We start with the cell, because so much of what happens to us when we get sick, and how we get healthy again, can be explained by what happens on a cellular level. The cell is extremely complex and I will only touch on the basics in these posts, but at least we can have a rudimentary understanding.Structure of cells
A cell has three basic parts:
1) Plasma membrane: This post will discuss the membrane in more detail.
2) Cytoplasm: All the cellular contents between the plasma membrane and the nucleus and can be further divided into the Cytosol and Organelles.
3) Nucleus: Technically an organelle, but usually considered separately because of its numerous and diverse functions.
Membrane
A membrane lies at the border of the cells. It consists of lipids and proteins.
Phospholipids (one of the three classes of membrane lipids) are formed into what is called a lipid bilayer. This occurs because it is amphiphilic (containing both hydrophobic and hydrophilic properties). The hydrocarbon tails of the molecule are hydrophobic (water repelling) and its polar head is hydrophilic (water loving). As the plasma membrane faces watery solutions on both sides, its phospholipids accomodate this by forming a phospholipid bilayer with the hydrophobic tails facing each other. Picture a row of heads facing the outside of the cell -- which contains water -- with the tails facing in and another layer of the heads facing the inside of the cell with the tails facing in.The membrane acts as a boundary layer to contain the cytoplasm (fluid in a cell). It also acts as a gatekeeper, allowing or denying access to and from the cell. The phospholipids permit lipid-soluble materials to easily enter or leave the cell by diffusion through the cell membrane. The membrane also serves as an anchor to provide the shape of the cell. Cholesterol, another one of the three classes of membrane lipids, helps the membrane to keep its shape.
The molecular arrangement of the membrane resembles an ever-moving sea of lipids that contains a mosaic of many different proteins. The proteins may float freely, be moored at specific places, or be moved through the lipid sea. The peripheral proteins lie on the surface of the membrane and the integral proteins extend into, and sometimes through, the membrane.Proteins serve many functions in the cell membrane. Transport proteins function as the shipping and receiving department of the membrane. They can transport molecules across the cell membrane. Receptor proteins can detect chemical signals to pass between cells and systems. Proteins also participate in the enzyme activity important in such functions as metabolism and immunity.
It is amazing that something so minuscule as a cell membrane can also be so complex and elegantly constructed. We have only touched upon the form and function of the cell membrane, and yet we've seen enough to marvel at its grand design.
How does it affect you?
It could be said that when membranes go wrong, much else can too. Most diseases involve the cell and specifically the membrane, because of its many functions.
Sugar stimulates the pancreas to release insulin. The targets for insulin are muscle, fat and liver cells. These cells have insulin receptor sites on the outside of the cell membrane. A series of events begin when insulin has bound to the receptors, but in Type 1 diabetes, for instance, the process doesn't work.
