What biological macromolecules are found in or around cell membranes?

Answer 1

1. Phospholipids

Phospholipids are major components of the cell membrane. They are similar to fats, but have only two fatty acids rather than three. The third hydroxyl group of glycerol is joined to a phosphate group, which is negative in electrical charge. Additional small molecules, usually charged or polar, can be linked to the phosphate group to form a variety of phospholipids. Phospholipids are described as being amphipathic, having both a hydrophobic and a hydrophilic region. Their tails, which consist of hydrocarbons, are hydrophobic and are excluded from water. Their heads, however, which consist of the phosphate group and its attachments, are hydrophilic, and have an affinity for water.

Because of their structure, when phospholipids are added to water, they self-assemble into aggregates so that the phosphate heads make contact with the water and the hydrophobic hydrocarbon tails are restricted to water-free areas. In the animation below you will see the formation of two such structures: micelle and the phospholipid bilayer.

2. Proteins

Proteins are the most structurally sophisticated molecules known, and account for more than 50% of the dry weight of most cells. Although they are diverse, humans have tens of thousands of different proteins, each with a specific structure and function. they are all polymers constructed from the same set of 20 amino acids. Membrane proteins are classified into two major categories;

a)Integral proteins

b) Peripheral proteins

Integral proteins are generally transmembrane proteins, with hydrophobic regions that completely span the hydrophobic interior of the membrane. The hydrophilic ends of the molecule are exposed to the aqueous solutions on either side of the membrane. Proteins are much larger than lipids and move more slowly, but some do drift. Some membrane proteins seem to move in a highly directed manner, however, many others seem to be held virtually immobile by their attachment to the cytoskeleton.Peripheral proteins are not embedded in the lipid bilayer at all; they are loosely bound to the surface of the membrane, often to the exposed parts of integral proteins.

3. Carbohydrates

Membrane carbohydrates are usually branched oligosaccharides with fewer than 15 sugar units. Some of these oligosaccharides are covalently bonded to lipids, forming molecules called glycolipids. Most are covalently bonded to proteins, which are thereby glycoproteins. The oligosaccharides on the external side of the plasma membrane vary from species to species, among individuals of the same species, and even from one cell type to another in a single individual. The diversity of the molecules and their location on the cell's surface enable oligosaccharides to function as markers that distinguish one cell from another

Answer 2

Biological macromolecules found in or around cell membranes include phospholipids, proteins, and cholesterol. Phospholipids make up the main structure of the membrane, proteins serve various functions such as transport and signaling, and cholesterol helps maintain membrane fluidity.