Attracting Abundance

- 99 -

The Law

Belief - XI

Our Cellular Biology - X

Recall that proteins are responsible for nearly every task of cellular life. Proteins also receive signals from outside the cell and mobilize intra-cellular response. They are the workhorse macro-molecules of the cell and are as diverse as the functions they serve. Proteins can be big or small, hydrophilic or hydrophobic, exist alone or part of a multi-unit structure, and change shape frequently or remain virtually immobile. All of these differences arise from the unique amino acid sequences that make up the proteins. Fully folded proteins also have distinct surface characteristics that determine which other molecules they interact with. Not surprisingly protein structures are as diverse as the protein functions. For example, structural proteins maintain cell shape like a skeleton does for the body, and they make the structural elements in connective tissues like cartilage and bone in vertebrates. Enzymes are another type of protein, and these molecules catalyze the biochemical reactions that occur in cells. Yet other proteins work as monitors., changing their shape and activity in response to metabolic signals or messages from outside the cells. Cell also secrete proteins that are involved in inter-cellular communication.

Of special interest to us is the function of proteins in plasma (cell) membranes which typically help the cell interact with its environment. For example, plasma 

membrane proteins carry out functions as diverse as ferrying nutrients across the plasma membrane (transporter), receiving chemical signals from outside the cells (receptor), translating chemical signals into intra-cellular actions (enzymes), and sometimes anchoring the cell in a particular location (anchors). 

The overall surface of membrane proteins are mosaics, with patches of hydrophobic amino acids where the proteins contact lipids in the membrane bi-layer, and patches of hydrophilic amino acids on the surfaces that extend into the water-based cytoplasm. Many proteins can move within the plasma membrane through a process called membrane diffusion. This concept of membrane composition is called the fluid-mosaic model. A model that describes the structure of cell membranes. In simple terms, in this model, a flexible layer made of lipid molecules is interspersed with large protein molecules that act as channels through which other molecules enter and leave the cell. The portions of membrane proteins that extend beyond the lipid bi-layer into the extracellular environment are also hydrophilic and are frequently modified by the addition of sugar molecules. Other proteins are associated with the membrane but not inserted into it. They are sometimes anchored to lipids in the membrane or bound to other membrane proteins.

See the video below on cell membrane structure:

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