**Core Concept**
The alpha subunit of G-protein plays a crucial role in signal transduction by interacting with downstream effectors. Upon activation by GTP binding, the alpha subunit dissociates from the beta-gamma dimer and regulates various cellular processes.

**Why the Correct Answer is Right**
The activated alpha subunit of G-protein stimulates or inhibits downstream effectors such as adenylyl cyclase, phospholipase C, or ion channels. For example, in the case of Gs alpha subunit, it activates adenylyl cyclase, leading to an increase in cyclic AMP (cAMP) levels. In contrast, the Gi alpha subunit inhibits adenylyl cyclase, resulting in decreased cAMP levels. This regulatory mechanism allows for precise control of various cellular responses.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incomplete and does not provide any information about the action of the alpha subunit of G-protein.

**Option B:** This option is incorrect because the alpha subunit of G-protein does not directly interact with the beta-gamma dimer to regulate downstream effectors. Instead, it dissociates from the beta-gamma dimer upon activation by GTP binding.

**Option C:** This option is incorrect because the beta-gamma dimer of G-protein plays a separate role in signal transduction, interacting with various effectors such as phospholipase C and ion channels, but not directly regulating downstream effectors like the alpha subunit.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the alpha subunit of G-protein is responsible for the specificity of the G-protein coupled receptor (GPCR) signal transduction pathway. The different classes of G alpha subunits (Gs, Gi, Gq, etc.) determine the downstream effectors that are activated or inhibited, leading to distinct cellular responses.

**Correct Answer: C. The alpha subunit of G-protein stimulates or inhibits downstream effectors such as adenylyl cyclase, phospholipase C, or ion channels.**