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The Basic Structure of a Cell Membrane

All cells are surrounded by a cell membrane, and its primary purpose is to keep the contents of the cell together. Cell membranes are like many other organelles of a cell because they exist for a specific job. This job is to monitor and control everything that enters and exits the cell. Cell membranes differ depending on the type of cell: animal or plant. For example, an animal's cell membrane has a flexible lipid bilayer, while a plant cell has a rigid cell wall.

  1. The Facts

    • The cell membrane is made up of lipid molecules, called phospholipids. These molecules all have one polar head (which is hydrophilic, meaning "attract water") and two hydrocarbon tails (which are hydrophobic, meaning "repel water"), according to Cellupedia. There are three main classes of lipid molecules that make up a cell membrane. These classes include phospholipids, glycolipids and cholesterol. The particular amount of these lipids vary across membranes.

    Features

    • Cell membranes are also made up of certain proteins with specific functions (as transporters, surface antigens, enzymes and surface receptors). Like the lipid molecules, proteins also have areas that are hydrophobic and hydrophilic, which assist in anchoring the protein inside the cell membrane, according to Cellupedia.

      Furthermore, they are found both inside and outside of the cell membrane, according to Biology4Kids. The proteins that are able to cross the layer of the membrane are key in the active transport of ions and other small molecules.

    Function

    • The way that phospholipids and proteins are arranged within the cell membrane is very important. This is usually referred to as the fluid mosaic model, according to Biology4Kids. The molecules' hydrophilic heads face the waterlike region around the cell, while the hydrophobic tails touch and grind against each other. This action creates two layers of the cell that is referred to as a bilayer.

    Uses

    • Cell membranes have special adaptations for transferring small polar molecules across their surfaces that would otherwise not be able to enter due to the hydrophobic interior. One category is the transport proteins, according to Cellupedia. An example of a transport protein is the channel protein. This type of protein allows solutes to cross the membrane if they are the correct charge and size.

    Types

    • There are various types of transport proteins. Uniports are transport proteins that move solutes (components of a solution) from one section to another. Cotransports are transport proteins that work together to send two solutes. Furthermore, the two types of cotransport systems are symport, in which solutes travel in the same direction, and antiport, in which solutes travel in opposite directions. The particular direction of the solutes is always from an area of more concentration to an area of less concentration.

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