Apply and Synthesize Knowledge: Vitamin-D metabolism
Please answer the following questions completely on a separate page.
Describe the relationship between the CYP27B1 gene and 1-α hydroxylase.
Explain the effect of parathyroid hormone (PTH) on a proximal tubule cell of the kidney.
Identify two inactive forms of Vitamin D that are synthesized in the human body and the single active form of Vitamin D.
Compare and contrast the molecular structures of the three forms of Vitamin D you identified above.
How are the names calcidiol and calcitriol related to the structure and function of 25-hydroxyvitamin-D and 1,25-dihydroxyvitamin-D, respectively?
Why are Vitamin D Binding Proteins (VDPs) necessary for the transport of Vitamin D in the blood?
Explain how calcitriol functions to regulate its own production via negative feedback.
How does calcitriol interact with Vitamin D Receptors (VDRs) within enterocytes to increase Ca2+ absorption from the diet?
Why does it make sense that high levels of Ca2+ inhibit expression (i.e. transcription and translation) of the CYP27B1 gene?
Name the three proteins that are produced by an enterocyte in response to Calcitriol binding to the VDR?
How do these proteins work together to increase the movement of Ca2+ from the diet into the blood?
Summative Assignment:
Using the resources provided, try to “tell the story” of how the active form of vitamin D is synthesized, regulated, and utilized by the human body. Start with the UV-catalyzed synthesis of Vitamin D3 in the skin and finish with an explanation of how the active form of vitamin D interacts with Vitamin D receptors to maintain skeletal system health by preventing the development of rickets in children and osteomalacia in adults. 1 page (approximate) length.
Use the rubric and vocabulary lists provided below. Please highlight vocabulary in your work.
RUBRIC
Excellent 5pts
Good 3pts
Needs Improvement 1pt
Vitamin D3 synthesis in the skin is catalyzed by UV radiation.
Vocabulary
7-dehydrocholesterol
Vitamin D3
Catalyze
Keratinocyte
Epidermis
All vocabulary terms are included and used to accurately describe the synthesis of Vitamin D3 in the skin.
Most vocabulary terms are included although some may be used inaccurately.
Few vocabulary terms are used or most are used inaccurately.
Vitamin D3 is transported from the skin to the liver via the circulatory system.
Vocabulary
Vitamin D3
Insoluble/Insolubility
*DBP (Vit-D Binding Protein)
All vocabulary terms are included and used to accurately describe the transport of Vitamin D3 from the skin to the liver.
Most vocabulary terms are included although some may be used inaccurately.
Few vocabulary terms are used or most are used inaccurately.
Vitamin D3 is converted to calcidiol in the liver and then transported to the kidney via the circulatory system.
Vocabulary
Vitamin D3
Calcidiol
25 OH Vitamin D
Enzyme
*DBP (Vit-D Binding Protein)
All vocabulary terms are included and used to accurately describe the conversion of Vitamin D3 to calcidiol in the liver.
Most vocabulary terms are included although some may be used inaccurately.
Few vocabulary terms are used or most are used inaccurately.
Calcidiol is converted to calcitriol in the kidney. The pathway is regulated by parathyroid hormone, calcitriol, and Ca2+ ions.
Vocabulary
Calcidiol
Calcitriol
Enzyme
25 OH Vitamin D
1, 25 OH2 Vitamin D
1-α-hydroxylase
CYP27B1
PTH
All vocabulary terms are included and used to accurately describe the conversion of calcidiol to calcitriol in the liver. Explain how the production of calcitriol is regulated in kidney cells.
Most vocabulary terms are included although some may be used inaccurately.
Few vocabulary terms are used or most are used inaccurately.
Calcitriol, the active form of Vitamin D, is transported in blood and binds to VDRs within target cells causing a response.
Vocabulary
VDRs
Enterocytes
Transport proteins
Membrane Channel
Membrane Pump
Calcibindin
All vocabulary terms are included and used to accurately describe how calcitriol is transported to activate VDRs within intestinal enterocytes. Results of activation are clearly described.
Most vocabulary terms are included although some may be used inaccurately.
Few vocabulary terms are used or most are used inaccurately.
VDR activation increases Ca2+ uptake from the diet that may then be used to mineralize bone and prevent disease in children and adults.
Vocabulary
Enterocyte
Lumen
Calcium ions
Transport proteins
Rickets
Osteomalacia
All vocabulary terms are included and used to accurately describe how VDR activation within enterocytes increases Ca2+ absorption from the diet and provides bone cells with materials for mineralization of bone.
Most vocabulary terms are included although some may be used inaccurately.
Few vocabulary terms are used or most are used inaccurately.
General A&P vocabulary that should be included in your writing where appropriate:
lumen
apical / basal
catalysis
gene expression
diffusion
cytosol
inhibition
microvilli
hydroxyl
enzyme
active transport
brush border
activation
negative feedback
