BCOR 103 1st Edition Lecture 5Outline of Last Lecture I. Introduction to the Cell MembraneII. Cell Membrane LipidsIII. Cell Membrane ProteinsIV. The Fluid Mosaic Model Outline of Current Lecture I. Introduction to Transport through a MembraneII. ChannelsIII. PumpsIV. Facilitators Current LectureMembrane 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. Voltage-gated 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