How do receptors affect cellular responses to external stimuli?

Receptors play a crucial role in cellular responses to external stimuli by initiating a signaling cascade. When a receptor on a cell's surface binds to a specific external signal, such as a hormone or neurotransmitter, it undergoes a conformational change that activates intracellular signaling pathways. This process can involve various secondary messengers that propagate the signal within the cell, leading to a range of biological responses.

For instance, once activated, a receptor might trigger a series of enzymatic reactions or activate proteins that ultimately result in changes such as gene expression, alterations in cellular metabolism, or modifications in cell function. This signaling cascade is essential for cells to communicate and respond appropriately to their environment, allowing them to adapt to changes in external conditions.

In contrast to the correct answer, amplifying a stimulus refers to a process that might occur within a signaling cascade but does not capture the core function of receptors. Blocking external signals describes a scenario where receptors might prevent signal binding but does not reflect their primary role. Lastly, receptors typically do not directly alter DNA. Any changes to gene expression as a result of receptor activation involve several intermediary steps, underscoring that receptors primarily function in transducing signals rather than directly modifying genetic material.