Cell Membrane 3

The picture at left is a membrane transport protein known as a sodium-potassium pump. Details are found at the "Orientations of Proteins in Membranes" (OPM) site of University of Michigan. The horizontal red and blue lines represent the cell membrane outline.

This protein, or actually set of inter-working proteins, has about 2500 amino acids. It is necessary for the cell to be able to pump out positively charged sodium particles so that the cell doesn't become too attractive to water, which can move in by osmosis and explode the cell. There are many negatively charged proteins and positive particles inside the cell, and this pump keeps the positive ion level down. The action of the pump is part of what is called active transport, when particles are moved against a gradient and/or are unable to diffuse through the membrane. More information can be found at the Wikipedia site for Sodium Pump HERE.

There are other reasons for a sodium gradient, such as stimulation of nerve cells. These cells must move ions quickly in order for them to pass a charge along their membranes from one end to the next and from one cell to another. Different cells have specialized needs and the membrane proteins must be able to handle them. Muscle cells need calcium in order to contract. Cells must move food in and waste products out, and must respond to changes in levels of hormones in the bloodstream. All these take individually specialized membrane proteins, since the rest of the membrane will not allow large proteins and food in or out.

There have been discoveries of proteins which are completely different and yet have some of the same properties. They are composed of different sets of amino acids (the building blocks of proteins), yet they fold in similar ways, which allows them to do similar work. However, folding itself is rarely found in randomly arranged amino acid sequences, as reported by protein laboratories in papers such as this by Moffet and Hecht, "De Novo Proteins from Combinatorial Libraries," Chemical Reviews 101, 10 (2001): 3191-3204. (The introduction at the title link is quite interesting). "De Novo" in the title here means, basically, new proteins. The authors were trying to figure out how to make functional proteins from the vast numbers of non-functional ones.

The calculations of the proportions of functional proteins are being worked upon now by many on both the materialistic and design advocate "sides." So far the proportions are amazingly small, such as 1 in 10^65 viable for a protein of 100 amino acids calculated by Hubert Yockey (discussed in another post HERE). Many proteins are believed to be very close to the same as they were at the very start of life because they are the ones that work. (On a different note but related: many proteins are being found unique for particular species and contribute to the species-specific features.)