Question

A. What is the “Fluid Mosaic Model” of biological membranes and give an example as to why it is critical for cellular function?

B. What is homeoviscous adaptation? Why is it important for an organism? What strategies do organisms use to accomplish it?

Answer 1

The fluid mosaic model explain structure of functional cell membranes

1. The model, which was devise by SJ Singer and GL Nicolson in 1972, explain the cell membrane as a two-dimensional liquid that restricts the lateral diffusion of membrane components.
2. According to this model, there is a lipid bilayer in which the protein molecules are embedded. The lipid bilayer gives fluidity and elasticity to membrane. Small amounts of carbohydrates are also found in cell membrane
3. Membrane domains is the association of the lipid membrane with the cytoskeleton filaments and the extracellular matrix through membrane proteins.
4. Chemically a cell membrane is composed of four components -Phospholipids, Proteins, Carbohydrates, Cholesterol
5. The current model describes important features relevant to many cellular processes, including: cell-cell signaling, apoptosis, cell division, membrane budding, and cell fusion

Give an example as to why it is critical for cellular function?

1.      The fluid mosaic model was polished in the early 1980s, by two scientists called Mouritsen and Bloom to create the mattress model for membrane structure.

2.      They explain the fact that while earlier experiments had suggested that the entire membrane is fluid and allows free diffusion of proteins, there are in fact, subdomains within each membrane.

3.      For occasion, when a transmembrane protein has a hydrophobic region that is slightly longer than the average width of a cell membrane, the lipid bilayer deforms to accommodate this protein. If there are multiple proteins whose hydrophobic stretches do not exactly match membrane width, the lipid bilayer would end up looking like a mattress, with interspersed thicker and thinner regions.

4.      The wide regions would likely create a slope that lets proteins slide ‘downward’, leading to protein aggregation in some regions. Similarly, these deformations may result in the accumulation of specific lipids around those proteins.

Example

Alzheimer’s disease which cause brain shrinkage and memory loss. One thing to explaining why Alzheimer’s disease occurs is the forming of plaque sticking to the phospholipid bilayer of the brain neurons.

These plaques block communication between the brain neurons, eventually leading to neuron death and in turn causing the symptoms of Alzheimer’s, such as poor short-term memory.

What is homeoviscous adaptation? Why is it important for an organism? What strategies do organisms use to accomplish it

Homeoviscous adaptation

It is the adaptation of the cell membrane where lipid composition to make the adequate membrane fluidity.

Why is it important for an organism?

In order to maintain the of proper cell membrane fluidity is of critical importance for the function and integrity of the cell which is essential for the mobility and function of embedded proteins and lipids, diffusion of proteins and other molecules laterally across the membrane for signaling reactions, and proper separation of membranes during cell division.

What strategies do organisms use to accomplish it.

1. Eukaryotic cells group biochemical processes in organelles with characteristic surface properties and the lipid composition of organelle membranes must be tightly controlled in order to maintain organelle function and identity during adaptive responses.
2. Some highly differentiated cells such as neurons maintain unique lipid compositions with specific physicochemical properties. The sensory mechanisms regulating the acyl chain profile in such specialized cells or during adaptive responses
3. With the comparing the mechanisms of the bacterial membrane sensors with the prototypical eukaryotic lipid packing sensor Mga2 from Saccharomyces cerevisiae where membrane sensors in different organelles, organisms, and highly specialized cells.