The specificity factor (W) estimates the preference of rubisco for CO2 versus O2

where Vc and Vo  are the maximum velocities for carboxylation and oxygenation, respectively, and Kc and Ko are the Michaelis–Menten constants for CO2 and O2, respectively

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#Unit 4. Cell Communication and Cell Signaling

Chromosomal locations of immunoglobulin genes

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#Unit 4. Cell Communication and Cell Signaling

IgM antibodies are produced first in a humoral immune response and tend to be of low affinity.

IgM molecules form pentamers that are stabilized by a single J-chain molecule.

This higher avidity of the pentamer compensates for the low affinity

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#Unit 4. Cell Communication and Cell Signaling

IgG efficiently opsonizes pathogens for engulfment by phagocytes and activates the complement system. The affinity of the individual antigen binding sites for their antigen is therefore critical for the effectiveness of these antibodies, and most of the B cells expressing these classes have been selected in the germinal centers for their increased affinity for antigen after somatic hyper mutation.

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IgA is the principal class in secretions, the most important being those from the epithelia lining the intestinal and respiratory tracts.

Dimeric IgA operates mainly on epithelial surfaces.

This monomeric IgA is predominantly of the subclass IgA1; the ratio of IgA1 to IgA2 in the blood is 10:1.

IgA antibodies produced by plasma cells in the gut are dimeric and predominantly of subclass IgA2; the ratio of IgA2 to IgA1 in the gut is 3:2.

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#Unit 4. Cell Communication and Cell Signaling

IgE 

Present only at very low levels in blood or extracellular fluid but is bound avidly by receptors on mast cells.Antigen binding to this cell-associated IgE triggers mast cells to release powerful chemical mediators that induce reactions such as coughing, sneezing, and vomiting.

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#Unit 4. Cell Communication and Cell Signaling

IgD

B cell antigen receptor and may participate in B cell maturation.Exact function is still unclear, IgD may be involved in humoral immune responses by regulating B cell selection and homeostasis.