Advanced Placement (AP) Biology Practice Exam

What are membrane receptors that add phosphates to specific amino acids in proteins called?

1. G-protein coupled receptors

2. Ion channel receptors

3. Receptor tyrosine-kinases

4. Intracellular receptors

The correct answer is: Receptor tyrosine-kinases

Membrane receptors that add phosphates to specific amino acids in proteins are known as receptor tyrosine kinases. These receptors function by autophosphorylation; once a signaling molecule binds to them, they undergo a conformational change that leads to the addition of phosphate groups to specific tyrosine residues on their own tyrosine kinase domains. This phosphorylation serves as a signal for downstream signaling cascades, impacting various cellular processes such as growth, differentiation, and metabolism. Receptor tyrosine kinases are particularly crucial in processes where cell signaling is necessary for regulating cell functions, especially in growth factor signaling pathways. The specificity of these receptors for tyrosine allows for precise regulation of the cellular activities that are initiated in response to external signals. In contrast, G-protein coupled receptors activate G-proteins that relay signals inside the cell, while ion channel receptors allow ions to pass through the membrane upon activation. Intracellular receptors, on the other hand, typically bind to small, hydrophobic signaling molecules and act on gene expression, not directly phosphorylating proteins as receptor tyrosine kinases do. Thus, receptor tyrosine kinases distinctly represent the class of receptors that directly add phosphates to specific amino acids, particularly ty