Question

A DNA probe of 1000 nucleotides incorporates radioactive nucleotides at 10% efficiency. Number of labelled nucleotides is

• A. 10
• B. 50
• C. 100
• D. 200

Hint:

For labeling problems, use the simple formula: \[ \boxed{ \text{Number of Labelled Nucleotides} = \frac{\text{Percentage Efficiency}}{100} \times \text{Total Nucleotides} } \] For this question, \[ 10\%\ \text{of}\ 1000 = 100 \] This type of direct percentage calculation is commonly asked in biotechnology entrance examinations.

Answer 1

The Correct Option is C

Concept: DNA probes are short, labeled DNA molecules used to detect complementary DNA or RNA sequences. Radioactive labeling is commonly performed using isotopes such as \(^{32}P\). If the labeling efficiency is given as a percentage, it represents the fraction of nucleotides that become radioactive. The number of labeled nucleotides is calculated using \[ \boxed{ \text{Labelled Nucleotides} = \text{Total Nucleotides} \times \frac{\text{Efficiency}}{100} } \]

Step 1: Write the given values.
Total nucleotides \[ =1000 \] Labeling efficiency \[ =10\% \]

Step 2: Calculate the number of labelled nucleotides.
Using the formula, \[ \text{Labelled nucleotides} = 1000\times\frac{10}{100} \] \[ = 1000\times0.10 \] \[ =\boxed{100} \]

Step 3: Select the correct option.
The DNA probe contains \[ \boxed{100\ \text{radioactively labelled nucleotides}} \] Hence, \[ \boxed{Option (C) is correct \]