Cell Parts Definitions-The outer surface of each cell is limited by the smooth and elastic membrane called the cell membrane. This membrane is very important in the regulation of cell contents, because all the ingredients that go out or enter must pass through this membrane. This means, cell membrane prevents the entry of certain substances and facilitate the entry of other substances. In addition to restricting cell, plasma membrane also limits the various organelles within the cell, such as the vacuole, mitochondria, and chloroplasts.
The plasma membrane is permeable differential, having ultra microscopic pores through which certain substances. The pore size determines the maximum large molecules can pass through the membrane. In addition to large molecules, other factors that affect the entry of a substance into the cell is an electric charge, the number of water molecules and particles in the water solubility.
The cell membrane is composed of two layers of phospholipid molecules (fat combines with phosphate). The tail of the fatty acid hydrophobic (nonpolar), the second layer are mutually oriented molecules into.
Meanwhile, the head of the hydrophilic (polar) leads to a watery environment. In addition there is also a glycolipid phospholipid (fat fused with carbohydrates) and sterol (especially cholesterol fatty alcohol).
Meanwhile, the components located on the membrane proteins with different positions. Some proteins located peripheral, while others are embedded in the integral double layer of phospholipids. Some membrane proteins are enzymes, while others are receptors for hormones or certain other compounds. The composition of the membrane lipids and proteins constituent varies, depending on the type and function of the membrane itself. However, the membrane has the same characteristics, which are selectively permeable to molecules. Thus, the cell membrane can maintain cell shape and size.
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