Protein Types within the Cell Membrane

ORGANIZATION OF THE CELL

The cell is bound by a cell membrane, contains liquid called “cytoplasm,” and contains organelles, which are different structures that perform various functions in the cell. The boundary of the cell is the plasma membrane or “cell membrane.” The membrane is semipermeable, meaning that it lets some molecules in and keeps other molecules out. Oxygen and nutrients are allowed in the cell, while toxins and waste products are kept out of the cell or extruded from the cell. There are specific pumps that keep a tight control over the concentration of certain solutes, such as potassium and sodium, within the cell itself.

The plasma membrane is mostly a double phospholipid structure. A phospholipid is a molecule that has a polar (hydrophilic or water-loving) and a nonpolar (hydrophobic or water-hating) end. The polar ends are on either side of the membrane, while the middle of the membrane consists of the inner core of the cell membrane. Cholesterol and proteins make up the rest of the plasma membrane.

There are several different types of proteins, including peripheral proteins, which are attached to the inner or outer surface of the membrane, and integral proteins, which are within the membrane itself. These float within the lipid bilayer in what’s called the “fluid mosaic model” of the cell membrane. Water, O2, CO2, and other small lipid soluble molecules (like hydrocarbons) pass through the membrane passively without assistance.

PROTEIN TYPES WITHIN THE CELL MEMBRANE

There are several different types of cell membrane proteins that form different functions. Some of these types of proteins are as follows:

A. Channel proteins—these are integral proteins that provide entryways for certain watersoluble or hydrophilic substances, including polar molecules and charged ions. There is no energy expended in the transfer of these molecules. For this reason, the process is referred to as facilitated diffusion.