Chapter 5, Problem 1FIB

Summary Introduction

Introduction:

Cell membrane is semipermeable in nature and it surrounds the cytoplasm of the cell. Other names for cell membrane or cytoplasmic membrane or plasma membrane. The cell membrane keeps the interior of cell separate from outside environment of the cell.

Cell membrane is selectively permeable to some organic molecules and ions. Cell membranes are involved in cell signaling, cell adhesion, and ion conduction.

Answer to Problem 1FIB

Correct answer:

Membranes consist of a bilayer of phospholipids. The five major categories of protein within the bilayer are transport protein, recognition protein, enzymes, connection protein, and receptor proteins.

Explanation of Solution

The bilayer of the cell membrane is made up of amphipathic phospholipids, which consists of two regions: hydrophobic tail region, which repels water and a hydrophilic head region which attracts water. Hydrophobic region prevents diffusion of polar solvents across the membrane.

Innumerable proteins are found attached to the surface of the lipid bilayer. These proteins are divided into five groups on the basis of their functions.

Transport Protein: These proteins regulate the movement of polar solvents across the membrane. These proteins are involved in the formation of channels or gate to make the membrane semipermeable to some ions and organic molecules.

Recognition Protein: These proteins play a major role in immunity. These proteins are made up of specific glycoprotein and the composition varies from person to person. The recognition protein recognizes the “self” molecule, which is found within the same individual and invades the foreign molecule such as a virus.

Enzymes: Enzymes mostly take part in the synthesis and break down of biomolecules. Enzymes found on the surface of the plasma membrane are involved in the breakdown of carbohydrates and proteins that are taken up by the cell as nutrients.

Connection protein: These proteins keep the cell intact within the cytoskeleton and keep the adjacent cells attached to each other. Connection protein also helps in maintaining the cell shape.

Receptor Protein: These proteins are found on the surface of the plasma membrane and contain receptors for messenger molecules such as neurons.

Conclusion

The cell membrane is composed of the lipid bilayer. The lipid bilayer is majorly composed of proteins and carbohydrates. Enzymes, receptor proteins, recognition proteins, transport proteins, and connection proteins are the protein composition of the lipid bilayer.