Problem 10 - Biology: The Unity and Diversity of Life

Question

Energy that drives the attachment of a nucleotide to the end of a growing strand of DNA comes from ______. a. ATP b. DNA polymerase c. the nucleotide d. a and c

Step-by-Step Solution

Answer

The energy comes from the nucleotide itself.

Step 1: Analyze the DNA Extension Process

During DNA replication, nucleotides are added to a growing DNA strand by the enzyme DNA polymerase. This enzyme facilitates the process, but the energy required to add each nucleotide comes from the nucleotides themselves.

Step 2: Identify the Source of Energy

Each nucleotide added to a DNA strand is in the form of a triphosphate. When a nucleotide triphosphate is added to the DNA strand, two phosphate groups (pyrophosphate) are cleaved off, releasing energy that drives the attachment process.

Step 3: Evaluate the Options

Option a. ATP is a common energy source in cellular processes but not specifically for DNA nucleotide attachment. Option b. DNA polymerase facilitates the process but does not supply energy. Option c. the nucleotide itself, in its triphosphate form, provides the energy for its own attachment. Option d. combines both ATP and nucleotide, but we should select the most specific and direct source of energy which is c.

Key Concepts

Nucleotide Triphosphate

Nucleotide triphosphates play a critical role in the process of DNA replication. At its core, a nucleotide triphosphate consists of a nitrogenous base, a sugar molecule, and three phosphate groups. This structure is specially designed to store energy, necessary for various cellular processes, including DNA replication.
When a nucleotide triphosphate is incorporated into a growing DNA strand, it donates its energy efficiently.
During incorporation, the enzyme DNA polymerase facilitates the addition of the nucleotide. Two of the three phosphates (which form part of the triphosphate group) are cleaved off, releasing pyrophosphate. This release results in the energy needed to form a phosphodiester bond between the incoming nucleotide and the existing DNA strand.
Thus, nucleotide triphosphates not only provide the building blocks for DNA but also the necessary energy for their own incorporation, making them essential components for DNA synthesis.

DNA Polymerase

DNA polymerase is the enzyme responsible for stringing together nucleotides to form a new strand of DNA during replication. It can be thought of as the builder of the DNA strand, working with precision and speed.
DNA polymerase performs multiple tasks:

• It selects the correct nucleotide triphosphate to pair with the template strand.
• It facilitates the formation of a phosphodiester bond between the growing DNA strand and the new nucleotide.
• It proofreads the newly formed DNA strand, ensuring that any errors are corrected to maintain genetic fidelity.

While DNA polymerase is crucial to the replication process, it does not supply the energy required for the incorporation of nucleotides. Instead, it relies on the energy from the nucleotide triphosphates themselves. Hence, DNA polymerase's role is to guide and facilitate construction rather than drive it energetically.

Energy Source in Nucleotide Attachment

The energy for nucleotide attachment during DNA replication is intrinsic to the nucleotide triphosphates themselves. Each nucleotide, structured as a triphosphate, carries its own packet of energy. This energy is harnessed when two of the phosphates are cleaved off.
Here is why this is significant:

• It provides an immediate, efficient source of energy precisely where and when it is needed in the replication process.
• This self-contained energy system eliminates the need for additional energy transport mechanisms, such as ATP dependence.
• It allows for a rapid and streamlined DNA synthesis process, which is key to efficient cell division and replication.

By understanding that nucleotides carry their own energy source, students can appreciate how elegantly cell biology manages to streamline energy consumption and DNA synthesis processes.