Amino Acid Metabolism Flashcards
Explain how the process of oxidative deamination (shown below) produces the ammonium ion and what the ammonium ion is used for afterwards to continue amino acid metabolism.
Oxidative deamination is a chemical reaction where glutamate loses its amino group (NH3 + ), with the amino group accepting additional H+ to form the ammonium ion (NH4 + ).
Once glutamate has lost its amino group, it is now a keto acid (alpha-ketoglutarate).
Why does the urea cycle occur in both the cytosol and the mitochondria of the liver cells?
The first step of the urea cycle occurs in the mitochondria, where the required enzyme is located.
Steps 2, 3 and 4 occur in the cytosol, where the required enzymes are located.
A metabolic reaction always occurs where the enzyme(s) needed for the reaction are located.
What is the starting input (reactant) for the urea cycle and what is the final output (end products)?
Input: ammonium ion.
It’s used to create a compound called carbamoyl phosphate that is used in the first step of the urea cycle.
Aspartate is also needed for step 2 of the urea cycle.
Output: urea - which can be taken to the kidney via the blood to be removed from the body.
Where does the input required for the urea cycle come from?
Oxidative deamination removes the amino group from glutamate converting it to an ammonium ion (NH4 + ).
This ion is used to create a compound called carbamoyl phosphate that is used in the first step of the urea cycle.
What must happen to the ammonium ion before the urea cycle can begin?
Before the ammonium ion can be used in the urea cycle it is used to create a compound called carbamoyl phosphate that is used in the first step of the urea cycle.
What is the final output of the urea cycle used for? Why is it necessary for our cells to perform the urea cycle? Why is it important?
The most important output of the urea cycle is urea.
The urea can then be taken to the kidney via the blood for removal from the body. As urea is a nitrogen rich compound, removing urea from the body allows nitrogen to be removed from the body as too much is toxic.
To maintain a nitrogen balance in the body, protein that is not required must be broken down by amino acid metabolism to create urea and remove nitrogen from the body.
Steps 1 and 2 of the urea cycle are anabolic reactions where two smaller components fuse together to become one larger component. Describe the anabolic reactions of the urea cycle shown below.
Step 1 - ornithine and carbamoyl phosphate fuse together to form citrulline.
Firstly, ornithine loses hydrogen atoms from its amino group and carbamoyl phosphate loses its phosphate.
As a result, both ornithine and carbamoyl phosphate require an extra covalent bond (due to losing atoms).
These compounds satisfy their need for an extra covalent bond by attaching to each other, between the nitrogen of ornithine and the carbonyl group within carbamoyl phosphate.
After the new covalent bond has formed the citrulline compound has been created.
Step 2: citrulline and aspartate fuse together to form argininosuccinate.
Firstly, citrulline loses oxygen from a carbonyl group (top) and arginine loses hydrogen atoms from its amino group.
As a result, both citrulline and aspartate require an extra covalent bond (due to losing atoms). These compounds satisfy their need for an extra covalent bond by attaching to each other, between the carbon atom of citrulline and the nitrogen atom within aspartate.
After the new covalent bond has formed the argininosuccinate compound has been created.
Steps 3 and 4 of the urea cycle are catabolic reactions where one large component splits in two to become two smaller components. Describe the breakdown reactions of the urea cycle shown below:
Step 3: argininosuccinate is broken down into arginine and fumarate.
An extra carbon-carbon bond is formed resulting in a double carbon-carbon bond between the central carbon atoms.
To form arginine the remainder of the structure accepts one hydrogen atom to satisfy the bonding arrangements of the nitrogen atom (at the top of the structure).
Step 4: arginine is broken down into urea and ornithine.
To form urea the top part of the structure accepts an oxygen atom from H2O. To form ornithine the nitrogen at the top of the structure accepts additional hydrogen atoms.
The ornithine produced in the final step of the urea cycle (4th step) is then used to begin the first step of the next urea cycle (where ornithine reacts with carbamoyl phosphate).
