Cell Membrane Structure and Active vs Passive Transport

Topics: Cell membrane, Endocytosis, Phospholipid Pages: 2 (435 words) Published: September 9, 2012
Discuss the structure of the plasma membrane and explain the process of active and passive transport through the membrane.

The plasma membrane is made up of proteins that form pores and channels, carbohydrate molecules that are used for cell recognition and cholesterol to provide membrane stability. Phospholipid molecules are the most abundant component found in the plasma membrane.

Phospholipids molecules are composed of a phosphate head and a lipid tail; the structure of a cell membrane is a double layer of these phospholipid molecules. The heads face out into the water solutions both inside and outside of the cell.

Proteins found within the membrane can be attached to either the inside or outside of the membrane. A form of these proteins called enzymes act as catalysts for reactions both inside and outside of the membrane. Structural proteins found within the cell membrane both support and strengthen the membrane and others anchor cell organs to the intracelleular side of the membrane. Membrane spanning proteins may act as channels or passages that control the movement of substances both in and out of the cell.

Cholesterol molecules are found in the non-polar lipid layer of the cell membrane. These cholesterol molecules make the membrane impermeable to some water soluble molecules and also help to keep the membrane flexible within a wide range of temperatures.

Active Transport within a cell membrane requires the use of energy and moves molecules from low to high concentrations using protein carriers. Types of active transport include: •Pinocytosis, in which the membrane engulfs droplets of liquids from its surroundings; •Phagocytosis, in which the membrane engulfs solid particles from its surroundings; •Receptor-mediated endocytosis, in which the membrane engufs selected molecutes that are combined with receptor proteins; •Exocytosis, in which vesicles fuse with the membrane and release contens outside of the cell; and •...
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