# What will be the composition of the second strand of DNA if the first contains 18% guanine, 30% adenine and 20% thymine? 1. Knowing that the chains of the DNA molecule are complementary to each other, we determine the content of nucleotides (in%) in the second chain:
since in the first chain G = 18%, so in the second chain C = 18%;
since in the first chain A = 30%, so in the second chain T = 30%;
since in the first chain T = 20%, so in the second chain A = 20%;

2. Determine the content of cytosine in the first chain (in%).
we summarize the content of three other types of nucleotides in the first DNA strand: 18% + 30% + 20% = 68% (G + A + T);
determine the proportion of cytosine in the first DNA strand: 100% – 68% = 32% (C);
if in the first chain C = 32%, then in the second chain G = 32%.

Answer: C = 18%; T = 30%; A = 20%; G = 32% Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.