**Core Concept**
Coenzymes are organic molecules that play a crucial role in enzymatic reactions by facilitating the catalysis of chemical transformations. They often act as electron carriers, shuttle groups, or prosthetic groups that enhance the efficiency and specificity of enzyme-catalyzed reactions.

**Why the Correct Answer is Right**
Coenzymes typically serve as electron carriers or shuttle groups, enabling enzymes to catalyze reactions that involve the transfer of electrons or groups. For instance, NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) are coenzymes that participate in redox reactions, while coenzyme A (CoA) plays a key role in the transfer of acyl groups. By facilitating these reactions, coenzymes help to conserve energy and increase the efficiency of metabolic pathways.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because coenzymes are not typically involved in allosteric regulation, which is a function of allosteric effectors.
**Option B:** Incorrect because cofactors are inorganic ions or metal ions that are required for enzyme activity, whereas coenzymes are organic molecules.
**Option C:** Incorrect because substrate is the molecule being acted upon by the enzyme, whereas coenzymes are involved in the catalytic process.

**Clinical Pearl / High-Yield Fact**
Coenzymes often serve as "molecular middlemen" in enzymatic reactions, facilitating the transfer of electrons or groups and enabling enzymes to catalyze complex chemical transformations. Understanding the role of coenzymes is essential for appreciating the intricacies of metabolic pathways and the mechanisms underlying various diseases.

**Correct Answer:** C.