Question

How many molecules of retinol can be generated from one molecule of (\(\beta\)) beta carotene?

• A. One
• B. Two
• C. Four
• D. Eight

Hint:

Beta-Carotene Cleavage: Symmetric central cleavage at $15,15'$ double bond yields EXACTLY 2 molecules of Retinol (Vitamin A).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Enzymatic symmetric central oxidative cleavage of provitamin A carotenoids by $eta$-carotene-15,15'-dioxygenase yields two retinaldehyde molecules which are reduced to retinol.
Key Formula or Approach:
\[ \beta\text{-Carotene (C40)} + \text{O}_2 \xrightarrow{\beta\text{-Carotene-15,15'-Dioxygenase}} 2\text{ Retinal (C20)} \xrightarrow{\text{Retinal Reductase}} 2\text{ Retinol (Vitamin A, C20)} \]

Step 2: Detailed Explanation:
In provitamin A metabolism:
- Beta-Carotene ($\beta$-Carotene) is a symmetrical 40-carbon polyene hydrocarbon containing two $\beta$-ionone rings connected by an 18-carbon conjugated central chain.
- In the intestinal mucosal brush border, the enzyme $\beta$-Carotene-15,15'-Dioxygenase (BCO1) catalyzes central oxidative cleavage at the central 15,15' double bond, splitting one $\text{C}_{40}$ molecule into two molecules of all-trans-retinal ($\text{C}_{20}$).
- Each retinal is subsequently reduced by cytosolic retinal reductase to Retinol (Vitamin A).

Step 3: Final Answer:
Thus, Two molecules of retinol are generated from one molecule of beta-carotene, corresponding to option (B).