Question

6. Describe the urea cycle in terms of the cellular location, the nitrogen donors, and energetics

Answer 1

UREA CYCLE is also known as ORNITHINE cycle. Is a biochemical reaction that produce urea from ammonia ..

Animals need a way to excrete..those animal which cannot easily remove nitrogen convert it into urea or uric acid via urine cycle..

It occurs mainly in liver

This cycle has five main steps :

The MITROCONDRIAL STAGE:

-CARBOAMYL PHOSPHATE is formed from ammonia and bicarbonate ,by CPS

- OTC condenses carbamyl phosphate and orthinine to form CITRULLINE .

- CITTRULINE is then transferred to the cytosol by SLC25A15.

The CYTOSOLIC STAGE :

-AS condenses CITRULLINE and aspartate to form argininosuccinate .

-arginosuccinate is broken into arginine and fumerate by AL

-ARGININE is broken down into urea and ORNITHINE by arginase .

-ornithine translocase transports ORNITHINE into mitrocondria.

THEREFORE-

the first two steps occur in MITROCONDRIA

1.THE first ENZYME CARBOAMYL PHOSPHATE SYNTHESASE takes ammonia and bicarbonate and form CARBAMYL PHOSPHATE with use of ATP .

2.ORNITHINE TRANSCARBAMOYLASE (OTC)CONDENSEs carbamyl phosphate and ORNITHINE which forms CITRULLINE .the CITTRULINE then moves out of MITROCONDRIA into cytosol of cell by SLC25A15.

THE LAST 3 STEPS TAKES PLACE IN CYTOSOL :

3. ARGININOSUCCINATE SYNTHETASE (AS) TAKES CITRULLINE and condenses it with aspartate to form ARGININOSUCCINATE.it occurs by formation of an intermediate, CITRULLINE -AMP.

4.ARGINOSUCCINATE is then broken into arginine and fumarate by argininosuccinate lyase. FUMARATE is then into another cycle called tca cycle .

5.arginine is broken into UREA and ORNITHINE BY ARGINASE. ORNITHINE AGAIN TRANSPORTED TO MITROCONDRIA BY ORNITHINE TRANSLOCASE to form CITRULLINE.