Human Protein Nutrition and Metabolism Flashcards
Why do we need urea (to get rid of ammonia?)???
When protein intake exceeds amino acid catabolism…
Total body protein content in the bod increases
Normal growth, anabolism
When protein intake is equal to amino acid catabolism…
Total protein content remains dynamically constant (dynamic equilibrium)
When amino acid catabolism exceeds protein intake…
Total body protein content decreases
Starvation, …
What is the minimum protein requirement?
It is determined by the lowest rate to which the body can reduce its rate of amino acid catabolism and remain in zero body protein balance, i.e. remain in dynamic equilibrium (but the body cannot reduce protein metabolism entirely - we cannot just stop eating protein)
Average daily minimum protein requirement for the adult human
Safe daily protein requirement
Average: 0.65 g per kg of body weight per day
Safe: 0.80 g per kg of body weight per day
Average conventional protein consumption in Canada
1.5 g/kg/d
Body protein balance equation
Body protein balance = protein consumed - protein lost from body
Instead of measuring protein, which can be difficult, we measure…
nitrogen (nitrogen balance)
N balance = N intake - N loss
Composition of myocyte cells
80% water
20% protein
For each g of body protein gained or lost, the hydrated body cell mass increases or decreases by…
5 g
Essential vs non-essential amino acids
Essential: Available ONLY from the diet
Non-essential: Amino acids that the body can synthesize
How do we determine the value of a dietary protein (quality of protein)?
It is determined by the adequacy of its essential amino acid profile
Examples of high-quality proteins
Egg
Milk protein
Beef
Fish
Soy
True or false: Most plant proteins are limited in some essential amino acids and hence of lower quality
True
Amino acid and fuel energy metabolism are intricately regulated
Some condiitons increase the minimum protein requirement - pathological causes
- Renal replacement therapy (dialysis)
- Intestinal fistulas, inflammatory wounds
- Severe tissue damage and requirements for tissue repair
- States of increased protein catabolism
- Systemic inflammation
- Protein maldigestion/malabsorption
The human body eliminates nitrogen in various forms including ammonia, but mostly in the form of ….
urea (detoxified molecule that makes nitrogen “safe”)
Urea synthesis
Carbomoyl phosphatase synthetase I deficiency
Partially blocked pathway, so the organism grows an survives to be born as a human baby BUT cannot transport nitrogen as effectively, causing nitrogen and ammonium buildup in tissues, brain, etc, causing seizure.
Ornithine transcarbamoylase deficiency
Partially blocked pathway increasing ammonium levels and carbamoyl phosphate. Overflow of carbamoyl phosphate leaks out of mitochondria…?
Initial effect of partial metabolic block
Flow rate of the entire pathway slows
Upstream concentrations increase
Downstream concentrations increase
However, successful metabolic adaptation restores relatively normal flow rate.
How does this happen?
A higher substrate concentration increases the impaired enzymes catalytic rate.
How do higher substrate concentrations influence catalytic rate of rate-limiting enzymes?
Higher substrate concentrations approximately ….
Overflow pathway
When a substrate concentration increases upstream of the block there are often…
How to diagnose partially blocked metabolic pathway?
- Clearance is reduced
- Overflow pathways develop
True or false: A sufficiently high concentration can overcome a partial metabolic barrier
Clearance (definition)
It is the distribution of volume that is being cleared of a substrate.
It is NOT the amount of substrate cleared!
To maintain a normal excretion rate, how does the body have to adapt to reduced clearance?
The body has to increase the concentration of the excreted substrate in each ML…
What happens when increased substrate concentration does not….
DEATH (life is impossible under those circumstances)
Examples of metabolic rate diseases
Renal insufficiency
Diabetes mellitus
Ornithine transcarbamoylase deficiency
Homocystinuria
Methionine metabolism
What disease results from beta-..
homocysteine… which is toxic
