Do Cell Membrane Have Proteins: 9 Facts You Should Know

In this post, you will find the information about, do cell membranes have proteins and their detailed facts around it.

Do cell membrane have proteins, cell membranes of fungi, bacteria, plant and animal cell contains proteins, but their composition and type may vary from cell to cell.

Do cell membrane have proteins?

Yes, cell membrane contain proteins. Basically, cell membranes posses two types of proteins, integral and peripheral proteins. Integral proteins are membrane spanning peptides because they are present in both hydrophilic and hydrophobic regions. And peripheral proteins are are present on the leaflet of the inner side of the membrane. And they can be bound to lipid membrane.

Integral proteins are transmembrane proteins having amino and carboxylic group. They have a charged region of amino acids which are found outside the lipid membrane. The region lies inside the lipid membrane is non polar. Peripheral proteins face inwards cytosol region and they also bind integral proteins. The transmembrane proteins have alpha helix structure.

Why does the cell membrane have proteins?

Proteins in the cell membrane plays various role like binding of signal molecules(hormone and immune mediators). They also transport different nutrients across the membrane against concentration gradient.

Bacteriorhodopsin is a membrane spanning alpha helix protein and it has single chain of polypeptide that folds seven times to form hydrophobic alpha helix structure. The amino group is present at extracellular region while carboxyl group is present at intracellular region. Change in pH, urea and chelating agents causes the peripheral proteins to detach from inner side of membrane.

Where are proteins found in the cell membrane ?

Proteins are found in the interior of the lipid bilayer and also present on the two surfaces. They are called as protein iceberg in the sea of lipids. These proteins can also change their positions in the lipid membrane.

Membrane proteins are divided into two categories, intrinsic and extrinsic proteins. Intrinsic proteins are also called integral proteins, they occur throughout the lipid membrane. These proteins form different channels for the movement of water molecules, ions and other solute particles. Membrane posses some special proteins that work on gate mechanism, means they allow only specific substances to pass.

Does the cell membrane only contain proteins ?

Apart from proteins, cell membrane also posses carbohydrate groups, cholestrol, phospholipids and other types of special proteins. Small carbohydrates or oligosaccharides are bound to proteins and phospholipids forming glycoproteins and glycolipids respectively.

The bacterial cell membrane consists of sensing proteins that helps the bacteria to sense or measure the amount of substances around the cell. Besides theses proteins, there are various transport proteins which help the bacteria to gather the nutrients even if there is less concentration of  nutrients in the environment. These transport proteins are: uniporters, symporters, antiporters, porins or channel proteins and ATP binding cassette (ABC).

Do fungi cell membranes have proteins ?

Fungal cell membranes are composed of phospholipid as that of mammalian cell membrane, but they differ in the lipid composition. Cell membrane of fungi have ergosterol instead of cholestrol which is mainly present in mammalian cells.

The substance ergosterol is synthesized from squalene and squalene is synthesize from acetyl CoA. There is an enzyme present in the cell membrane of fungi, β-1,3 glucan synthase which is required for the synthesis of   β-1,3 glucan.

Do plant cell membranes have proteins?

Like other cell structures, plant cell also have cell membrane which is made up of phospholipids, carbohydrates and proteins are embedded in the plasma membrane. They also contain two types of proteins, intrinsic and extrinsic proteins.

  • Integral proteins are transmembrane proteins having amino and carboxylic group. They have a charged region of amino acids which are found outside the lipid membrane. The amino group is present at extracellular region while carboxyl group is present at intracellular region.
  • Peripheral proteins face inwards cytosol region and they also bind integral proteins. Change in pH, urea and chelating agents causes the peripheral proteins to detach from inner side of membrane.

Do bacteria cell membranes have proteins ?

