Question

Which would you expect to have a higher entropy: DNA in its well-known double- helical form, or DNA with the strands separated?

Short answer

Separated strands of DNA have higher entropy.

Step-by-step solution

Understand Entropy

Entropy is a measure of the randomness or disorder of a system. A system with higher randomness has higher entropy.

Identify the States of DNA

Consider the two states of DNA: the double-helical form and the state where the strands are separated.

Analyze the Double-Helical Form

In the double-helical form, the DNA strands are hydrogen-bonded and tightly packed in a regular, orderly structure.

Analyze the Separated Strands

When the DNA strands are separated, they are not hydrogen-bonded and can move independently, resulting in a more disordered state.

Compare Entropy in Both States

The double-helical form is more ordered, while the separated strands are more disordered. Thus, the entropy is higher when the strands are separated.

Conclusion

DNA with separated strands has a higher entropy compared to DNA in its double-helical form.

Key concepts

entropy in biochemistry

Entropy plays a crucial role in biochemistry. It is essentially a measure of randomness or disorder within a system. Higher entropy means more disorder.
In biological systems, higher entropy typically translates to more freedom for molecules to move and interact in various ways. This concept is particularly important when discussing processes like protein folding, enzyme activity, and DNA structure.

Proteins and nucleic acids often assume ordered forms with lower entropy. When these molecules are in their functional, structured forms, they are highly specific and ordered. However, when they are denatured or separated, their molecules exhibit higher randomness and thus have higher entropy. This distinction helps us understand why DNA in its separated strand form has a higher entropy compared to its double-helix form.

DNA structure

DNA, or deoxyribonucleic acid, is the blueprint of life. Its structure is both fascinating and fundamental to understanding genetics.

The DNA molecule is composed of two strands that coil around each other to form a double helix. Each of these strands is a long chain made of smaller units called nucleotides. Every nucleotide consists of a sugar molecule, a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine).

In the double-helix structure, the strands run in opposite directions and are held together by hydrogen bonds between the nitrogenous bases. Adenine pairs with thymine, and cytosine pairs with guanine. This specific pairing is what makes DNA a reliable information storage system.

double-helix versus separated strands

When comparing the double-helix form of DNA to separated strands, several differences emerge, especially in terms of entropy.

In its double-helix form, DNA is well-organized and orderly. The hydrogen bonds between complementary bases hold the structure together firmly. This orderly arrangement results in lower entropy because the system is more predictable and restricted in movement.

On the other hand, when DNA strands are separated, they are free to move independently. There are no hydrogen bonds holding them together in an orderly pattern. This freedom allows for many more possible configurations, contributing to a higher degree of randomness or disorder. Thus, the entropy is higher in the separated strand form.

Understanding this difference helps explain biological processes such as DNA replication and RNA transcription, where DNA strands must be separated to be read or copied.