Answer to Question 1
Ammonia is normally converted to urea in the liver by means of several biochemical steps and eventually excreted as urea. A disruption in any one of the eight component pathways involved in the urea cycle results in disorders of the urea cycle. These pathways are governed by enzymes that undergo a cascade of enzymatic transformations to convert the toxic ammonia molecule to non-toxic, water-soluble urea, which contains two nitrogen groups and is eliminated in the urine. Therefore, urea cycle disorders result in an impaired capacity of the body to excrete nitrogen in the form of urea.
Answer to Question 2
1) A number of courses of action are available to you.
2) You are the best judge of what will work.
3) We will work together to review the options and select a course of action.
Relationship of the spindle-assembly checkpoint (SAC) with the cell-cycle machinery
The phosphorus cycle. Numbers are 1012 g P or fluxes as 1012 g P per year (data from Schlesinger 199
The carbon-nitrogen-oxygen cycle of The Sun
The rock cycle and the Earth’s physical environment
Photos simulating vision with two common visual disorders
The normal cell cycle and each of its growth phases