The Question is from neet-botany molecular-basis-of-inheritance , and it was created by the author B VENKAT

Question

Which of the following DNA sequences would have the highest melting temperature?

B VENKAT · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: DNA Melting Temperature
 **Related Topics**: Hydrogen bonding in DNA, base pairing, DNA stability
 **Prerequisites**: Understanding of DNA structure (base pairing: A-T, G-C), and the concept of melting temperature (Tm).
## SOLUTION PATHWAY
**Given Information**:
  Four DNA sequences: ATATATATAT, AGCTAGCTAG, GCATGCATGC, GCGCGCGCGC
  We need to determine which sequence has the highest melting temperature (Tm).
**Method & Steps**:
 1. Understand the relationship between base pairing and melting temperature.
  Reasoning: The melting temperature of DNA is the temperature at which half of the DNA strands have separated (denatured).  This is largely determined by the strength of the hydrogen bonds between base pairs. Guanine (G) and Cytosine (C) form three hydrogen bonds, while Adenine (A) and Thymine (T) form only two.  More hydrogen bonds mean a higher Tm.
  Formula/Rule:  No single formula is used to calculate Tm precisely, as it depends on several factors (ionic strength, DNA length, etc.). However, the general principle is that a higher GC content leads to a higher Tm.
 2. Calculate the GC content for each sequence.
  Working:
  * ATATATATAT: 0% GC (0/8 bases)
  * AGCTAGCTAG: 25% GC (2/8 bases)
  * GCATGCATGC: 50% GC (4/8 bases)
  * GCGCGCGCGC: 100% GC (8/8 bases)
  Key Point: The percentage of G-C base pairs is the key factor determining the melting temperature.
 3. Determine the sequence with the highest GC content.
  Result: GCGCGCGCGC has the highest GC content (100%).
  Verification:  Since GC base pairs have stronger hydrogen bonding than AT base pairs, a higher GC content directly translates to a higher melting temperature.
 ## OPTION ANALYSIS
A :x: ATATATATAT has only A-T base pairs, resulting in a low melting temperature.
B :x: AGCTAGCTAG has a lower GC content than option C and D.
C :x: GCATGCATGC has a lower GC content than option D.
D ✓: GCGCGCGCGC has 100% GC content, meaning all base pairs are G-C, leading to the highest melting temperature.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing A-T and G-C base pairing: Remember G-C has three hydrogen bonds, A-T has two.
  2.Ignoring the effect of GC content on Tm: The percentage of G-C base pairs is crucial for determining the melting temperature.
 **Quick Tips**:
  1.Focus on the GC content of the sequence; higher GC content means higher Tm.
  2.Remember the strength of hydrogen bonds: G-C > A-T

B VENKAT · Answer

ATATATATAT

B VENKAT · Answer

AGCTAGCTAG

B VENKAT · Answer

GCATGCATGC

B VENKAT · Answer

The correct Option is "GCGCGCGCGC"

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