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Chapter 24: Problem 78

When samples of double-stranded DNA are analyzed, the quantity of adenine present equals that of thymine. Similarly, the quantity of guanine equals that of cytosine. Explain the significance of these observations.

Short Answer

Expert verified
The significance of the observation that the quantity of adenine (A) equals that of thymine (T), and the quantity of guanine (G) equals that of cytosine (C) in double-stranded DNA lies in the base-pairing rules, known as Chargaff's rules. A-T and G-C base pairs ensure that the two DNA strands are complementary and maintain the integrity of the genetic information stored in the DNA molecule. This property is crucial for accurate replication and transcription during cell division and protein synthesis. Any changes in the proportion of these bases could lead to genetic mutations and potentially harmful consequences for the organism.

Step by step solution

01

Understanding DNA structure

DNA (deoxyribonucleic acid) is a molecule that stores genetic information in living organisms. It consists of two long chains (or strands) of nucleotides, each forming a helical structure and held together by hydrogen bonds between the bases. The DNA strands are complementary, which means that each base on one strand pairs with a specific base on the other strand.
02

Identifying the bases and their pairing rules

There are four nitrogenous bases in DNA: adenine (A), thymine (T), guanine (G), and cytosine (C). They follow specific pairing rules, known as Chargaff's rules. Adenine always pairs with thymine (A-T), and guanine always pairs with cytosine (G-C). This is due to the specific chemical structure of each base, which allows them to form hydrogen bonds only with their complementary base.
03

Relating base pairing to the given observation

The observation that the quantity of adenine equals that of thymine and the quantity of guanine equals that of cytosine can be explained by their base-pairing rules. Since A always pairs with T and G always pairs with C, there must be an equal number of A and T bases, as well as an equal number of G and C bases, to form the double-stranded DNA. Each A-T base pair contributes a single adenine and a single thymine molecule, while each G-C base pair contributes a single guanine and a single cytosine molecule.
04

Significance of the observations

The equal amounts of adenine-thymine and guanine-cytosine base pairs in double-stranded DNA ensure that the two DNA strands are complementary and maintain the integrity of the genetic information stored in the DNA molecule. This property is crucial for the accurate replication and transcription of genetic information during cell division and protein synthesis. Any changes in the proportion of these bases could lead to genetic mutations and potentially harmful consequences for the organism.

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