Final answer:
Cell-surface receptors are integral proteins categorized as G-protein coupled receptors, enzyme-linked receptors, or ion channel-linked receptors. The correct answer are options 1,2.
Step-by-step explanation:
When examining the types of cell-surface receptors, it is essential to differentiate between various kinds, as each serves a distinct role in cellular communication and signal transduction. The main categories of cell-surface receptors include ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.
The first category, known as G-protein coupled receptors (GPCRs), are integral membrane proteins that initiate a signaling cascade upon ligand binding, leading to various cellular responses. Secondly, receptor protein tyrosine kinases (RTKs) are a type of enzyme-linked receptor that phosphorylates specific tyrosine residues on certain proteins, which can initiate a series of intracellular signaling events. Thirdly, ligand gated channels open or close in response to the binding of a ligand, allowing specific ions to pass through the membrane and thus alter the cell's internal conditions.
Regarding the specific examples provided in the question:
- G-protein coupled receptors (GPCRs) are indeed cell-surface receptors.
- Receptor protein tyrosine kinases (RTKs) are also cell-surface receptors.
- Ligand gated channels, as well as the specific receptors on B and T cells, fall under the category of cell-surface receptors as well.
- Conversely, steroid hormone receptors are not categorized as cell-surface receptors because they are located intracellularly and interact with lipid-soluble ligands that can pass through the cell membrane.
Therefore, the correct options that are examples of cell-surface receptors are 1) G-protein coupled receptors (GPCRs), 2) Receptor protein tyrosine kinases (RTKs), and 3) Ligand gated channels as well as specific receptors (B and T cell).