CBSE 2025, Compartment, Set 1

Question

Given below is the diagram representing the observation made for separating DNA fragments by gel electrophoresis. Observe the illustration and answer the questions that follow:

![Gel Electrophoresis Diagram](https://www.edvaya.com/images/cbse/biology/2025/gel-electrophoresis-wells-diagram.webp)

(a) DNA fragments move in the direction $A \rightarrow B$. Explain.
(b) Name the matrix used and its role in gel electrophoresis.
(c) Mention how the separated fragments can be visualized for further technical use.

Edvaya · Accepted Answer

The correct answer is Subjective. **SOLUTION** * **(a) Movement ($A \rightarrow B$):** DNA fragments are inherently negatively charged molecules (due to phosphate groups). When placed in the wells at end A (cathode/negative electrode) and subjected to an electric field, they get strongly attracted and forcefully move towards the positive electrode or anode at end B. * **(b) Matrix & Role:** The most commonly used matrix is **Agarose gel**. Its role is to provide a microscopic sieving effect; smaller DNA fragments experience less resistance and migrate farther and faster than larger ones, efficiently separating them by size. * **(c) Visualization:** The separated DNA fragments can only be visualized by selectively staining them with a highly specific dye called **Ethidium bromide**, followed by immediate exposure to **Ultraviolet (UV) radiation** (appearing as bright orange bands).

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