The original fluid mosaic model stated that membrane proteins move freely in the plane of the lipid bilayer via lateral diffusion "like protein icebergs in a sea of lipids." Since its initial description in 1927, the fluid mosaic model has been refined.
Complete the statements that describe some of the refinements of the fluid mosaic model as it relates to protein mobility.
Choose the answer that best completes each sentence:
Membrane (lipid) rafts, Vesicles, Cytoskeletal elements, Protein-protein interactions, Bilayer leaflets.
1) may form a locally rigid, non-lipid matrix surrounded by the fluid lipid matrix.
2) , membrane domains rich in sphingolipids and cholesterol, are regions with reduced lipid and protein mobility.
3) __ can be attached to proteins or can "fence in" proteins, reducing protein mobility.

The fluid mosaic model was proposed by the Singer and Nicolson in 1972 which stated that the membrane is a mosaic of the lipids, carbohydrates and the proteins.

The fluid mosaic model has been revised many times which are:

1. Protein-protein interactions: the proteins present in the lipid bilayer can easily float in the lipid layer, can be found integrated into the layer and exist on the outside of the layer. These proteins can form a bond with each other which are rigid and are non-lipid matrix.

2. Lipid rafts: the structure formed in the bilayer which is rich in cholesterol and the sphingolipids. These regions have a reduced amount of lipids and reduced protein mobility.

3. Cytoskeletal elements: are attached to the proteins and act as a fence in proteins which reduces the mobility of the proteins.