Answer Happy

Hemoglobin (Hb) and myoglobin (Mb) are the O-carrying proteins in vertebrates. Hb, which is contained within red blood cells, serves as the Ocarrier in bloodand also plays a vital role in the transport of COand H. Vertebrate Hb consists of four polypeptides (subunits) each with a heme group. The four chains are held+together by noncovalent attractions. The affinity of Hb for Ovaries between species and within species depending on such factors as blood pH, stage of development, and body size. For example, small mammals give up Omore readily than large mammals because small mammals have a higher metabolic rate and require more Oper gram of tissue.The binding of O -to Hb is also dependent on the cooperativity of the Hb subunits. That is, binding at one heme facilitates the binding of O at the other hemes within the Hb molecule by altering the conformation of the entire molecule. This conformational change makes subsequent binding of Omore energeticallyfavorable. Conversely, the unloading of Oat one heme facilitates the unloading of Oat the others by a similar mechanism.Figure 1 depicts the O --dissociation curves of Hb (Curves A, B, and C) and myoglobin (Curve D), where saturation, Y, is the fractional occupancy of the O-bindingsites. The fraction of Othat is transferred from Hb as the blood passes through the tissue capillaries is called the utilization coefficient. A normal value is approximately 0.25.Figure 1 -Myoglobin facilitates transport in muscle and serves as a reserve store of O. Mb is a single polypeptide chain containing a heme group, with a molecular weight of18 kd. As can be seen in Figure 1, Mb (Curve D) has a greater affinity for than Hb.The llama is a warm-blooded mammal that lives in regions of unusually high altitudes, and has evolved a type of Hb that adapts it to such an existence. If Curve B represents the O-dissociation curve for horse Hb, which curve would most closely resemble the curve for llama Hb?
A. Curve A
B. Curve B
C. Curve C
D. Curve D