# Vitamin B9 (Folate)

**Summary**  
Vitamin B9 (Folate) is a water-soluble vitamin that plays a key role as a component of THF (tetrahydrofolate). THF serves a key role in methylation reactions, such as those required for DNA and RNA synthesis. Folate is present in leafy green vegetables, and it is absorbed in the jejunum of the small intestine.

**Key Points**  
- **Folate (Vitamin B9)**  
  - Converted to **tetrahydrofolic acid (THF)**, a coenzyme for 1-carbon transfer/ **methylation** reactions  
    - key role in **nucleotide synthesis**, especially thymine (see [Purine Synthesis](/content/view/4386/index.html) and [Pyrimidine Synthesis](/content/view/4541/index.html))  
  - Found in **leafy green vegetables** (“folate from foliage”)  
  - Absorbed in the **jejunum**

Find Folate Biochemistry and other [Vitamins](/content/browse#playlist-2700/index.html) among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.