Nicolson proposed a new model that provides microscopic observations and better explains plasma membrane function. In the 1950s, advances in microscopy, notably transmission electron microscopy (TEM), allowed researchers to see that the plasma membrane’s core consisted of a double, rather than a single, layer. They made the analogy of proteins to bread, and lipids to the filling. Davson and Danielli theorized that the plasma membrane’s structure resembles a sandwich. It was based on the plasma membrane’s “railroad track” appearance in early electron micrographs. This was the first model that others in the scientific community widely accepted. In 1935, Hugh Davson and James Danielli proposed the plasma membrane’s structure. The principal components they identified were lipids and proteins. Scientists identified the plasma membrane in the 1890s, and its chemical components in 1915. Occasionally, viruses hijack receptors (HIV, human immunodeficiency virus, is one example) that use them to gain entry into cells, and at times, the genes encoding receptors become mutated, causing the signal transduction process to malfunction with disastrous consequences. These membrane receptors provide extracellular attachment sites for effectors like hormones and growth factors, and they activate intracellular response cascades when their effectors are bound. These proteins act both as extracellular input receivers and as intracellular processing activators. In addition, the plasma membrane’s surface carries markers that allow cells to recognize one another, which is vital for tissue and organ formation during early development, and which later plays a role in the immune response’s “self” versus “non-self” distinction.Īmong the most sophisticated plasma membrane functions is the ability for complex, integral proteins, receptors to transmit signals. These are the more obvious plasma membrane functions. The plasma membrane must be very flexible to allow certain cells, such as red and white blood cells, to change shape as they pass through narrow capillaries. Cells exclude some substances, take in others, and excrete still others, all in controlled quantities. Identify components of the cell membrane, including phospholipids, cholesterol, proteins, and carbohydratesĪ cell’s plasma membrane defines the cell, outlines its borders, and determines the nature of its interaction with its environment.Describe the structure of cell membranes.
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