1. Transport: Membrane proteins play a crucial role in regulating the movement of substances across the cell membrane. This is essential for maintaining the cell's internal environment and carrying out various cellular processes. Some membrane proteins act as channels, allowing specific molecules to pass through passively. Others act as pumps, using energy to actively transport molecules against their concentration gradients.

2. Signal Transduction: Membrane proteins serve as receptors for various signals that originate from the cell's environment. These signals can be hormones, neurotransmitters, or other chemical messengers. When a signal binds to a specific receptor, the protein undergoes a conformational change, triggering a cascade of events within the cell, ultimately leading to a specific response.