seinäkalvoihin

Seinäkalvoihin, commonly known as cell membranes, are vital structures found in all living cells. They act as a barrier, separating the interior of the cell from its external environment. This selective permeability is crucial for maintaining cellular homeostasis, allowing essential nutrients to enter while preventing harmful substances from getting in and waste products from exiting.

The primary component of a cell membrane is a phospholipid bilayer. Phospholipids are molecules with a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. These arrange themselves into two layers, with the tails facing inward and the heads facing outward, creating a stable barrier in the watery environment of the cell. Embedded within this bilayer are various proteins, which play diverse roles. These can include transport proteins that facilitate the movement of specific molecules across the membrane, enzymes that catalyze biochemical reactions, and receptor proteins that bind to signaling molecules from outside the cell.

The structure of the cell membrane is often described by the fluid mosaic model. This model posits that the membrane is not rigid but rather a fluid structure where phospholipids and proteins can move laterally. This fluidity is essential for many membrane functions, such as cell division, cell signaling, and the transport of substances. Cholesterol molecules are also often found within the membrane, helping to regulate its fluidity. In plant cells, fungi, and bacteria, a rigid cell wall is located outside the cell membrane, providing additional structural support and protection.