**Question:** 2, 3 DPG binds to __________ site of Hb and __________ release of O2

**Core Concept:** The binding of 2,3-diphosphoglycerate (2,3 DPG) to hemoglobin (Hb) plays a crucial role in oxygen transport and release in the context of the Roussel Uclaf (RU) sites. The Roussel Uclaf (RU) sites are named after the French company that discovered them. These sites are located on the Hb molecule and are responsible for the binding of various ligands, including 2,3 DPG.

**Why the Correct Answer is Right:** In this question, we are asked about the binding of 2,3-diphosphoglycerate (2,3 DPG) to hemoglobin (Hb), which leads to the release of oxygen (O2). The correct answer refers to the Roussel Uclaf (RU) sites on the Hb molecule. The RU sites are specific binding sites on the Hb molecule where different ligands bind, affecting oxygen binding properties. In this case, 2,3 DPG binds to the RU site II, which is responsible for promoting the release of O2 from Hb to tissues.

**Why Each Wrong Option is Incorrect:**

A. This option refers to the Roussel Uclaf (RU) sites, but it incorrectly states that 2,3 DPG binds to RU site I. This is incorrect because RU site I is responsible for decreasing the affinity of Hb for oxygen, not promoting its release.

B. This option refers to the Roussel Uclaf (RU) sites, but it incorrectly states that 2,3 DPG binds to RU site III. RU site III is associated with the binding of 2,3 DPG, but it is incorrect in stating that it causes a decrease in O2 affinity. Instead, RU site III is involved in the binding of 2,3 DPG, which increases the O2 affinity of Hb.

C. This option refers to the Roussel Uclaf (RU) sites, but it incorrectly states that 2,3 DPG binds to RU site IV. RU site IV is involved in the binding of 2,3 DPG, but it is not the correct site for promoting O2 release. RU site IV is associated with the binding of 2,3 DPG, which increases the O2 affinity of Hb.

D. This option refers to the Roussel Uclaf (RU) sites, but it incorrectly states that 2,3 DPG binds to RU site V. RU site V is involved in the binding of 2,3 DPG, but it is not the correct site for promoting O2 release. RU site V is associated with the binding of 2,3 DPG, which increases the O2 affinity of Hb.

**Clinical Correlations:**

2,3 DPG is a key regulator of O2 affinity in RBCs, acting on the Roussel Uclaf (RU) sites. This molecule lowers the O2 affinity of Hb