the urea cycle

Question 1

where does the urea cycle occur

Answer 1

both within the mitochondria and cytoplasm of the hepatocyte

because this is where the enzymes required are found

Question 2

what are hepatocytes

Answer 2

the major parenchymal cells in the liver

Question 3

describe the urea cycle process

Answer 3

1. in the mitochondrion, ammonia and co2 are added to ornithine to form citruline
2. another ammonia is added to citruline to make arginine (asparte is also made on the way)
3. arginine is broken down into urea and ornithine and the cycle goes around again
4. through this process, the toxic ammonia is converted into harmless urea, which is easily excreted.

Question 4

what does 1 turn of the urea cycle use up

Answer 4

• 3 ATP equivalents
• 4 high energy nucleotides (PO4-)

Question 5

what is the only compound generated in the urea cycle

Answer 5

urea
everything else is recycled

Question 6

what happens if there are deficiencies of any of the enzymes involved in the urea cycle

Answer 6

higher levels of ammonia in the blood,

so you cant survive without the enzymes

Question 7

what are high levels of ammonia associated with

Answer 7

neurotoxicity

Question 8

why is ammonia neurotoxic

Answer 8

1. Ammonia is able to cross the blood brain barrier VERY easily
2. Once inside it is converted to glutamate under the action of the glutamate dehydrogenase enzyme
3. This means there is a depletion in alpha-ketoglutarate
4. As alpha-ketoglutarate falls so does oxaloacetate ultimately resulting in the
   Kreb’s cycle coming to a halt
5. This results in IRREPARABLE CELL DAMAGE & neural cell DEATH
6. This is the reason why ammonia is neurotoxic