Sterol, the basic unit of vitamin D, consists of 4 rings they are

Options

A. Three 6-carbon rings one five carbon ring
B. Three 5-carbon rings one six carbon ring
C. Four 6-carbon rings only
D. Four 5-carbon rings only

Answer

To determine the structure of sterol, the basic unit of vitamin D, we need to analyze the composition of its rings. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Structure of Sterols
Sterols are a class of lipids characterized by a core structure of four fused carbon rings. The arrangement and number of carbon atoms in these rings are crucial to identifying the specific type of sterol.

**Hint:** Remember that sterols have a specific arrangement of rings that can be classified based on the number of carbon atoms in each ring.

### Step 2: Identify the Rings in Vitamin D
Vitamin D, specifically vitamin D3 (cholecalciferol), is derived from 7-dehydrocholesterol, which is a sterol. The structure of 7-dehydrocholesterol consists of four rings.

**Hint:** Focus on the fact that the basic unit of vitamin D is derived from a sterol, which has a defined number of carbon rings.

### Step 3: Count the Carbon Atoms in Each Ring
In the case of 7-dehydrocholesterol:
- There are **three rings** that each contain **six carbon atoms** (these are known as cyclohexane rings).
- There is **one ring** that contains **five carbon atoms** (this is a cyclopentane ring).

**Hint:** Visualize the structure of the rings to better understand how many carbons are present in each.

### Step 4: Summarize the Findings
Based on the analysis, we conclude that the basic unit of vitamin D (sterol) consists of:
- **Three six-carbon rings**
- **One five-carbon ring**

**Hint:** When summarizing, clearly state the number of each type of ring to avoid confusion.

### Final Answer
The correct answer is: **Three six-carbon rings and one five-carbon ring.**