A DNA sample is found to contain 15% A residues. Use Chargaff's rules to estimate the percent G residues. 15% G 20% G 30% G 35% G

Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
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**Understanding Chargaff's Rules**

**Question:**
A DNA sample is found to contain 15% A residues. Use Chargaff's rules to estimate the percent G residues.

**Options:**
- 15% G
- 20% G
- 30% G
- 35% G

**Explanation:**
Chargaff's rules state that in any given DNA sample, the amounts of adenine (A) and thymine (T) are equal, and the amounts of guanine (G) and cytosine (C) are equal. This is because A pairs with T and G pairs with C.

If the percentage of adenine (A) is 15%, then the percentage of thymine (T) will also be 15%.

The total percentage of A and T combined is:
\[ 15\% + 15\% = 30\% \]

Since the total proportion of all bases in DNA must equal 100%, the remaining percentage (which consists of both G and C) is:
\[ 100\% - 30\% = 70\% \]

As per Chargaff's rule, the percentage of guanine (G) will be equal to the percentage of cytosine (C), hence:
\[ \frac{70\%}{2} = 35\% \]

**Answer:**
35% G
Transcribed Image Text:**Understanding Chargaff's Rules** **Question:** A DNA sample is found to contain 15% A residues. Use Chargaff's rules to estimate the percent G residues. **Options:** - 15% G - 20% G - 30% G - 35% G **Explanation:** Chargaff's rules state that in any given DNA sample, the amounts of adenine (A) and thymine (T) are equal, and the amounts of guanine (G) and cytosine (C) are equal. This is because A pairs with T and G pairs with C. If the percentage of adenine (A) is 15%, then the percentage of thymine (T) will also be 15%. The total percentage of A and T combined is: \[ 15\% + 15\% = 30\% \] Since the total proportion of all bases in DNA must equal 100%, the remaining percentage (which consists of both G and C) is: \[ 100\% - 30\% = 70\% \] As per Chargaff's rule, the percentage of guanine (G) will be equal to the percentage of cytosine (C), hence: \[ \frac{70\%}{2} = 35\% \] **Answer:** 35% G
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