha-keto acid) can be metabolized to CO2 and H2O or used to make glucose (glucogenic) or ketone bodies (ketogenic) (Fig 20-5, pg 616; pg 624-625; fig. 20-11).
  2. Nitrogen is either moved around between amino acids or eliminated as urea. Recognize examples of transamination (pg 616-617; see examples on pg 641; catalyzed by aminotransferase). In transamination the amine group is just passed around between molecules; there is no net deamination.
  3. Know that glutamate dehydrogenase oxidatively deaminates glutamate to form alpha-ketoglutarate and ammonia (pg. 619). This is net deamination (i.e., free ammonia is released). This ammonia is captured and eliminated as urea. Lack of urea cycle enzymes leads to urea cycle disorders.
  4. Be familiar with substrates, compartmentalization and reactions of the urea cycle (pg. 621; rate limiting enzyme is carbamoyl phosphate synthase I ; pg. 622).
  5. Explain the role of N-Acetylglutamate in regulation of the urea cycle (pg. 623)
  6. Be aware that some amino acids must be obtained from the diet because mammals are not able to synthesize them (Table 20-3; essential vs. nonessential amino acids).
  7. Be familiar with patterns of amino acid synthesis: