Question

Briefly describe the structure of the lipid bi-layer of cells including ligands and receptors. You can use diagrams to support your answer.

this is a past paper question but there are no solutions so i don't know how much to write for this or what to include/not include. Please help and provide a solution that i can check my answer with. thank you

Answer 1

The phospholipid bilayer consists of two adjacent sheets of phospholipids, arranged tail to tail. The hydrophobic tails associate with one another, forming the interior of the membrane. The polar heads (hydrophilic) contact the fluid inside and outside of the cell.

Phospholipids bilayer are thus amphipathic molecules. An amphipathic molecule is one that contains both a hydrophilic and a hydrophobic region.

Two different types of proteins that are commonly associated with the cell membrane are the integral proteins and peripheral protein.

An integral protein is a protein that is embedded in the membrane. A channel protein is an example of an integral protein that selectively allows particular materials, such as certain ions, to pass into or out of the cell.

Another important group of integral proteins are cell recognition proteins, which serve to mark a cell’s identity so that it can be recognized by other cells.

A receptor is a type of recognition protein that can selectively bind a specific molecule outside the cell, and this binding induces a chemical reaction within the cell. A ligand is the specific molecule that binds to and activates a receptor.

Some integral proteins serve dual roles as both a receptor and an ion channel.

One example of a receptor-ligand interaction is the receptors on nerve cells that bind neurotransmitters, such as dopamine. When a dopamine molecule binds to a dopamine receptor protein, a channel within the transmembrane protein opens to allow certain ions to flow into the cell.

Some integral membrane proteins are glycoproteins. A glycoprotein is a protein that has carbohydrate molecules attached, which extend into the extracellular matrix.

Peripheral proteins are typically found on the inner or outer surface of the lipid bilayer but can also be attached to the internal or external surface of an integral protein.

​​​​​​Figure- Pospholipid bilayer containing many different molecular components, including proteins and cholesterol, some with carbohydrate groups attached.

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