Transporting molecules across cell membranes Nutrients, wastes, hormones, ions
Recall phospholipid bilayer It s a barrier! Only a small subset of molecules may pass through without help
Cell membrane Sense & respond to changes in environment Regulate exchange with environment
Cell membranes are selectively permeable Some compounds pass uninhibited through membrane (passive diffusion), some require assistance from membrane proteins (facilitated diffusion), and some require assistance AND energy expenditure (active transport) 1. Diffusion Passive transport or diffusion Carrier-mediated (facilitated) transport or diffusion 2. Active Transport Pumps, bulk transport
PM + proteins mediate transport Passive (Diffusion & Osmosis) or Active Simple diffusion; P Carriermediated; A or P Channelmediated; P Osmosis; P
Proteins are responsible Some are receptors that regulate bulk transport Induce endocytosis or exocytosis Cyto from kyto = hollow vessel
Concept Check Membranes organize cell activities. The proteins imbedded in the membranes are essential to their function. These membrane proteins have properties that allow them to float in the membrane. Which of the following describe those properties? a) The surface region of the protein in the interior of the membrane is mostly hydrophobic. b) The surface region of the protein in the interior of the membrane is mostly hydrophilic. c) The surface region exposed to the exterior environment is hydrophobic. d) The surface region exposed to the interior environment is hydrophobic.
Answer Membranes organize cell activities. The proteins imbedded in the membranes are essential to their function. These membrane proteins have properties that allow them to float in the membrane. Which of the following describe those properties? a) The surface region of the protein in the interior of the membrane is mostly hydrophobic.
So, what is diffusion? Solvent: The predominant liquid or gas in a solution Solute: The stuff that is dissolved in a solution Diffusion: The net movement of solute from a higher to a lower concentration (Concentration gradient), until equilibrium is achieved. Uses intrinsic Kinetic Energy (KE).
Everything has Energy Energy = The capacity to perform work; to rearrange matter 2 forms: Potential Energy (PE): stored energy, due to position or structure Kinetic Energy (KE): Energy of motion Heat is KE associated with the movement of molecules/atoms
Passive Diffusion
Passive Diffusion
Passive diffusion Kinetic energy causes particles to move Diffusion occurs due to random collisions between these moving particles
Osmosis Passive diffusion of H 2 0 down its concentration gradient Due to solutes inside flask, there s more H 2 0 outside than in Only H 2 0 can pass through pores H 2 0 moves down its concentration gradient and INTO flask
Osmosis + Diffusion Both are happening all the time across cell membranes Osmosis (H 2 0) occurs RAPIDLY, diffusion (solutes) occurs SLOWLY H 2 0 moves into cells with high solute concentration and out of cells with low solute concentration
What happens? If you place a cell into a solution whose solute concentration is much lower than that of the cell, what will happen to the cell? Will it: 1. Shrink (crenate; as H 2 0 leaves) 2. Swell (as H 2 0 enters) 3. Remain unchanged
Concept Check This diagram represents osmosis of water across a semipermeable membrane. The U-tube on the right shows the results of the osmosis. What could you do to level the solutions in the two sides of the right hand U-tube? a) Add more water to the left hand side. b) Add more water to the right hand side. c) Add more solute to the left hand side. d) Add more solute to the right hand side.
Answer This diagram represents osmosis of water across a semipermeable membrane. The U-tube on the right shows the results of the osmosis. What could you do to level the solutions in the two sides of the right hand U-tube? c) Add more solute to the left hand side.
Tonicity Tonicity: measure of the solvent concentration of a solution and it s osmotic pressure Hypertonic: Solute concentration is greater than the cytoplasm = net movement of H 2 O out of cell Hypotonic: Solute concentration of solution is less than the cytoplasm = net movement into cell Isotonic: Solute concentration of solution is equal to the cytoplasm = no net movement of H 2 0
Cells in different solutions
Facilitated diffusion Diffusion can be simple or facilitated Facilitated is Passive No energy needed to move molecules. Molecules move down their concentration gradient
Active transport 1. requires ATP (energy) to move molecules. 2. Molecules move against their concentration gradient.
Maintains gradient for cotransport
Endo- & Exocytosis Bulk transport; A Requires ATP Phagocytosis: ingestion of solid particles phagein = to eat Pinocytosis: ingestion of liquid
Active; Requires ATP Endocytosis
Active; Requires ATP Exocytosis