Problem 9 - Biology Concepts and Applications

Question

Energy that drives the attachment of a nucleotide to the end of a growing strand of DNA comes from ________. a. the nucleotide b. DNA polymerase c. phosphate-group transfers from ATP

Step-by-Step Solution

Answer

Energy comes from the cleavage of phosphate bonds in the nucleotide.

Step 1: Analyze the Energy Source Options

To solve the problem, we need to identify the source of energy that facilitates the addition of a nucleotide to a DNA strand. Consider the three options given: the nucleotide itself, DNA polymerase, and ATP phosphate-group transfers.

Step 2: Understand Nucleotide Structure

Each nucleotide has its own energy source in the form of phosphate groups. When nucleotides are ready to join a growing DNA strand, they exist as deoxyribonucleoside triphosphates (dNTPs), which include three phosphate groups. These groups provide the energy for the attachment.

Step 3: Recognize the Role of DNA Polymerase

DNA polymerase is the enzyme that facilitates the addition of nucleotides to a growing DNA strand. However, it does not provide the energy needed; its role is largely catalytic in nature, positioning the nucleotides and forming bonds.

Step 4: Identify the Correct Energy Source

Energy for the nucleotide addition process comes from the cleavage of high-energy phosphate bonds within the nucleotide itself (dNTPs). When the third phosphate group is released, energy is provided to form a covalent bond with the DNA strand.

Key Concepts

Nucleotide Structure

DNA is made up of smaller units called nucleotides, each playing a crucial role in the genetic makeup of a cell. Understanding their structure is essential. Nucleotides have three main components:

• A nitrogenous base: There are four types, adenine (A), thymine (T), cytosine (C), and guanine (G), that pair up to form the rungs of the DNA ladder.
• A sugar molecule: In DNA, this is a deoxyribose sugar.
• Phosphate groups: Typically, nucleotides start with three phosphates. However, only one remains once integrated into the DNA strand.

The form in which nucleotides participate in DNA replication is their triphosphate version — deoxyribonucleoside triphosphates (dNTPs), making them capable of supplying the energy required for their own incorporation into DNA.

DNA Polymerase

DNA polymerase is a vital enzyme in the process of DNA replication. Its role goes beyond just joining nucleotides. Here's what it does:

• Catalysis: Catalyzes the formation of phosphodiester bonds between nucleotides, connecting them into a continuous DNA strand.
• Template reading: Travels along the template strand, reading the sequence to correctly pair nucleotides.
• Proofreading: Checks and corrects errors to minimize mutations, ensuring the fidelity of DNA replication.

While DNA polymerase is essential, it does not provide the energy for adding nucleotides. It mainly acts as an efficient and reliable catalyst.

Energy Source in DNA Synthesis

The energy required for nucleotide attachment during DNA synthesis is a key point. This energy is derived directly from the nucleotide's own phosphate groups. Here's how it works:

• Phosphate bonds: Nucleotides arrive as triphosphates (dNTPs), containing three phosphate groups.
• Hydrolysis: As a nucleotide is added to the DNA strand, two terminal phosphates are cleaved, breaking high-energy bonds.
• Energy release: The cleavage liberates energy, fueling the formation of a covalent bond between the nucleotide and the growing DNA strand.

In conclusion, this intrinsic energy mechanism is ingeniously efficient, utilizing the nucleotide's structure to self-supply the needed energy.