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What is a cell membrane?

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Quick Answer

A cell membrane is a thin layer that acts as a barrier that separates an individual cell or a cellular compartment from other surrounding structures. This dynamic layer plays an essential part in the transport of ions and nutrients.

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What is a cell membrane?
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A cell membrane is a complex structure made of proteins, phospholipids, cholesterol, carbohydrates and several other compounds, all of which are held in place by non-covalent forces. Each cell membrane component serves one or more essential purposes. For example, the proteins act as pumps, gates or receptors, and the lipids create hydrophobic barriers that keep aqueous compartments separate. Cholesterol increases the strength and flexibility of the membrane while also making it less permeable to aqueous compounds.

The transport across cell membranes is an essential cell function, and it depends on the layered membrane structure and the nature of the molecule to be transported. Some molecules, such as oxygen and glucose, are transported through the membrane without requiring any energy, but ions, such as sodium and potassium, are only transported actively, which means that energy is required. The cell membrane is also capable of expelling part of its contents outside through a process called exocytosis or enveloping external molecules through endocytosis. Other functions of the cell membrane include providing shape to the cell by anchoring the cytoskeleton, maintaining the cell potential and sending molecular signals to other cells.

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Related Questions

  • Q:

    What keeps cell membrane from collapsing?

    A:

    According to science writer Clare Smith for SeattlePi, the cell membrane is kept from collapsing by its phospholipid bilayer, maintenance of the correct temperature, a cytoskeleton and cell junctions. These are necessary because the cell membrane is one of the most crucial components of a cell.

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  • Q:

    Why is the cell membrane said to be selectively permeable?

    A:

    The cell membrane is said to be selectively permeable because it lets certain substances pass through while restricting the passage of others. The actual structure of the cell membrane allows free passage or restricts movement of substances across the membrane. Three ways in which the cell membrane controls the movement of substances is simple diffusion, facilitated diffusion and active transport.

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  • Q:

    What is the cell membrane made of?

    A:

    The cell membrane is comprised of phospholipids and proteins. The phospholipids are oriented so that their hydrophilic, polar heads face outwards and their hydrophobic, non-polar tails face inwards toward the middle of the cell. Proteins dot the cell membrane to allow solutes to be transported in and out of the cell membrane.

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  • Q:

    Where is the cell membrane located?

    A:

    The cell membrane is a semipermeable lipid bilayer that surrounds the cytoplasm of all cells. In animal cells, it is the outermost layer of the cell. In plants, fungi and some bacteria, a cell wall surrounds the cell membrane to form the cell's outermost layer.

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