## Core Concept
G proteins, or guanine nucleotide-binding proteins, are a family of proteins that play a crucial role in transmitting signals from a variety of external stimuli, including hormones, neurotransmitters, and light, inside the cell. They are involved in various cellular processes, including signal transduction pathways that regulate cell growth, differentiation, and metabolism. G proteins are heterotrimeric, consisting of three subunits: α, β, and γ.

## Why the Correct Answer is Right
The correct answer, , implies that one of the statements provided about G proteins is not true. To assess this, we need to evaluate each option based on known characteristics and functions of G proteins. Generally, G proteins activate various effectors, such as adenylyl cyclase, phospholipase C, and ion channels, through their α subunit, which exchanges GDP for GTP to become active. The βγ subunits can also regulate effectors and play a role in receptor-G protein interaction.

## Why Each Wrong Option is Incorrect
- **Option A:** Without the specific details of option A, we cannot directly assess its accuracy regarding G proteins. However, if option A states a known function or characteristic of G proteins, such as their role in signal transduction or their structure, then it would be correct and not the answer.
- **Option B:** Similarly, without specifics, if option B accurately describes a feature of G proteins, like their activation by GTP and deactivation by GTP hydrolysis, it would not be the incorrect statement.
- **Option C:** This option would be incorrect if it accurately represents a property of G proteins.
- **Option D:** This is the correct answer because it implies that one of the provided statements does not accurately describe G proteins. Without specific details on each option, we infer based on common knowledge about G proteins.

## Clinical Pearl / High-Yield Fact
A key point to remember is that G proteins are critical in the signaling pathways of many drugs. For example, β blockers work by blocking β-adrenergic receptors, which are coupled to Gs proteins (a type of G protein) that stimulate adenylyl cyclase activity. Understanding G protein signaling is essential for comprehending the mechanisms of many therapeutic agents.

## Correct Answer: D.