This lesson describes the structure and functions of a cell membrane. We’ll learn how a cell membrane keeps the cell’s contents contained and helps a cell to produce energy.
Structures and Functions
We and all other living organisms, including bacteria, are made up of cells. Have you ever wondered whether cells can take in food and expel waste material and even produce energy? Let’s find out what a cell membrane is and what role it plays in these essential tasks.The cell membrane is an integral part of every cell because without a cell membrane, there would be no cell. The cell membrane is a very thin layer that surrounds the contents of the cell, holding them inside while also letting specific things pass in and out.
If you think of a cell as a pie, then the cell membrane is like the crust of a pie that holds the delicious filling in.Bacteria are unicellular microorganisms, meaning they are made up of one cell. The cell membrane of a bacteria is a very thin layer, about 8 nanometers in thickness, that covers the whole body of the bacteria. If the cell membrane breaks, the contents inside the cell leak out and the cell dies.
The cell membrane separates the inner fluids of the cell, called cytoplasm, from the surrounding environment. The cell membrane is also referred to as the cytoplasmic membrane. The cell membrane is a selective barrier, allowing useful molecules to enter and waste material to exit from the cell.
Bacterial Cell Membrane: Structure
A phospholipid molecule is the building block for all biological membranes. The phospholipid molecule is made up of three parts:
- The first part contains various types of organic compounds containing the phosphate ions. The phosphate ions (or charged molecules) are negatively charged and hydrophilic in nature, which means that they attract water.
- The second part is the fatty acid chain, more commonly referred to as a lipid. There are different types of fatty acids found in the cell membrane.
Lipid chains are water insoluble and hydrophobic, which means that they repel water.
- The third part is the glycerol head that acts as a connector between the phosphate group and the lipid chain.
So, the bacterial cell membrane consists of millions of these phospholipid molecules lying side by side in two layers known as phospholipid bilayer. The hydrophilic phosphate-containing organic compounds (or PCC) of the top layer face outside of a cell and those of the bottom layer face inside of a cell. The hydrophobic lipid chains of both the layers face inward toward each other. Imagine a grilled cheese sandwich, with the bread representing the hydrophilic PCCs and the melty cheese representing the hydrophobic lipid chains.
There are several protein molecules embedded in the phospholipid bilayer. These are called integral membrane proteins. These proteins have external hydrophobic regions that face the lipid chains and hydrophilic regions that are exposed to the outside and inside of the cell.
Bacterial Cell Membrane: Functions
The cytoplasmic membrane does so much more than just separating the inside from the outside of a bacterial cell. Let’s discuss a few of its important functions.First up is energy production.
The bacterial cell membrane more often exists in a charged energized form, separating the positively charged hydrogen ions (or H+) from the negatively charged hydroxyl ions (or OH-). The separation of charges creates a form of energy called proton motive force (or PMF). This energy is used by the bacterial cell to perform various activities such as motility, transport of molecules in and out of the cell, and production of the cell’s energy in the form of ATP (or adenosine triphosphate).Next up is the permeability barrier. The bacterial cell membrane is semipermeable in nature, where ‘semi’ means partial and ‘permeable’ means penetrable. It prevents leakage of cytoplasmic constituents outside and allows transport of only specific nutrients in and out of the cell.Finally, the cytoplasmic membrane acts as an anchor for important proteins.
The cell membrane is the place where several integral proteins are situated. These proteins are involved in performing functions such as production of energy in the form of ATP and acting as a conduit for transport of hydrophilic nutrient molecules that otherwise cannot pass through the cell membrane. The integral membrane proteins also help the cells to interact or communicate with other cells.
To review, all cells – including bacterial cells – have a cell membrane. It is made up of a thin phospholipid bilayer with several different types of integral proteins embedded within.
The cell membrane is a semipermeable selective barrier, which means that it prevents the cytoplasmic constituents inside the cell from leaking out and allows only some potential nutrients to enter the cell. The proton motive force, or PMF, generated by the bacterial cell membrane helps the bacteria to carry out essential functions, such as production of ATP, motility, and transport of nutrients.