BCOR 103 1st Edition Lecture 5 Outline of Last Lecture I II III IV Introduction to the Cell Membrane Cell Membrane Lipids Cell Membrane Proteins The Fluid Mosaic Model Outline of Current Lecture I II III IV Introduction to Transport through a Membrane Channels Pumps Facilitators Current Lecture Membrane transport refers to moving substances across the phospholipid bilayer of a cell There are many different ways that many different substances do this successfully As discussed in the previous lecture the cell membrane is amphipathic has both hydrophilic and hydrophobic portions Most hydrophobic substances like carbon dioxide oxygen or steroid hormones can diffuse right through the membrane There are two common categories that transport can be broken into that hydrophilic substances use to move past the membrane The two categories are channels or carriers Channels are a passive form of transport and are generally used for moving ions Channels can be gated open or closed Channels do not bind molecules and are strictly a passive form of transport There are three subcategories of channels voltage gated ligand gated and mechanically gated Voltagegated channels open in response to the membrane potential or the concentration of ions on either side of the membrane An analogy for a voltage gated channel could be thinking of a room and people keep coming in and coming in Eventually there will be too many people in the room and not enough outside the room and there will be a need to open the door The difference is ions have charges and the channel is opened those ions Ligand gated channels are opened when a specific chemical i e ligand binds to the outside of the gates A perfect analogy for this channel is a key for a door A key is a ligand that opens a door Lastly mechanically gated channels are opened with a physical pull One example are the little mechanically gated channels in the ear canal When sound waves move over the hairs in the ear canal the hair bend and pull channels open inside the ear which allows an electrical signal to be sent to the brain These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Carriers are proteins that bind to and release the molecule that is being transported across the membrane There are two sub types facilitators and pumps One example of a facilitator is a uniporter transports one molecule of glucose The facilitator of glucose has two conformations that it can be in one where it is open to the outside of the membrane and the other where it opens to the cytosol When this uniporter is open to the outside of the cell it is collecting one molecule of glucose at a time Once the glucose binds to it the facilitator changes shape and deposits the glucose into the cell There are also symporters that move two or more molecules in the same direction And lastly there are antiporters which move two or more substances but in opposite directions Pumps are the second category of active transport membrane carrier Later in the course we will study more types of pumps but for now we will focus on p type or p class pumps P in p class stands for phosphorylatable P class pumps mainly move ions such as calcium sodium potassium and hydrogen P class pumps can use ATP to move ions up their concentration gradient Pumps work like this one molecule of ATP binds to the site of the pump in the cytosol an enzyme transfers the terminal last phosphate on the ATP to which powers the pump and this puts the pump in a high energy state The ions that collected on the enzyme are now transferred into the pump then pushed through the membrane