18. Protein metabolism Flashcards
Is protein content really different across men/women/obese?
No, lean body mass remains the same. Only fat changes.
What types of proteins are there?
Enzymes, storage proteins, contractile proteins, protecting proteins, hormones, structural proteins
Protein metabolism/turnover in human: humans have/ do not have deposition. Protein synthesis is/is not equal to degradation with … gr each.
humans do not have deposition
Protein synthesis is equal to degradation with 350 gr each
If 70 gr of protein intake of a human comes from the diet, how is degradation/oxidation then devided?
70 gr intake: 350-70 = 280 gr synthesis from degradation. 70 gr left = oxidation
In pigs, 120 gr of protein synthesis (600) = deposition. 300 gr is intake. 480 gr = degrdation. How is metabolism devided?
300 - 120 = 180 gr intake
120 gr deposition
600 - 300 = 300 gr from degradation
480 - 300 = 180 gr oxidation
Deposition always means higher … than ….
Synthesis than degradation (for growth)
Why does an adult require so much protein?
Mucus secreted by the gut is disproportionally rich in threonine and cysteine.
This depletes tissue pools of these two essential amino acids, leaving an unbalanced amino acid mixture that cannot be used for protein synthesis.
Surplus amino acids = metabolic fuel
Another reason why an adult requires so much protein?
Several of the enzymes of amino acid catabolism have high values of Km so their activity increases as substrate conc increases. However, there is irreversible loss of aa’s as concentration rises above that at which amino acid with lowest Km is saturated (aminoacyl tRNA synthetase)
Why is there so much turnover of protein?
Bc they get older and get replaced. Re-utilization reduces dietary requirements
Translation takes more ATP than transcription. How much ATP does it take to make 1 mol of AA (100 gr protein)? And in kj/gr?
5 ATP
4 kJ/gr
Name three dimensions of protein turnover
gr/day
fraction (k)
half-life (t1/2)
What is the half-life formula?
t1/2 = Ln(2)/k = 0.69/k
How many times is t1/2 needed to remove ca 100% of protein?
4-5 times
What does rapid replacement of protein require?
high turnover/short half-life
Metabolic body weight (W^0,75) is used to compare ..
species, not within species
Protein turnover expressed as g/W^0,75 max value is give or take ….
In g/day, human max protein turnover would be …
20
520 g/day
Protein turnover requires at least …% of ME
20%
What is the physiological benefit of protein synthesis, as it is so costly? Name four examples and elaborate them.
- Compensation lost functional properties
- loss of functional properties of proteins
- loss of functional proteins from the body
- Modification of functional properties
- Net protein synthesis
- increase functional proteins (deposition/growth)
- synthesis excretion products (lactation)
- Substrate cycle = also very important for heat production.
What is the physiological benefit of protein synthesis, as it is so costly? Name four examples and elaborate them.
- Compensation lost functional properties
- loss of functional properties of proteins
- loss of functional proteins from the body
- Modification of functional properties
- Net protein synthesis
- increase functional proteins (deposition/growth)
- synthesis excretion products (lactation)
- Substrate cycle = also very important for heat production.
Synthesis and degradation of protein are complex processes, difficult to speed up on short term. How are these processes regulated?
- by inhibition of the complementary process
When feeding, synthesis remains the same but degradation decreases
When stress, degradation remains the same but synthesis decreases
In steady state, both are equal
See p. 175
If your diet is very high in protein, then there is no variation in..
What is synthesized + catabolized. Net = 0, as synthesis = degradation
What nutrients have a priority during post prandial storage?
Ch, fat or proteins?
Why?
Proteins > Ch + fat
Because they lead to the highest heat production.
What does secretin do?
- Meal induces secretin release
- Secretin activates BAT thermogenesis, which is satiation feedback to the brain
- secretin also induces bicarbonate release from pancreas and biliary system into duodenal lumen
Glycogen vs protein synthesis: difference in cost when enlarging a chain with 1 glucose vs enlarge a chain of protein?
Why this difference?
- To enlarge a chain with 1 glucose, we need 1 ATP and 1 UTP (2 ATP)
- To enlarge chain of protein, we need 5 ATP for protein elongation
Difference explained by fundamental difference between both polymerisation processes:
Glycogen = glu-glu-glu-glu-glu
Protein: specific combination of 20 different possible aa
