### Biotechnologyprinciples And Processes Topic

**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.**