18. Protein metabolism

Question 1

Is protein content really different across men/women/obese?

Answer 1

No, lean body mass remains the same. Only fat changes.

Question 2

What types of proteins are there?

Answer 2

Enzymes, storage proteins, contractile proteins, protecting proteins, hormones, structural proteins

Question 3

Protein metabolism/turnover in human: humans have/ do not have deposition. Protein synthesis is/is not equal to degradation with … gr each.

Answer 3

humans do not have deposition
Protein synthesis is equal to degradation with 350 gr each

Question 4

If 70 gr of protein intake of a human comes from the diet, how is degradation/oxidation then devided?

Answer 4

70 gr intake: 350-70 = 280 gr synthesis from degradation. 70 gr left = oxidation

Question 5

In pigs, 120 gr of protein synthesis (600) = deposition. 300 gr is intake. 480 gr = degrdation. How is metabolism devided?

Answer 5

300 - 120 = 180 gr intake
120 gr deposition
600 - 300 = 300 gr from degradation
480 - 300 = 180 gr oxidation

Question 6

Deposition always means higher … than ….

Answer 6

Synthesis than degradation (for growth)

Question 7

Why does an adult require so much protein?

Answer 7

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

Question 8

Another reason why an adult requires so much protein?

Answer 8

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)

Question 9

Why is there so much turnover of protein?

Answer 9

Bc they get older and get replaced. Re-utilization reduces dietary requirements

Question 10

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?

Answer 10

5 ATP
4 kJ/gr

Question 11

Name three dimensions of protein turnover

Answer 11

gr/day
fraction (k)
half-life (t1/2)

Question 12

What is the half-life formula?

Answer 12

t1/2 = Ln(2)/k = 0.69/k

Question 13

How many times is t1/2 needed to remove ca 100% of protein?

Answer 13

4-5 times

Question 14

What does rapid replacement of protein require?

Answer 14

high turnover/short half-life

Question 15

Metabolic body weight (W^0,75) is used to compare ..

Answer 15

species, not within species

Question 16

Protein turnover expressed as g/W^0,75 max value is give or take ….
In g/day, human max protein turnover would be …

Answer 16

20
520 g/day

Question 17

Protein turnover requires at least …% of ME

Answer 17

20%

Question 18

What is the physiological benefit of protein synthesis, as it is so costly? Name four examples and elaborate them.

Answer 18

• 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.

Question 19

What is the physiological benefit of protein synthesis, as it is so costly? Name four examples and elaborate them.

Answer 19

• 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.

Question 20

Synthesis and degradation of protein are complex processes, difficult to speed up on short term. How are these processes regulated?

Answer 20

• 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

Question 21

If your diet is very high in protein, then there is no variation in..

Answer 21

What is synthesized + catabolized. Net = 0, as synthesis = degradation

Question 22

What nutrients have a priority during post prandial storage?
Ch, fat or proteins?

Why?

Answer 22

Proteins > Ch + fat
Because they lead to the highest heat production.

Question 23

What does secretin do?

Answer 23

• 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

Question 24

Glycogen vs protein synthesis: difference in cost when enlarging a chain with 1 glucose vs enlarge a chain of protein?
Why this difference?

Answer 24

1. To enlarge a chain with 1 glucose, we need 1 ATP and 1 UTP (2 ATP)
2. 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