Biological Systems MCAT Practice Exam 2025 – The Comprehensive All-in-One Guide for Exam Success!

Fetal hemoglobin (HbF) possesses a higher affinity for oxygen compared to adult hemoglobin (HbA). This increased affinity is crucial for the developing fetus, as it allows HbF to effectively extract oxygen from maternal blood across the placenta, despite the lower partial pressures of oxygen present in the fetal environment.

The structure of fetal hemoglobin differs from that of adult hemoglobin, primarily in the composition of its subunits. HbF consists of two alpha and two gamma chains, whereas HbA consists of two alpha and two beta chains. The presence of gamma chains in HbF reduces its interaction with 2,3-bisphosphoglycerate (2,3-BPG), a molecule that decreases hemoglobin's affinity for oxygen. Consequently, the lower levels of 2,3-BPG binding to HbF lead to a greater retention of oxygen.

This characteristic is vital for fetal development as it enhances oxygen uptake from maternal blood, ensuring that the fetus receives adequate oxygen for growth and development. Thus, the increased affinity for oxygen is an essential feature of fetal hemoglobin that supports the unique physiological needs of the fetus during gestation.