Of What Is The Cell Membrane Composed – This simple, cutaway model of an animal cell (Figure (PageIndex)) shows that a cell looks like a plastic bag full of Jell-O. Its basic structure is a plasma membrane filled with cytoplasm. Like Jell-O with mixed fruit, the cytoplasm of the cell also contains various structures, such as a nucleus and other organelles. Your body is made up of trillions of cells, but they all perform the same basic life functions. They all get and use energy, react to the environment and reproduce. How do your cells perform these basic functions and keep themselves—and you—alive? To answer these questions, you need to know more about the structures that make up cells, starting with the plasma membrane.
The plasma membrane is a structure that forms a barrier between the cytoplasm inside the cell and the environment outside the cell. Without the plasma membrane there would be no cell. The membrane also protects and supports the cell and controls everything that goes in and out of it. It only allows certain substances to pass while keeping others in or out. To understand how the plasma membrane controls what goes into or out of the cell, you need to know its basic structure.
Of What Is The Cell Membrane Composed
The plasma membrane is mainly composed of phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a phospholipid bilayer, with a hydrophobic, or water-hating, interior and a hydrophilic, or water-loving, exterior. Each phospholipid molecule has a head and two tails. The head “loves” water (hydrophilic) and the tails “fear” water (hydrophobic). The water-fearing tails sit on the interior of the membrane, while the water-loving heads point outward, towards the cytoplasm or the fluid that surrounds the cell. The polar head group and fatty acid chains are attached by a 3-carbon glycerol unit. Image (PageIndex) shows a single phospholipid next to a phospholipid bilayer.
Plant Cell Wall: Structure, Functions, Diagram
Molecules that are hydrophobic can easily pass through the plasma membrane if they are small enough because they are hydrophobic like the interior of the membrane. Molecules that are hydrophilic, on the other hand, cannot pass through the plasma membrane – at least not without help – because they are hydrophilic like the outside of the membrane.
The plasma membrane also contains other molecules, mainly other lipids and proteins. The green molecules in figure (PageIndex), for example, are the lipid cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane maintain its shape. (Figure (PageIndex)) shows the cholesterol molecules as yellow structures within the center of the phospholipid bilayer. Other structures shown in (figure (PageIndex)):
The plasma membrane can have extensions, such as whip-like flagella or brush-like cilia, which give it other functions. In unicellular organisms, such as the one shown below, these membrane extensions can help the organisms move. In multicellular organisms, the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus to the mouth and nose.
Image (PageIndex): Flagella of Giardia (left) and cilia of human respiratory mucosa (right). Flagella and cilia are extensions of the plasma membrane of many cells.
Cell Membrane Function And Structure
If you smoke and need another reason to quit, here’s a good one. We usually think of lung cancer as a major disease caused by smoking. But smoking can have devastating effects on the body’s ability to protect itself against repeated, serious respiratory infections, such as bronchitis and pneumonia.
Cilia are microscopic, hair-like projections on cells that line the respiratory, reproductive, and digestive systems. Cilia in the respiratory system line most of your airways where they have the job of trapping and removing dust, germs and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward to the throat, where they can be expelled from the body. If you are sick and coughing up phlegm, that’s what you do.
Smoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they cannot sweep mucus from the airways and they also inhibit the cilia from producing mucus. Fortunately, these effects begin to wear off soon after the last exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will grow back and function again in a matter of months after you stop smoking.
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B: Gram Negative Outer Membrane
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Membrane, in biology, the thin layer that forms the outer boundary of a living cell or of an internal cell compartment. The outer boundary is the plasma membrane, and the compartments enclosed by internal membranes are called organelles. Biological membranes have three primary functions: (1) they keep toxic substances out of the cell; (2) they contain receptors and channels that allow specific molecules, such as ions, nutrients, waste products, and metabolic products, that mediate cellular and extracellular activities to pass between organelles and between the cell and the external environment; and (3) they separate vital but incompatible metabolic processes carried out within organelles.
Membranes consist mainly of a lipid bilayer, which is a double layer of phospholipid, cholesterol and glycolipid molecules that contains chains of fatty acids and determines whether a membrane is formed in long flat sheets or round vesicles. Lipids give cell membranes a fluid character, with a consistency that approaches that of a light oil. The fatty acid chains allow many small, fat-soluble molecules, such as oxygen, to pass through the membrane, but they repel large, water-soluble molecules, such as sugar, and electrically charged ions, such as calcium.
The cell membrane contains proteins that transport ions and water-soluble molecules into or out of the cell. Some molecules can freely diffuse across the membrane in a process known as simple diffusion.
Cell Membrane (plasma Membrane)
Embedded in the lipid bilayer are large proteins, many of which transport ions and water-soluble molecules across the membrane. Some proteins in the plasma membrane form open pores, called membrane channels, which allow the free diffusion of ions in and out of the cell. Others bind to specific molecules on one side of a membrane and transport the molecules to the other side. Sometimes one protein transports two types of molecules in opposite directions at the same time. Most plasma membranes are about 50 percent protein by weight, while the membranes of some metabolically active organelles are 75 percent protein. Long carbohydrate molecules are attached to the proteins on the outside of the plasma membrane.
Many cellular functions, including the absorption and conversion of nutrients, synthesis of new molecules, production of energy, and regulation of metabolic sequences, take place in the membrane organelles. The nucleus, containing the genetic material of the cell, is surrounded by a double membrane with large pores that enable the exchange of materials between the nucleus and cytoplasm. The outer nuclear membrane is an extension of the membrane of the endoplasmic reticulum, which synthesizes the lipids for all cell membranes. Proteins are synthesized by ribosomes that are either attached to the endoplasmic reticulum or suspended freely in the cell contents. The mitochondria, the oxidizing and energy-storing units of the cell, have an outer membrane that is easily permeable to many substances, and a less permeable inner membrane studded with transport proteins and energy-producing enzymes. membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside vironmt (the extracellular space).
The cell membrane consists of a lipid bilayer, made up of two layers of phospholipids with cholesterols (a lipid component) interspersed between them, and maintains appropriate membrane fluidity at different temperatures. The membrane also contains membrane proteins, including integral proteins that span the membrane and serve as membrane transporters, and peripheral proteins that attach loosely to the outside (peripheral) side of the cell membrane, act as zymes to interact with the vironmt of to facilitate the cell.
Glycolipids embedded in the outer lipid layer serve a similar purpose. The cell membrane controls the movement of substances into and out of a cell, and is selectively permeable to ions and organic molecules.
What Is A Cell?
In addition, cell membranes are involved in a variety of cellular processes such as cell adhesion, ion conductivity and cell signaling and serve as the attachment surface for various extracellular structures, including the cell wall and the carbohydrate layer called the glycocalyx, as well as the intracellular network of protein fibers called the cytoskeleton. In the field of synthetic biology, cell membranes can be artificially reassembled.
While Robert Hooke’s discovery of cells in 1665 led to the
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