Nitrogen Metabolism 1 Flashcards
Is there nitrogen storage in the body?
No
Amino acids in excess of biosynthetic needs are degraded
- amino group is removed and is converted to urea
- carbon skeletons of amino acids are metabolized
What is the amino acid pool?
This is a reserved stock of amino acids in the plasma and tissues
In a healthy, well-fed individual the input to the amino acid pool balances the output (nitrogen balance)
How big the amino ac8d pool?
About 100 g
What can be the amino acid pool be used for?
- Body protein (about 300-400 g a day) used in protein turn over. To other body protein (about 300-400 g a day)
- Dietary protein (about 70-100 g a day) used for synthesis of N-containing compounds
- Synthesis of nonessential amino acids (varies) followed by amino acids in excess of biosynthetic needs are degraded for energy, glucose, glycogen, fatty acids, ketone bodies
What is the rate of protein turnover?
The rate of protein turnover varies for different proteins. —> half life
- Short lived proteins, with half lives of minutes-hours include many regulatory and midfolded proteins.
- Long lived proteins, with half lives of days-weeks constitute majority of proteins in the cell
What is body protein turnover?
Simultaneous synthesis and degradation of protein molecules
Protein turnover about 300-40l g a day
What chemical signals are used in protein turnover?
Chemical signals for degradation depends on structural aspects and post-translational modifications
- PEST -specific amino acids in primary sequence leads to rapid degradation in proteosome
- Oxidation- randomly occurs
- ubiquitination -marks proteins fir degradation in proteosome
What is ubiquitin-proteosome degradation?
Ubiquitination of proteins is a post-translational modification that targets proteins for degradation
-Requires energy in the form of ATP
Outline the process of ubiquitin-proteosome degradation
- Ubiquitination of selected proteins
- Ub-chains tag proteins for destruction by proteosome
- Destroy the old or damaged protein
- Amino acid pool
What is the proteosome?
The proteosome is a large complex that degrades polyubiquitin-tagged proteins
What is ubiquit?
It is a protein released intact from proteosome
What is nitrogen balance ?
Defines balance between intake of N in the form of dietary protein and the loss of nitrogen mainly in the form of urea
- A healthy well-fed adult is in nitrogen balance as input = output
- Body protein remains constant as rate of protein synthesis is sufficient to replace protein degraded
What is positive nitrogen balance?
- Nitrogen intake exceeds nitrogen excretion
- Increased protein synthesis to support tissue growth and development
- occurs in growing kids, pregnant women and during recovery from trauma
Diets low in protein…
- Leads to deficiency of essential amino acids
- Results in a net breakdown of tissue protein
- Can lead to Kwashiorkor
Diets high in protein…
-No storage for amino acids, so excess is catabolized to ammonia (urea) and the carbon skeletons are converted to glucose or fat
What is negative nitrogen balance?
Nitrogen loss is greater than intake
- this puts metabolic stress to use tissue protein to increase amino acid pool
- inadequate dietary protein and lack of essential amino acids reduces the amount of amino acids in amino acid pool goes to tissue protein
What is the role of dietary protein?
- 70-100 g/day in the typical American diet
- Primary role: used as building blocks for biosynthesis. Provides essential amino acids
- Secondary role: used as an energy source
- About 20% of daily energy requirements derived from protein in typical American diey
- Catabolism of amino acids creates a loss of about 30-55 g/day —> RDA is 56 g/day for a 70kg man
What are the major energy sources of the diet?
Carbs- 50%
Fat- 30%
Protein -20%
What fats(lipids) are used for energy?
Triacylglycerol
Fatty acids, phospholipids and cholesterol
What carbs are used for energy?
Polysaccharides (starch)
- disaccharides (sucrose, lactose)
- Monosaccharides (glucose, fructose, galactose)
What are the energy contributions of each of the dietary components?
Carbs- 4 kcal/g
Protein - 4kcal/g
Fat- 9kcal/g
Alcohol- 7kcal/g
What are the major catabolic pathways of carbs?
- glycolysis
- Pyruvate dehydrogenase
- Tricarboxylic acid cycle
What are the major catabolic pathways of fats?
Fatty acid B-oxidation
What are the major catabolic pathways of proteins ?
Carbon skeletons of amino acids are common intermediates of major catabolic pathways