Protein 2

Question 1

1. Describe in general how nitrogen gets from an amino acid to urea and list the key steps in this process and the most important intermediates.

Answer 1

1. an amine + ATP+ CO2–>carbamoyl phosphate by carbamoyl phosphate synthetase 1 in the mitochondria
2. Carbamoyl phopshate joins Ornithine in mitochondria by OTC to become citrulline
3. citrulline is shuttled into cytosol where it is turned into Aspartate
4. aspartate is turned into arginosuccinate by arginosuccinate synthase, also a place an amine from glutamate can come in
5. arginosuccinate is turned into arginine and fumarate by arginosuccinate lyase
6. arginine is turned into urea and ornithine by arginase
7. ornithine is shuttled back to mitochondria to continue cycle.

Question 2

2. Describe the regulation of the key steps in the pathway of nitrogen handling.
   (4)

Answer 2

control point 1- directionality of aminotransferases (controlled by product and subsrtate concentrations

control point 2- carbamoyl phosphate synthetase 1

• arginine positively activates it
• N acetyl glutamate is a neccesary activator of CPS!!!

iii) The directionality of oxidative deamination by Glu dehydrogenase depends on the relative concentrations of Glu,α-ketogluterate,NH3.

iv) ATP & GTP are allosteric inhibitors of
Glu dehydrogenase, while ADP & GDP are activators.

Question 3

4. Describe thyroid chemistry and, specifically, understand how thyroxin is produced.

Answer 3

Thyroxin (prohormone) is made from Tyrosine, Deiodinase takes T4-T3

Thyroglobulin- iodinated through thyroperoxidase that oxidizes iodide. T4/ and T3 are cleaved off parent molecule into the blood.

TSH- induces Iodide uptake, stimulates release of T4 and T3

Thyroxin binding globulin transports T4 and T3

Question 4

5. Describe heme metabolism and porphyrias.

Answer 4

porphyrias are inherited defects in heme synthesis

1. glycine and succinyl coa for m to delta aminolevulinic acid (ALA) by delta aminolevulinc acid synthase (mitochondria)
2. Delta ALA is turned to porphobilinogen by delta ALA dehydratase (cytoplasm)
3. we go through a few intermediates until we have Coproperphyrinogen 3 which is shuttled back to mitochondria and turns to protopophyrin 9
4. protoporphyrin 9 turns to heme by ferrochetolase that takes Fe2+
   * heme then inhibits the first step

Question 5

how does muscle export its nitrogen?

how does most tissue?

Answer 5

alanine–> glutamate in liver

glutamine

Question 6

how does lead lead to anemia

Answer 6

it interferes with ferrochetalase and ALA dehydratase