19: Protein turnover and adaptation

Question 1

What happens when protein intake > excretion?

Answer 1

Positive N balance
Increase in body protein content
Normal state in growth, pregnancy and recovery from loss

Question 2

What happens when protein intake = excretion?

Answer 2

N balance/equilibrium
Normal state in an adult
No change in body protein content

Question 3

What happens when intake < excretion?

Answer 3

Negative N balance
Decrease in body protein content
NEVER NORMAL: indicates illness, trauma or inadequate intake

Question 4

What processes have most protein deposition? In descending order?

Answer 4

Lactation, pregnancy, puberty, baby

Question 5

0.6 gr protein/kg body weight: average requirement
0.75 g /kg body weight = recommendation
> people eat about 1.2 gr/kg
In sports, they recommend 1.2-1.4 g/kg. Normal eating will result in this requirement

Answer 5

ok

Question 6

Regulatory aspects of protien synthesis: differences between 1 and 2 are normally under hormonal control
Can also be regulated with 3 or 4

Answer 6

1 Synthesis
2 Degradation
3 Artificial compounds
4 genetic selection

Question 7

Energy related to protein (kJ/gr):

A synthesis
B urine correction
C ME of dietary protein
D ME of body protein
E Gross energy

Answer 7

A: 4
B: 5.2
C: 17
D: 18.4
E: 23.6

Question 8

Dietary requirements for protein synthesis is required to support three main processes. These are..

Answer 8

1. Renewal of body proteins (A -> A)
   Maintenance of functional properties
2. Interconversion of body proteins (A -> B)
   Adaptation of functional properties
3. Increase of body proteins (A -> A+)
   Net production of functional properties

Question 9

What is needed for these 3 processes in terms of % of synthesis?

Answer 9

1. Maintentance (A->A) ca 20% of synthesis. Unavoidable losses. (this is the 70 gr of 350 gr)
2. Adaptation (A->B) 20 < synthesis < 100%
   Unavoidable losses + extra losses/needs (new aa’s needed)
3. Net deposition (A->A+) = 100% or more
   unavoidable losses + extra losses/needs

Question 10

During onset of net protein deposition, a sudden increase in protein requirements can give rise to problems. If you keep same intake, you need to 1
If you increase intake, 2

Answer 10

1. decrease your turnover rate drastically.
   2 synthesis becomes limiting

Question 11

Try to draw what happens when you have
(A) 60 gr deposition
(B) 100 gr intake
(C) 500 gr protein turnover

Remember, intake = 20% of synthesis

Answer 11

So, 100gr = intake. 400 gr/day = needed from breakdown. Total = 500 gr.

You want 60 gr deposition. 100-60 = 40 left from intake. =20%
40 * 5 = 200 =synthesis = degradation.
160 = synthesis from degradation
200-160 = 40 gr left for oxidation

See p.181

Food becomes limiting for the synthesis that can be performed

Question 12

Try to draw what happens when you have
(A) 60 gr deposition
(B) 150 gr intake
(C) 500 gr protein turnover

Remember, intake = 20% of synthesis

Answer 12

150gr - 60 = 90 gr intake. = 20%
90 * 5 = 450 gr total intake = degradation.
450 - 90 = 360 gr degradation for synthesis.
450 - 360 = 90 gr oxidized.

However, 450 gr + 60 = 510 gr/day = exceeding max capacity of 500/day. Therefore, synthesis = limiting.

Question 13

Turnover: Pays a key role in maintenance, deposition, adaptability
Level is associated with …. requirements
When turnover is to low, 1
When turnover is too high, 2

Answer 13

dietary requirements
1. Protein functions get impaired
2. Liver has certain capacity to excrete urea: toxin

Question 14

 What is the metabolic basis for the protein requirement (=aa) of the body?

Answer 14

Protein turnover to replace infunctional proteins/adapt

Question 15

 Why is the dietary requirement for protein synthesis related to maintenance supposed to be lower than for synthesis related to adaptation?

Answer 15

Because we need aa’s that may not be present in the new protein we want to convert to with adaptation

Question 16

 What can you consider as substrate cycling in protein metabolism?

Answer 16

From protein -> aa -> protein. In between, ATP is invested which results in heat.

Question 17

 What are (dis)advantages of substrate cycling in protein metabolism?

Answer 17

To maintain functional proteins, but has a high energetic cost

Question 18

 What are the energetic costs of protein synthesis?

Answer 18

Synthesis: 5 ATP/mol aa (transcription & translation) or: 4 kJ/gr

Question 19

 Are energetic costs of protein synthesis part of the GE (23.6 kJ/g)?

Answer 19

No

Question 20

What is normally the drive for aa oxidation after a meal? (A) need for energy (B) removal of excessive amino acids (C) protein turnover (D) basal activity of enzymes

Answer 20

Protein turnover

Question 21

 Is loss of biological activity of a protein related to the rate of half-life?

Answer 21

No, not always. Protein may lose its activity but is still present in the body (inactive).