AIIMS CRE, SNO-2024: When running small DNA fragments, the agarose concentration should be:

AIIMS CRE, SNO-2024

Pathology & Genetics

Medium

Appeared in: AIIMS CRE, SNO-2024

Explanation

Agarose gel electrophoresis separates DNA fragments by size, with the gel acting as a molecular sieve.
A higher concentration of agarose creates a denser gel matrix, which results in smaller pore sizes.
These smaller pores provide greater resistance to the movement of small DNA fragments, slowing them down and allowing for better separation and clearer resolution between bands of similar size.

Option A: A lower concentration creates a gel with larger pores, which is not effective for separating small DNA fragments. They would migrate too quickly and would not be resolved properly.
Option C: The term 'neutral' is not used to describe the concentration of an agarose gel. Concentration is expressed as a percentage (weight/volume). 'Neutral' typically refers to pH.
Option D: This is a false statement. High-concentration agarose gels are a standard and widely used method for separating small DNA fragments in many molecular biology applications.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Agarose Gel Electrophoresis for DNA Separation as background academic context rather than a clinical decision trigger.
Agarose gel electrophoresis is a fundamental technique in molecular diagnostics for analyzing Polymerase Chain Reaction (PCR) products. This is crucial for identifying infectious agents (like HIV, HPV, or SARS-CoV-2) or detecting genetic mutations associated with diseases.
In forensic science, this method is a key part of DNA fingerprinting (genetic profiling) to analyze DNA samples from crime scenes and compare them to suspects.
What if? If a lab technician used a low-concentration gel to analyze small PCR products from a prenatal genetic screening test, the bands for different alleles might not separate. This could lead to an inability to detect a mutation, resulting in a false-negative result and an incorrect diagnosis for the fetus.

How to Approach the Question

First, identify the core scientific principle being tested: the relationship between the size of molecules being separated (small DNA fragments) and the properties of the separation medium (agarose gel).
Recall or deduce the function of the agarose gel: it acts as a sieve or a mesh to separate molecules by size.
Apply a real-world analogy: to separate small particles like sand from pebbles, you need a sieve with very small holes. To separate large rocks from pebbles, you need a sieve with larger holes.
Translate this analogy back to the question: 'Small DNA fragments' are like the 'sand'. To separate them effectively, you need a 'sieve with small holes'.
Connect the 'hole size' to the 'agarose concentration'. A higher concentration of agarose creates a denser matrix, which means the pores (holes) are smaller.
Conclude that a higher concentration is needed for small fragments. Review the options and select the one that matches this conclusion.

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart B (pp 240-463 of 478) p. 69-71