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Transcript
General Biology Notes 9 The Cell Membrane (pages 204, 205, 208 – 213) I. The Cell Membrane A. Every cell has a _____________ ______________, which is a layer made mostly of a special type of lipid, that forms a boundary between the inside and the outside of the cell 1. __________________ also are surrounded by membrane B. The cell membrane has several _________________… 1. It controls what ___________ and leaves the cell 2. It receives signals from and sends signals to surrounding cells or the surrounding _______________________ 3. Helps maintain the cell size and _____________ C. In order to fulfill its functions, the cell membrane must be _________________ in water (so it doesn’t dissolve) but it must be willing to __________________ with water, (so it doesn’t separate from water like _________ does) D. The membrane is able to have both of these characteristics (insoluble but associates with water) because it is primarily composed of a special type of molecule called a ____________ 1. Phospholipids have a __________________ head; because the head is charged it likes _______________ (hydrophilic) 2. Phospholipids have a tail, made of fatty acid chains, that is ______________ (also called nonpolar); because they are not charged they dislike water (_________________) E. In a watery environment phospholipids will form a _____________________ ________________ 1. Two layers of the lipids joined neutral tail to tail, with the _____________ portion of the molecule facing outwards from the cell or inwards, where there are watery environments F. The membrane is also composed of proteins and to a lesser extent carbohydrates 1. Proteins a. Many types of proteins aid in ________________ of substances across the membrane (see II C below) b. Some proteins stick out from the membrane into the surrounding environment and help the cell sense ______________ in the environment and help the cell to ____________________ with other cells 2. ________________________ in the membrane are also used in cellular communication II. Movement across the membrane A. The cell membrane is designed so that it allows certain things to pass through, while restricting the passage of other things 1. This property is called ___________________ ________________________ Please turn over B. Some small molecules, such as H2O, O2 and _______ can freely pass through the membrane 1. These molecules are ________________ enough to squeeze between the much bigger phospholipids of the membrane 2. Free movement between the phospholipids, from an area of high concentration to an area of low concentration, is called ___________ ______________ 3. To understand how passive transport works, one must understand the process of ________ a. Diffusion is the natural tendency of solutes to move from an area where they are _______________ concentrated to an area where they are less _________________ b. This is a very important process because, as we will see, it is largely responsible for getting __________ and _____________ into the cell, and getting ______________ (including CO2) out C. ________________ are also found in the membrane forming holes and gates, which open and close when needed 1. ________________ and larger molecules (for example _______________________ or amino acids) cross the membrane through these gates or holes a. Movement from an area of high concentration to an area of low concentration through these proteins is called _______________ __________________ b. Proteins can also use energy to move substances from where they are in low concentration to where they are in high concentration; this is called ________________ _______________ III. Water and the membrane A. Water movement by itself is important because cells must stay ___________________, but there are also times when cells must export water 1. Water moves by _____________________ 2. The special situation of water moving across a permeable barrier (a ________________) by diffusion is called _______________ a. Water flows according to ________________, from areas where it is _______________ concentrated to areas where it is in __________ concentration b. What determines water concentration is solute concentration i. Where __________ are in high concentration ___________ is in low concentration, and vice versa i. Example - solute concentration inside the cell is 50 micrograms/1000 ml - solute concentration outside of the cell is 25 micrograms/1000 ml - where solute is low (25<50) water is high, so water will flow _______________ the cell 3. Since water concentration in part determines solute concentration, water also influences the ____________________ _______________ and _____________________ ______________ of solutes