Shortcuts and Tricks to Solve Numerical Problems in Biotechnology - Principles and Processes

1. DNA Sample with 25% Adenine To find the percentage of thymine, remember the Chargaff’s rule: A + T = G + C. Since A is 25%, the complementary T should also be 25%.

2. Nucleotides Coding for Amino Acids Each amino acid is coded by three nucleotides, known as a codon. If the polypeptide chain has 450 amino acids and the gene has 1500 base pairs, divide 1500 by 450 to find the nucleotides per amino acid: 3 nucleotides.

3. Bacterial Culture Doubling Every 20 Minutes In two hours (120 minutes), there will be 6 doubling cycles (120/20 = 6). So, the number of bacteria after 2 hours will be 500 x 2^6 = 32000.

4. Restriction Enzyme and DNA Fragments The total length of the DNA molecule is the sum of the fragment lengths. Therefore, the total length is 3 kb + 5 kb = 8 kb.

5. Purines to Pyrimidine Ratio in DNA Let the number of cytosines be X. Then, the number of purines will be 2000. And, we know the ratio of purines to pyrimidines is 1.2:1 (purines/pyrimidines). Purines/(Purines + Pyrimidines) = 1.2/2.2. By substituting the values, we get 2000/(2000+X) = 1.2/2.2. Solving this equation, we find X = 500. So, the number of cytosines is 500.

6. Recombinant DNA Molecule Size The total size of the recombinant DNA molecule is the sum of the sizes of the foreign gene and the plasmid vector. Therefore, the total size is 5 kb + 10 kb = 15 kb.

7. DNA Replication Resulting in Nucleotide Increase After each replication, the number of nucleotides doubles. So, after 5 replications, the number of nucleotides will be 2^5 times the initial amount. Therefore, the total nucleotides after the 5th replication are 2000 x 2^5 = 32000.

8. Number of DNA Molecules after PCR Each cycle of PCR doubles the number of DNA molecules; there are 30 cycles. So, the number of DNA molecules after 30 cycles become 100 x 2^30 = 1073741824.

9. Percentage of A + T in DNA Since G + C content is 60%, A + T content would constitute the remaining 40%. Thus, the percentage of A + T in DNA is 40%.

10. Number of Guanine Nucleotides in a Gene If guanine nucleotides are 30% of the total 1800 nucleotides, the number of guanine nucleotides in the gene is 0.3 x 1800 = 540.