Plant Cell Structures: The cell membrane and cell wallPlant cells are the fundamental unit of structure in most plants. And two of the most vital cell structures are the cell membrane and cell wall.The Cell Membrane
The cell membrane, also referred to as plasma membrane, is a semi-permeable lipid membrane. It contains lipids, biological molecules and proteins which help in the cellular processes.
The cell membrane acts as a separator or a skin that separates the extracellular environment from the intracellular components. The skin-like membrane can regulate substances that enter and exit the cell. Substances can move through the membrane passively (no cellular energy required) or actively (requiring cellular energy).
Certain proteins within the cell membrane function as signals to allow cells to interact. All throughout the cell membrane, protein receptors are found and function as signal receptors from other cells and from the environment. Other proteins on the cell membrane’s surface function as markers.
Cell membrane structure:
Integral membrane proteins are found all throughout the cell membrane surface. These can be viewed by an electron microscope or fluorescence microscope. These proteins include desmosomes, caveolaes, clathrin-coated pits, synapses and other structures that are vital for cell adhesion.
The cell membrane contains a cytoskeleton that also serves as an anchor for forming organelles and other proteins. The cytoskeleton can form limb-like organelles that develop from the cell’s surface are covered by the cell membrane. These limb-like extensions of the cell are called microvilli and they increase the cell’s surface area which in turn increases nutrient absorption.
The fluid mosaic model of Singer and Nicholson states that biological membranes could be made up of two-dimensional fluid where protein and lipid molecules can diffuse less or more freely. But plasma membranes contain various structures such as protein complexes, actin-based cytoskeleton, lipid drafts and either desmosomes or synapses.
The cell membrane is composed of three types of amphipathic lipids namely phospholipids, steroids and glycolipids. Composition of each type vary from one cell type to another, but in most cases the phospholipids are more predominant.
Fatty acid chains found in glycolipids and phospholipids normally equal in number, around 14 to 24. These fatty acids may be unsaturated or saturated. Unsaturation degree and length usually affects the fluidity of the membranes.
Hydrophobic tails which held the entire cell membrane is quite fluid. The fluidity of the cell membrane is attributed to the phospholipids molecules allows it to freely diffuse.
The protein content of a typical cell membrane is about 50%. Proteins are quite vital for cell development and function. There are three membrane proteins namely integral proteins, lipid anchor proteins and peripheral proteins.
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