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Definition
| A protein responsible for mediating the active transport of molecules from one side of the lipid bilayer to the other. Transport is carried out by a conformational change that occurs within the protein that forms an opening for specific molecules to pass through. |
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| The transport of molecules across a membrane and against their natural flow; mediated by carrier proteins and requiring outside energy. |
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| A protein responsible for mediating the passive transport of molecules from one side of the lipid bilayer to the other. Transport is carried out by its membrane-spanning hydrophilic structure which, when open, allows molecules to pass through. |
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| The transport process in which molecules naturally travel from an area of higher concentration to an area of lower concentration. |
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| A layer of carbohydrates that coats the exterior of higher-ordered cells. Functions in protecting the cell from damage. |
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| A polar molecule that selectively associates itself with water through hydrogen bonds. |
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Definition
| A nonpolar molecule that does not readily associate with water through hydrogen bonds. |
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Definition
| A membrane protein that cannot be easily removed from the lipid bilayer. |
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| A class of membrane transport proteins. Small, hydrophobic molecules that increase membrane permeability to certain ions. |
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Definition
| A thin double layer of phospholipid molecules. Provides the structure of a cell membrane. Structure is a result of hydrophobic and hydrophilic forces. |
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Definition
| Membrane proteins that are located entirely within the lipid bilayer, having no part touching either the inside or outside of the cell |
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Definition
| Transmembrane proteins that cross the lipid bilayer more than one time. |
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Term
| What is the main function of the lipid bilayer? |
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Definition
| The lipid bilayer acts as a barrier between the inside and outside of the cell. It is highly impermeable and does not allow most molecules to freely pass through it into or out of the cell. |
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Term
| Why is the structure called a lipid bilayer? |
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Definition
| It is called a lipid bilayer because it is composed of two layers of fat, or lipid, molecules. |
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Term
| What are the regions in the phospolipid molecule? |
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Definition
| A phospholipid molecule contains two distinct regions. The Hydrophilic region is attracted to water and the Hydrophobic region is repelled from water. As a result of its both polar and nonpolar regions, it is classified as an Amphipathic molecule. |
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Term
| Are the two layers of the lipid bilayer identical in composition? |
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Definition
| No. As a result of the bilayer's fluidity, structures such as lipids and proteins can freely move around within the lipid bilayer. |
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Term
| Will you find the same set of membrane proteins in each cell membrane? |
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Definition
| No. Membrane proteins perform a number of functions within cells, as a result, different proteins are necessary in different regions of cells depending on the function of the cell and the interactions it may take part in. |
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Term
| What are the names of the two main classes of membrane proteins and how could you tell one from the other? |
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Definition
| The two main classes of membrane proteins are integral versus peripheral proteins. Since peripheral proteins are easily dissociated from the lipid bilayer, one could treat a cell with a mild detergent that does not disrupt the cell membrane and then see if the specific protein remains associated with the lipid bilayer or is removed. |
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| What is the name of the configuration that membrane proteins adopt in regions that span the lipid bilayer? |
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Definition
| This configuration is called an alpha-helix. It is the same structure that DNA adopts naturally. |
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Term
| Which class of proteins, integral or peripheral, are freer to move around within the lipid bilayer? |
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Definition
| Integral proteins can be thought of as icebergs that float in a lipid bilayer sea. They are relatively mobile in the cell membrane. |
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Term
| The cell surface is covered with an additional set of molecules. What name is given to these structures and what is their function in the cell? |
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Definition
| The cell surface is covered with a cell coat or glycocalyx which consists of carbohydrate chains. They help protect the cell from damage. |
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| Why is it necessary for cell membranes to have proteins that help transport molecules? |
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Definition
| The cell membrane is composed of a lipid bilayer that is highly impermeable to most molecules. As a result, outside structures are required to help transport essential large, polar molecules across the cell membrane. |
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Term
| What is the name of the natural process by which molecules flow from an area of higher concentration to one of lower concentration? |
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Definition
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| What is the difference between the behavior of carrier and channel proteins? |
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Definition
| Carrier proteins allow specific molecules to cross the cell membrane by undergoing a conformational change upon the binding of the molecule. The conformational change opens a hole through which the molecule can enter or exit a cell. Channel proteins do not require the binding of a molecule and conformational change to open. Channel proteins allow molecules to steadily diffuse across the membrane through diffusion. |
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Term
| What is the function of an ionophore? |
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Definition
| Ionophores function to increase a membrane's permeability to a specific ion thereby facilitating its movement across that cell's membrane. |
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| Name two specific functions of membrane transport |
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Definition
| Membrane transport helps maintain the proper distribution of ions across a cell membrane; helps maintain proper cellular pH, and helps mediate communication between cells in multi-cellular organisms. |
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