Question

List and describe the function of the ten subunits constituting DNA polymerase III. Distinguish between the holoenzyme and the core enzyme.

Short answer

#tag_title# DNA polymerase III subunits and functions #tag_content# DNA polymerase III, found in prokaryotes, is responsible for DNA replication and consists of ten subunits: 1. Alpha: Catalyzes DNA synthesis by adding new nucleotides. 2. Epsilon: Removes incorrect nucleotides (proofreading exonuclease). 3. Theta: Enhances epsilon subunit's ability to recognize mismatched nucleotides. 4. Tau: Enables enzyme dimerization for simultaneous leading and lagging strand synthesis. 5. Gamma: Aids in loading and unloading the enzyme onto the DNA template. 6. Delta: Functions as a clamp loader and facilitates beta subunit loading. 7. Delta prime: Assists in the clamp loading process. 8. Chi: Helps the gamma subunit in loading the enzyme at the replication fork. 9. Psi: Stabilizes interactions between the polymerase and DNA template strand. 10. Beta: Sliding clamp proteins that increase processivity by attaching to the DNA template. The core enzyme, consisting of alpha, epsilon, and theta subunits, is the minimal functional unit. The holoenzyme, the fully functional form, contains all ten subunits, providing increased processivity and efficiency during replication.

Step-by-step solution

Introduction to DNA polymerase III

DNA polymerase III is a complex enzyme responsible for DNA replication in prokaryotes, primarily in the bacteria Escherichia coli (E. coli). It consists of several subunits that work together to synthesize new DNA strands, ensuring the accurate transmission of genetic information from one cell generation to another.

List of DNA polymerase III subunits

DNA polymerase III is composed of ten different subunits. Each subunit plays a specific role in the replication process. The following is a list of these subunits and a brief description of their functions: 1. \(\alpha\) (alpha): This subunit is responsible for the polymerase activity that adds new nucleotides to the growing DNA chain, forming phosphodiester bonds. 2. \(\epsilon\) (epsilon): This subunit is the main proofreading exonuclease and is responsible for removing incorrect nucleotides fitted during replication and replacing them with the correct ones, thus increasing the enzyme's overall fidelity. 3. \(\theta\) (theta): This subunit enhances the ability of the epsilon subunit to recognize and remove mismatched nucleotides. 4. \(\tau\) (tau): Tau is responsible for the dimerization of the enzyme, allowing it to simultaneously synthesize both leading and lagging DNA strands. 5. \(\gamma\) (gamma): This subunit is involved in the loading and unloading process of the enzyme onto the DNA template and possesses ATPase activity. 6. \(\delta\) (delta): Delta helps with the loading of beta subunits onto the DNA strand and functions as a clamp loader. 7. \(\delta'\) (delta prime): Delta prime also aids in the clamp loading process. 8. \(\chi\) (chi): Assists the gamma subunit in loading the enzyme at the DNA replication fork. 9. \(\psi\) (psi): It stabilizes interactions between the polymerase and the DNA template strand. 10. \(\beta\) (beta): These are sliding clamp proteins that attach to the DNA template, forming a ring structure. The clamp proteins enhance the processivity of the enzyme by keeping it firmly attached to the DNA during replication.

Holoenzyme vs. Core enzyme

The core enzyme is the minimal functional unit of DNA polymerase III, consisting of the alpha, epsilon, and theta subunits. It is responsible for catalyzing DNA synthesis and proofreading exonuclease activity. However, the core enzyme alone is not very processive, meaning it can only add a few nucleotides before dissociating from the DNA template. The holoenzyme, on the other hand, is the fully functional form of DNA polymerase III containing all ten subunits. The additional subunits present in the holoenzyme dramatically increase its processivity and overall efficiency, ensuring the rapid and accurate replication of the bacterial genome during cell division.