Question

When a bond is created between two nucleotide triphosphates in DNA synthesis, the small molecule released from this reaction is: a. pyrophosphate. b. inorganic phosphate. c. ATP. d. organic phosphate.

Short answer

a. pyrophosphate.

Step-by-step solution

- Understand the context

When DNA is synthesized, nucleotides are added to the growing DNA strand. Each nucleotide added is in the form of a nucleotide triphosphate (NTP).

- Identify the bond formation

During DNA synthesis, a phosphodiester bond is formed between the 3' hydroxyl group of the existing DNA strand and the 5' phosphate group of the new nucleotide triphosphate.

- Determine what is released

When the bond is formed, two of the three phosphates from the nucleotide triphosphate are released as a molecule called pyrophosphate.

- Review the options

Among the given options, the molecule released is: a. pyrophosphate. This aligns with the chemical process described previously.

Key concepts

nucleotide triphosphates

Nucleotide triphosphates (NTPs) are essential building blocks for DNA synthesis. Each NTP consists of three parts: a nitrogenous base, a sugar molecule (deoxyribose in DNA), and three phosphate groups. The nitrogenous base provides the genetic code, which pairs with complementary bases on the existing DNA strand. Nucleotide triphosphates are highly reactive molecules due to their three phosphate groups, making them ideal substrates for forming the DNA chain. This reactivity is crucial for the addition of new nucleotides to the growing DNA strand during replication.

phosphodiester bond

A phosphodiester bond is a chemical bond that forms the backbone of DNA and RNA molecules. This bond links the 3' hydroxyl group of one nucleotide to the 5' phosphate group of the next nucleotide during DNA synthesis. The process of forming a phosphodiester bond involves a condensation reaction, which releases water as a byproduct. As a result, the DNA molecule grows in one direction, from the 5' end to the 3' end. The formation of these bonds is catalyzed by enzymes known as DNA polymerases, which ensure that the new DNA strand is an exact complement to the template strand.

pyrophosphate

Pyrophosphate is a small molecule released when a new nucleotide is added to a growing DNA strand. During DNA synthesis, nucleotide triphosphates are incorporated into the DNA chain, creating a phosphodiester bond. This process releases two of the three phosphate groups from the nucleotide triphosphate as pyrophosphate. The release of pyrophosphate is energetically favorable and helps drive the reaction forward. By being released, pyrophosphate reduces the concentration of reaction products, shifting the equilibrium in favor of further DNA synthesis. Pyrophosphate is then usually hydrolyzed into inorganic phosphates, further pushing the DNA synthesis reaction to completion.