This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Bio-Chemistry), Subject name: Biochemistry
Vitamin that acts like a hormone 
Select and explain. 
A. Vitamin K, B. Vitamin B1, C. Vitamin B12, D. Vitamin D
D: Vitamin D
Answer: D: Vitamin D 
Explanation: (D) Vitamin D # Vitamin D is a fat-soluble vitamin that acts as a steroid hormone.> Several hormones, including adrenal and gonadal steroid hormones, thyroid hormones, retinoid hormones, and vitamin D, bind with protein receptors inside the cell rather than in the cell membrane. Because these hormones are lipid soluble, they readily cross the cell membrane and interact with receptors in the cytoplasm or nucleus.> The activated hormone-receptor complex then binds with a specific regulatory (promoter) sequence of the DNA called the hormone response element, and in this manner either activates or represses transcription of specific genes and formation of messenger RNA (mRNA)