CBSE · Class 12 · Biology · Molecular Basis of InheritanceA double-stranded DNA molecule has a total of 10,000 base pairs. Analysis of the DNA reveals that it contains 20% Adenine. Calculate the exact number of Adenine, Thymine, Guanine, and Cytosine nucleotides present in this DNA molecule, showing all steps clearly.
Step-by-Step Solution
Step 1: Calculate the total number of nucleotides
- Given total base pairs (bp) = $10,000$
- Each base pair consists of 2 nucleotides.
- Total number of nucleotides = $10,000 \times 2 = 20,000$
Step 2: Apply Chargaff's Rules
- According to Chargaff's rules for double-stranded DNA:
- Percentage of Adenine (%A) = Percentage of Thymine (%T)
- Percentage of Guanine (%G) = Percentage of Cytosine (%C)
- Given percentage of Adenine (%A) = $20%$
- Therefore, percentage of Thymine (%T) = $20%$
Step 3: Calculate the percentage of Guanine and Cytosine
- Total percentage of all four bases = $100%$
- $%A + %T + %G + %C = 100%$
- $20% + 20% + %G + %C = 100%$
- $40% + %G + %C = 100%$
- $%G + %C = 100% - 40% = 60%$
- Since $%G = %C$, each will be:
- $%G = 60% / 2 = 30%$
- $%C = 30%$
Step 4: Calculate the absolute number of each nucleotide
-
Number of Adenine (A) nucleotides:
- $= 20% \text{ of } 20,000$
- $= \frac{20}{100} \times 20,000 = 4,000$
-
Number of Thymine (T) nucleotides:
- $= 20% \text{ of } 20,000$
- $= \frac{20}{100} \times 20,000 = 4,000$
-
Number of Guanine (G) nucleotides:
- $= 30% \text{ of } 20,000$
- $= \frac{30}{100} \times 20,000 = 6,000$
-
Number of Cytosine (C) nucleotides:
- $= 30% \text{ of } 20,000$
- $= \frac{30}{100} \times 20,000 = 6,000$
Final Answer:
- Adenine = $4,000$
- Thymine = $4,000$
- Guanine = $6,000$
- Cytosine = $6,000$
💡 Study Guide: This question tests core syllabus concepts from Molecular Basis of Inheritance. For formulas, key summaries, and mock exam reference guides, read the full Molecular Basis of Inheritance Revision Notes.