Question

Why would different kinds of proteins be found on the membranes of cells in different tissues?

Answer 1

The plasma membrane in cells is made of proteins, lipids and carbohydrates (oligosaccharides). The cell membrane has a lipid layer sandwiched between two protein layers (P-L-P structure). The lipid layer is the non-polar layer and is responsible for the fluidity and flexibility of the cell membrane. The protein layer is polar and it is the layer which interacts with the surrounding environment.

Complete answer:
The structural proteins present in cells of different tissues differ. The proteins present in cell membranes have various roles. Some function as channel and carrier proteins, others function as receptors and antigens.
These receptors and antigens are major proteins that differ from cell to cell. The receptors sense specific compounds, hormones and other cells, which stimulates or influences many metabolic reactions within the cells. In fact, the cellular antigens are the proteins by which one can distinguish between the types of cells. For example, the Blood group antigens. The A type blood group and B type blood group can be distinguished by the protein antigen present on the surface of the RBC. If N-acetyl galactosamine is present on the surface of RBCs, then the blood group type is A. And if Galactose is present on the surface, then it is type B. Both N-acetyl galactosamine and galactose may also be present, signifying AB blood group. Thus, antigen helps in cell recognition.
Also, the type of receptors in each cell varies. For example, the receptors of cocaine and some other stimulants are present in the CNS whereas the receptors for the opiates like morphine are present on the CNS and gut. Thus, receptors confer specificity of action for certain compounds and hormones.
Thus, for these reasons, the cells of different tissues have different types of proteins in their plasma membranes.

Note:
One thing to be noted in mind and understand is how the different proteins come up in different cells when the entire genome (DNA) of each cell in an organism is the same?
This is done and achieved with the help of Transcription factors and this is controlled at the transcription and translation phases of DNA. The Transcription factors regulate which parts of the DNA should be transcripted and which parts to be kept dormant. E.g., The genes of blood groups are present in all cells but blood group antigens are only expressed in RBCs.