10. N + C Metabolism Flashcards
In what form does nitrogen have to be excreted from the body? Why?
Urea, bc nitrogen is toxic
Most of amino acids will be lost via ..
urine (70g) vs faecal loss (10g)
But most will be converted to body protein
Amino-acids are not only used to make body protein, but also …
Name example of amino-acid that has a different function than making protein
- Hormones
- Vitamins
- Neurotransmitters
- Antibiotics
E.g. Co-enzyme A (TCA cycle) = amino-acid. Function is to activate a molecule so they can be recognized.
Or: carnitine (lysine + methionine): function is to bring fatty acid into mitochondria for full oxidation.
Structure of amino acid?
- Amino group
- Backbone of carbons
- R-group: very specific for each amino acid
P.100
Conc amino acid in blood?
Concentration amino acid in blood = 1-4 mmol, ~1% of blood osmotic value (very little)
How many amino acids are essential?
9/20
What are semi-essential amino acids?
cannot be synthesized, do not need to be in diet. They can be made from two essential amino-acids (methionine + phenylalanine)
What are conditional essential amino acids?
only essential in certain conditions. E.g. infection, growth..
What broadly happens upon catabolism of amino acids?
C + N part of amino acids follow separate pathways in catabolism:
- C is channeled in gluconeogenesis or TCA cycle
- N is channeled in urea cycle
In catabolism of amino acids, first the C-backbone is deaminated. What two steps are needed for this?
C- backbone is de-aminated (NH4+ removed) by either
1. Transamination
2. Oxidative de-amination
Oxidative deamination of amino acids: where does this happen?
By glutamate dehydrogenase in mitochondria:
(dehydrogenase = something is reduced and something is oxidated). + NADHm = + 2.5 ATP
p.101
What is transamination? Energy?
Transfer of ammonium group to another molecule. No ATP yield/usage
Where does the urea cycle mostly occur?
mostly occurs in the liver
Oxidative de-amination + transamination: what do they have in common?
-> Aim: want to remove nitrogen from an amino acid so we can condensate urea and excrete
-> They are used together
Transamination happens in …., deamination (with use of glutamate dehydrogenase) is only used in …. and leads to …. ATP
Transaminaton can happen in any part in the body. No investing of energy, no production. Glutamate dehydrogenase is only used in the liver. Leads to 2.5 ATP (mNADH)
Why does deamination only occur in the liver?
Deamination: gets rid of the nitrogen part. Only happens in the liver, because the ammonia release is toxic. In the liver, there are enzymes that can enter the urea cycle immediately.
Transamination > deamination > urea. Urea has two ammonium groups, both/one descending from the current reaction
one NH2
Amino acids are similar to …., just the NH3 group needs to be removed
common intermediates
Most amino acids are glucogenic: what is meant by this?
they can be converted to glucose. - C-backbone of glucogenic amino acids are degraded to intermediates of glycolysis or citric acid cycle.
What type of amino acids are not glucogenic?
Ketogenic: - C-backbone of ketogenic amin acids are degraded to Acetyl-CoA.
- Acetyl-CoA has one fate always: enters the cycle and it is fully catabolized
What is the difference between ureotelic and uricotelic animals?
If water balance/weight is not a problem: urea is common product. Easily soluble. We belong to the ureotelic animals.
However, when water balance = problem (e.g. little water in the egg), then uric acid is a common product: has low solubility and crystallizes easily.
Animals like birds excrete uric acid, not urea. They belong to the uricotelic animals
Urea cycle = anabolic. Where does it take place + what does it start with?
Partially mitochondria, partially cytoplasmic
In the liver, always starts with an ammonium from an amino acid.
Urea synthesis step by step:
Step 1?
- Ammonium (most of it from amino acid catabolism)
Use 2 ATP + CO2 tot trap ammonium into carbamoyl phosphate
Urea synthesis step by step:
Step 2?
- Ornithine: condense with carbamoyl phosphate. Releases the phosphate group. Result: citrulline. They are amino acids, used in the urea cycle (so not used to make protein). No energy
Urea synthesis step by step:
Step 3?
- In the cytosol: aspartate leads to the addition of another ammonium by addition of ATP, releasing AMP (so -2 ATP! NOT INDICATED ON MAP :( ). Citrulline > turns into argininosuccinate
Urea synthesis step by step:
Step 4?
- Cytosolic: Arginosuccinate -> arginine (releasing a fumarate) (no energy)
Urea synthesis step by step:
Step 5?
- Arginine: releases urea with the help of arginase. Turns into ornithine = carrier with which we started the cycle. No energy.
When solely considering the urea cycle (not malate/OAA), what is the input and output of the cycle when converting NH4+ to urea?
Start: NH4+
Input: 4 ATP
Output: urea
One NH2 from amino acid
One NH2 from aspartate
2 ATP/N
Where do the NH2s of urea come from? How much ATP/N?
One NH2 = ammonium from amino acid (contributes to half of urea). Requires 2 ATP because the..
Other H2N = from aspartate, also requires 2 ATP
Urea synthesis requires 2 ATP/N
Loss of energy: urea is correction going from DE to ME
ok
Alanine: how many ATPs? (Has one NH2)
- : look at carbon metabolism. Alanine yields pyruvate. Oxidation = 12.5 ATP
- Transamination (no energy)
- Then oxidative deamination (1 NADHm) of gluatamate, removing N group and producing NADHm. But, also investing 2 ATP.
So, 12.5 + 2.5 = 15 ATP. -2 = 13 ATP.
Glucose MW = `180 g/mol
how many glucose can be formed from
- 100 gr glycogen (mw = 162g/mol)
- 100 gr tri-palmitate (MW 806 g/mol)
- kruistabel
= 111 gr - c16 fatty acid -> glucose ? No
100 gr casein: how much gr glucose
MW = 137 gr/mol
Each aa can be converted into PEP, max 1 PEP/aa
MW glucose = 180 g/mol
100 gr = 0.73 mol
0,73 mol PEP (3C)
0,73/2 = 0,36 mol glucose (C6)
0,36 mol glucose
0,36 * 180 = 66 gr glucose