The bacterial cell membrane is made of phospholipid and act as a barrier or it allows only selective substances to move inside the cell. Bacterial plasma membrane contains different proteins. However, bacterial cell membrane is majorly composed of proteins and phospholipids. The protein content in the cell membrane is about 60% while phospholipids has 40%. This composition may vary from bacterial species as gram-negative bacteria have more proteins in number because of extra cell membrane outside the cell wall.

Gram-negative bacteria contain large amount of porin proteins at the outer membrane  which serves the bacteria for passing of various substances inside the cell in a selective manner. Bacteriorhodopsin is a membrane spanning alpha helix protein and it has single chain of polypeptide that folds seven times to form hydrophobic alpha helix structure.

do cell membrane have proteins
Gram negative bacteria showing cytoplasmic membrane and outer membrane from Wikipedia

The bacterial cell membrane do not contains sterols like eukaryotes, but they usually have saturated fatty acids in their membrane. Most of the bacteria have haponoids, these structures are quite similar to the sterols and provide stability to the cytoplasmic membrane.

Do animal cell membranes have proteins?

Animal cell membrane and all eukaryotic cell contains proteins in their cell membrane. The membrane is composed of phospholipids, carbohydrates and proteins. Glycolipids and cholestrol are the main components of animal plasma membrane. Glycolipids are found exclusively on the outer side of the membrane and constituting about 2% of the lipids of cell membrane.

Illustration of a Eukaryotic cell membrane from Wikipedia
  • On the other hand, cholestrol constitutes the major component of the plasma membrane.
  • In cell membrane, lipids are considered as fundamental structural component but proteins are essential for carrying out different functions of the cell membrane.
  • However, the composition of lipids and proteins is approximately 50% respectively. This can be vary from different eukaryotic cells. Cell membranes posses two types of proteins, integral and peripheral proteins.
  • Integral proteins are membrane spanning peptides because they are present in both hydrophilic and hydrophobic regions.
  • And peripheral proteins are are present on the leaflet of the inner side of the membrane. And they can be bound to lipid membrane.

Difference between Integral proteins and Peripheral proteins.

Integral ProteinsPeripheral Proteins
Integral proteins are membrane spanning peptides because they are present in both hydrophilic and hydrophobic regions.Peripheral proteins are are present on the leaflet of the inner side of the membrane. And they can be bound to lipid membrane. 
Integral proteins are transmembrane proteins having amino and carboxylic group.They are present on the inner side or outer side of the membrane and are bound to lipid membrane.
They are also called Intrinsic proteins.They are also called extrinsic proteins.
Integral proteins constitutes about 70% of the cell membrane.Extrinsic proteins constitutes about 30% of the membrane proteins.
These proteins are firmly attached and cannot be separated from the membrane easily.These proteins may get easily removed from the membrane as they are present at the periphery of the membrane.
Integral proteins are hydrophobic in nature as the large part of the protein is embedded in the lipid bilayer.They are more hydrophilic because they are mostly found at the end regions of the cell membrane.
These proteins functions as enzymes, transport channels and carrier proteins. These proteins functions as signaling molecules, receptors and antigens.
Examples are rhodopsin, NADH dehydrogenase.Examples are erythrocyte spectrin and cytochrome C.

What is the  difference between fungi cell membrane and animal cell membrane ?

Fungi Cell Membrane Animal Cell Membrane
Fungal cell membranes are composed of phospholipid as that of mammalian cell membrane.Animal cell membrane and all eukaryotic cell are composed of phospholipids, carbohydrates and proteins.
 Cell membrane of fungi have ergosterol instead of cholestrol.Glycolipids and cholestrol are the main components of animal plasma membrane.

Conclusion

To wrap up this post, we conclude that cell membrane of fungi, bacteria, plant and animal cell are consists of proteins. The proteins that are present in the cell membrane are of two types, integral and peripheral proteins. Different additional substances are also present in the membrane like sterols, cholestrol and ergosterols. Their presence in the different cell can vary as fungi cells do not contain cholestrol instead they consists of ergosterols.

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