MEMBRANE STRUCTURE AND FUNCTION

REVIEW QUESTIONS Another term for cell membrane is ________ What is the function of the membrane? What does the term ‘partially permeable’ mean? What is the size of the cell membrane? Are cell membranes visible with the light microscope? What is the name of the component that makes up the double layer? What is the difference between hydrophilic and hydrophobic? Name 5 functions of membranes and one example of each Different proteins make up the cell membrane. What are the different categories of these proteins? What is the function of these proteins? How are proteins able to stay within the membrane? List the names of the components of cell membranes and the role of each component. What does the fluid mosaic model refer to?

I like to MOVE IT, MOVE IT! Many substances pass through the plasma membrane itself. These substances move passively or actively through the cell. PASSIVE MOVEMENT ACTIVE MOVEMENT No energy needed for movement Uses energy (ATP) to make substances move up their concentration gradients Diffusion Facilitated diffusion Osmosis

DIFFUSION Diffusion is the net of molecules down their concentration gradient Random movement of particles Small uncharged particles are easily slipped through the phospholipid layer Small molecules are more likely to get through Diffusion ability affected by ionic charge

FACILITATED DIFFUSION Cells provide special pathways through the plasma membrane which allow ions to pass through Pathways are provided by channel proteins which lie in the membrane stretching from one side to the other. Forming a hydrophilic channel which ions can pass through The only way in which molecules or ions can get through the membrane is if they bump into a channel Each channel allows only a specific ion or molecule to pass through Antiports allow movement in two directions Symports allow movement in one direction The protein can change its shape opening or closing the channel Substances can move either direction Antiports and symports can be involved in active transport

FACILITATED DIFFUSION

ACTIVE TRANSPORT

EXOCYTOSIS

ENDOCYTOSIS

OSMOSIS

OSMOSIS DEFINITION: Movement of water molecules down their diffusion gradient, through a partially permeable membrane. Symbol for water potential: ψ (psi) The water potential of a solution is a measure of how much water the solution contains in relation to other substances, how freely the water molecules can move and how much pressure is being applied to it. It can be thought of as the tendency for water to leave a solution. SOLUTION WITH A LOT OF WATER: High water Potential SOLUTION WITH LITTLE WATER AND NOT UNDER PRESSURE: Low water Potential

OSMOSIS Water potential of 0 More solute you dissolve in the water PURE WATER Water potential of 0 WHEN YOU ADD SOLUTE More solute you dissolve in the water The lower its water potential gets Freedom of water molecules is reduced because they are attracted to the solute molecules Therefore a sugar solution has a water potential of less than zero (a negative value)

OSMOSIS Water tends to move DOWN a water potential gradient. A LOT OF WATER PRESENT HIGH WATER POTENTIAL LESS WATER PRESENT LOW WATER POTENTIAL