Carbohydrates in the Cell Membrane

Andria Emerson, Giulietta Spudich
  • Author
    Andria Emerson

    Andria Emerson has taught high school science for over 17 years. She has a M.S from Grand Canyon University in Educational Leadership and Administration, M.S from Grand Canyon University in Adult Education and Distance Learning, and a B.S from the University of Arizona in Molecular and Cellular Biology.

  • Instructor
    Giulietta Spudich

    Giulietta has taught college students, graduate students and researchers in scientific topics from genomics to biochemistry. She has a PhD in Molecular and Cell Biology.

Learn about the different types of carbohydrates in cell membranes. Understand the importance and function of carbohydrates in cells and cell membranes. Updated: 12/30/2021

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What is a Cell Membrane?

The cell membrane surrounds all cells and acts like a protective gate controlling what enters and exits the cell. The cell membrane is also referred to as the plasma membrane or lipid bilayer.

The cell membrane consists of two layers of lipids (fats). Each layer is made of structures called phospholipids. A phospholipid is a lipid attached to a phosphate group. The head (red part in figure) is made of phosphate. This portion of the phospholipid bilayer is hydrophilic and mixes well with water. The tail (black lines in figure) of the phospholipid is made of lipids. The tail is hydrophobic meaning it does not mix well with water.


The cell membrane is made of phospholipids

image of lipid bilayer showing arrangement of phospholipids


If thousands of phospholipids were placed in an aqueous solution, the structure here would result. This is exactly what happens in the human body. In cells, the phosphate heads face the outside of the cell (environment) and cytoplasm (inside of the cell), and the tails form the inside of the cell membrane. The hydrophilic head coupled with the hydrophobic tail cause the cell membrane to be semi-permeable. This means only certain materials are able to enter and exit the cell.


The cell membrane is made of a lipid bilayer

image showing heads of phospholipids facing outward and tails facing inward


The main components of the cell membrane are lipids, proteins, and carbohydrates. Although these may sound like substances found in food, they are also important molecules for cells.

  • Lipids are the main component of the cell membrane. Lipids are often referred to as fats.
  • Proteins serve as pumps or channels moving materials in and out of the semi-permeable cell membrane. Proteins make up a large portion of the cell membrane.
  • Carbohydrates are compounds that form sugars and are made of carbon, hydrogen, and oxygen. Carbohydrates are found on the cell membrane and are involved in helping cells communicate.

Carbohydrates

The building blocks of carbohydrates are monosaccharides. The general formula for a monosaccharide is {eq}CH_{2}O_{n} {/eq}. This shows the proportion of carbon, hydrogen, and oxygen atoms.

Glucose {eq}C_{6}H_{12}O_{6} {/eq} is an example of a monosaccharide and serves as the body's main source of energy.


Glucose molecule

image of a glucose molecule


Fructose is another example of a monosaccharide. This molecule has the same chemical formula as glucose, but the atoms are arranged differently, giving this molecule unique characteristics. Fructose is found in fruits and some vegetables.


Fructose molecule

Image of a fructose molecule


Disaccharides are formed when two monosaccharides are bonded together. Sucrose is an example of a disaccharide that is made of glucose and fructose.


Sucrose molecule

Image of a sucrose molecule showing two disaccharides linked together


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Coming up next: Major Structural Components of the Cell Membrane

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  • 0:01 Cell Membrane
  • 0:36 What Are Carbohydrates?
  • 1:00 Protection for the Cell
  • 2:16 Cell Recognition
  • 2:55 Different Carbohydrates
  • 3:59 Lesson Summary
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Carbohydrates in Cell Membranes

Cell membrane carbohydrates such as glycolipids, glycoproteins, and proteoglycans are found on the outside surface of the cell. The image below shows typical skin cells and the cell membrane surrounding each cell.

Glycolipids are membrane carbohydrates linked to lipids. They account for 5% of the lipids in the cell membrane. There are three types of glycolipids: glycosphingolipids, glycoglycerolipids, and glycophosphatidylinositols. These carbohydrate chains help in cell-to-cell recognition.

Glycoproteins are membrane carbohydrates linked to proteins. These protein chains account for the majority of protein chains found on the cell membrane. These compounds also help with cell-to-cell recognition.

Proteoglycans are long carbohydrate chains linked to a protein that is embedded in the cell membrane. These structures regulate interactions between components in the cell and communication between receptors. They also control the growth and production of cells.


The cell membrane on these cells contains carbohydrates such as glycolipids, glycoproteins, and proteoglycans

Image showing cells surrounded by cell membrane


The Carbohydrate Chain

A carbohydrate chain is another name given to glycolipids, glycoproteins, and proteoglycans. The main purpose of a carbohydrate chains is cell-to-cell recognition. Carbohydrates can be thought of as an ID badge for a cell. They enable cells to be recognized. For example, carbohydrate chains are responsible for labeling red blood cells according to blood type. They are also important in the immune system. Carbohydrate chains allow the immune system to be able to distinguish cells belonging to the organism and cells that are foreign and need to be destroyed.


Different types of carbohydrate chains on the cell membrane

Image of different types of carbohydrate chains on the cell membrane


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Frequently Asked Questions

How could the structure of carbohydrates be described?

The building blocks of carbohydrates are monosaccharides. The general formula for a monosaccharide is CH2On. Carbohydrates link together and form more complex carbohydrates.

What is the role of carbohydrates in the cell membrane?

Carbohydrates on the cell membrane help cells function properly. Carbohydrates do this in two ways: helping cells recognize each other and providing protection for cells.

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