Question

The integration of signals from more than one pathway can be performed by intracellular signaling proteins via several different mechanisms. As shown in the figure, the pathways controlled by signals A and B interact at the internal protein X, which must acquire two phosphates in order to transmit the signal to downstream targets. Consider the three possible mechanisms for integration described below.

I Pathway A adds one phosphate; pathway B adds the other phosphate.
II Either pathway A or pathway B can add both phosphates.
III Pathway A adds both phosphates; pathway B removes one phosphate.

Which of these mechanisms would transmit a downstream signal if signals A and B were both present?
1) III
2) I
3) I and II
4) II

Answer 1

The combination of Mechanisms I and II ensures that protein X, a key intracellular signaling protein, acquires both phosphates, allowing effective transmission of downstream signals when signals A and B are both present. This integrated approach provides a comprehensive and adaptable mechanism for cellular responses.So the correct option is 3) I and II.

Step-by-step explanation:

In the context of intracellular signaling proteins, the mechanism that would transmit a downstream signal when both signals A and B are present is a combination of Mechanisms I and II.

Mechanism I: Pathway A adds one phosphate, and Pathway B adds the other. This ensures that protein X acquires both phosphates, allowing it to transmit the signal downstream.

Mechanism II: Either pathway A or pathway B can add both phosphates. In this case, the flexibility lies in the fact that regardless of whether A or B adds the phosphates, the end result is the same – protein X gets both phosphates, transmitting the signal downstream.

This combined approach (I and II) allows for a robust integration of signals from both pathways, providing a versatile system for responding to the presence of both signals A and B. It ensures that downstream targets receive the appropriate signals for a coordinated cellular response.So the correct option is 3) I and II.