Protein Degradation and Vitamin D Flashcards
What pathway is used for the degradation of single proteins (not whole organelles)?
Protein ubiquitination and degradation by proteasome
What does ubiquitination of a protein signal?
Signals that they are to be targeted by a proteasome for degradation.
How is ubiquitin activated?
Activated by E1 activating enzyme, which uses ATP and binds ubiquitin to the active of E1, it is then transfered to E2 (ubiquitin-conjugating enzyme). Third step is catalyzed by E3 ubiquitin ligase, transfers ubiquitin from E2 to protein that is to be degraded (target protein). Many different E3s for different target proteins.
How many ubiquitin chains does a protein have to have for it to be recognizes by the proteasome and degraded?
4
What does autophagy mean?
To eat oneself
Why does starvation trigger autophagy?
A way for the cell to degrade some membranes and proteins and make small energy molecules out of it.
What initiaties autophagy?
The formation of an isolation membrane, the isolation expands and engulfs part of the cytosol, forming an autophagosome. The autophagosome fuses with endosomes and lysosomes, bringing degradative enzymes into the autophagosome and degrading the content.
Autophagy is constantly going at some level or another, same with ubiquitination.
What determines vitamin D formation in animals? Duration of light exposure or intensity?
Intensity
Why don’t plants make D3?
Because they don’t have cholesterol, they have a sterol,which is similar.
What form of vitamin D is active?
Only the di-hydroxy vitamin D (with two OH gorups). Eg, after it’s been hydroxlated once in the liver and then again in the kidney.
The second hydroxylation of vitamin D is stimulated by what hormone?
Parathyroid hormone, which thus regulates vitamin D activity in the body.
What does vitamin D do in the body?
It is lipophilic, and binds to a nuclear hormone receptor to elicit a cellular response.
What are three effects of vitamin D?
- Increase calcium mobilization from bone
- Increase renal reabsoption of calcium (means that less calcium is excreted from the body)
- Increases calcium absorption from the intestine
In a nutshell, vitamin D increases plasma calcium levels.
Why is parathyroid hormone only secreted when calcium levels are low?
Calcium inhibits parathyroid hormone secretion, and parathyroid hormone increases vitamin D production (second hydroxylation of vitamin D in the kidney
How can too much vitamin D over a long period of time be bad for you?
Can lead to hypercalcemia, too high of levels of calcium in the blood, and calcium deposition in arteries and kidneys.
