Which of the following equations are true for the percen...

Question

Which of the following equations are true for the percentages of nucleotides in double-stranded DNA?

(A)/(T) = (G)/(C)

Accepted Answer

Hi everyone. Let's take a look at this practice problem together. Suppose a DNA sequence contains 20% adenine. What is the percentage of cytosine? The answer options are a 40% B 20% c 30% and D 60%. So for this problem, we need to recall Char gas rule. And Char Gaff's rule recall is about complementary base pairs. It states that adenine is always bonded to thymine and cytosine is always bonded to guanine. Thus, the percentage of adenine is equal to the percentage of thine. And likewise, the percentage of guanine is the same as the percentage of cytosine. Now, there is a formula for this and it is adenine plus guanine equals thymine plus cytosine. Now, since we know that all four bases, the percentages added together must equal 100% of the DNA sequence, we can also think of this as 50% of the sequence is either adenine or guanine and 50% of the sequence is either thymine or cytosine. So in our problem, we have 20% adenine. That means according to Char Gaff's rule, 20% is also thine. So let's plug that into our formula. So we have 20%. Adenine plus guanine equals 20% thymine plus cytosine. Now, since we know that adenine plus guine is 50% that means the percentage of guanine is 30. Likewise, the percentage of cytosine is also 30. And we can check this, the formula works 20%. Adenine plus 30% guanine equals 50% and 20% thymine plus 30% cytosine equals 50%. In addition, if you added up all of these percentages, it would equal 100%. Therefore, we want to find out the percentage of cytosine, which is 30%. So the correct answer is option C 30%. All right, everyone. I hope you found this helpful and I'll see you soon for the next practice problem.

Which of the following equations are true for the percentages of nucleotides in double-stranded DNA?

(A)/(T) = (G)/(C)

Key Concepts

Chargaff's Rules

Base Pairing

Double-Stranded DNA Structure

Watch next

Which of the following equations are true for the percentages of nucleotides in double-stranded DNA?(A)/(T) = (G)/(C)

Key Concepts

Chargaff's Rules

Base Pairing

Double-Stranded DNA Structure

Watch next

Which of the following equations are true for the percentages of nucleotides in double-stranded DNA?

(A)/(T) = (G)/(C)