Lecture 8 Membrane Transport Carrier mediated Transport o 2 Active Transport 1 30 15 uses transmembrane proteins Figure 4 11 Almost always against gradient associated with an energy cost Based on conformation changes and ATP 1 Primary Active Transporter uses ATP directly They are transport proteins o Aka ATPase pumps Breaks down ATP to create a gradient o Equation number 1 ATP ADP P Example Sodium Potassium ATPase pump o Sodium goes out of the cell potassium goes in o Steps ATP binds conformation change 3 sodium binds hydrolysis of ATP now only a P is bound to the protein and the ADP floats away orientation flip sodium is released 2 potassium bind release P orientation flip release of potassium Higher concentration of Na outside of cell and higher concentration of K inside cell A new ATP can bind later and start the cycle all over again Know how this happens step by step SUPER IMPORTANT It is a 10 step process note I added an extra step on my own for clarification o Why do we want to create these gradients o Because it creates potential energy Allows for secondary active transport 2 Secondary Active Transporter uses ATP indirectly Uses energy in an actively established ion gradient to move a 2nd molecule against its gradient One compound moves with its gradient and one compound moves against its gradient 1 30 15 o The one moving with its gradient powers the one moving against its gradient ATP is used to create the gradient for the one compound This is how we get glucose into our cells in the digestive track o Terminology Cotransport same direction ex both move into the cell Countertransport opposite direction ex one moves in the cell the other moves out of the cell o Note we are size limited we can only moves things smaller than the protein transporter in out of the cell o So how do we move large things We use Vesicle Formation o Figure 4 20 o Moves large compounds very high energy cost o Require ATP and cholesterol o Cholesterol is important because for stiffening the membrane It s like tossing a water balloon If it is very fluid it is very easy for it to slip through your hands But if it is stiffer like a basketball it will be easier to catch o Endocytosis In fold of membrane Contains Interstitial fluid part of the extracellular fluid Forms intracellular membrane bound vesicles o Exocytosis Fusing with membrane Releasing contents to Interstitial fluid o Functions of Endocytosis Transcellular transport figure 4 21 We do this because we cant go around the cell if there are tight junctions present so we have to go through the cell to get thing to the other side Especially in epithelial cell since they are rich in tight junctions Endosomal Processing Where a vesicle is brought into the cell so that its internal contents can be modified Destroying engulfed material Process used by the immune system Recycling the membrane 1 30 15 Need to balance endocytosis with exocytosis so the cell size doesn t change too drastically Figure 4 21 o Functions of Exocytosis Replace recycled membrane Chemical messenger release Important for endocrines paracrines and neurotransmitters We can release intracellular chemical messengers that are too large to pass through the membrane to promote cell to cell communication o Stimulus Receptor afferent integrating center efferent Cellular Communication Recall the reflex arc effector physiological response o This is at the cellular level Cell or larger Where are signal being passed o Communication is happening in our afferent and efferent pathway o We can also see communication within out integrating center effector and sometimesssss receptor Key terminology o At the molecular level proteins and ligands the terminology changes o Messengers signals something also called ligands o Receptors proteins that the ligands bind to When a ligand binds this means communication has occurred Problem Wtf Our receptor is a ligand releaser Our effector acts as a receptor How do you know which one we are talking about Pay attention to context ex phat Receptor Characteristics Activation ligand binds o Based on shape and charge Specificity limited binding o Figure 5 2 o Digital type of response it either has specificity or it doesn t It either will bind or it will not bind Dependent on shape AND charge o Specificity is saying the ligand and receptor match o You can only talk about the degree of activation once you have specificity Affinity strength of binding o Figure 3 29 o High affinity high match in shape AND charge o Analog there is a range of affinity low medium high o Percent activation is related to affinity 1 30 15 o Specificity has to happen before we ask the affinity question If you have high specificity you do not necessarily have high affinity If you have affinity you already have specificity If there is no specificity there is not affinity
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