Exam 1 will be held Friday Oct 2nd in the Tes9ng Center Arjona 110 You must sign up for an available Exam Slot on HuskyCT Exam Registra9on Link Exam slots 11 12 30 12 30 2 2 00 3 30 3 30 5 there is no regular class on exam day If you have another class con ict with the available slots you must provide a screenshot of your UConn schedule and contact me ASAP There will be 2 Review sessions before the Exam 1 Wednesday 9 30 6 8pm TLS 154 2 Thursday 10 1 6 8pm Arjona 143 Bring your Problem Sets The early exam for people with legi9mate reasons that have been cleared with me will be on Thursday 10 1 Time Place TBA If you need to take the early exam for a legiMmate reason and have NOT contacted me yet please do so ASAP david daggeR uconn edu Students who have CSD Exam 9me place accommoda9ons will be taking the exam at the CSD o ce Please get any Exam AdministraMon Forms to me ASAP MCB 2210 Exams will be taken at the Tes9ng Center Rm 110 Arjona On each scheduled Exam day there will be mulMple Mme periods to take the exam Prior to the Exam you must follow the Exam RegistraMon link on the Husky CT site to sign up for one of the periods They will be lled rst come rst serve Exams will be taken on computer terminals at the TesMng Center You must arrive at 110 Arjona at least 10 minutes before the exam period You must have your UConn ID with you to sign in You may only bring a pen or pencil to the computer terminal and scratch paper will be provided At the start of the Exam Period you will be given a password to access the Exam via the MCB 2210 HuskyCT site The password will allow you access to the Exam only once and the exam must be completed by the end of the Exam period Membrane Transport Permeability proper9es of the plasma membrane The plasma membrane and its proteins funcMon as a selecMve permeability barrier Molecules di use across the membrane at di erent rates Some are able to move through the lipid bilayer more easily than others based upon their chemical properMes For those that cannot easily cross the membrane there are transporters in the membrane to control their entry Small uncharged molecules can move across the lipid bilayer by passive di usion Passive di usion is when molecules di use directly through the lipid bilayer no protein involvement Some molecules di use through easily Small uncharged non polar Gasses O2 CO2 cross easily Small uncharged polar such as H20 Urea cross but slowly The rate is much slower as molecules get larger or more polar or charged Sugars Amino Acids very slow Ca2 K Na Cl e ecMvely impermeable Proteins not at all Rate of movement is directly related to solubility of molecule in lipid bilayer parMMon coe cient The more soluble a molecule is in the lipid bilayer the faster it will di use across Membrane Transport Proteins The soluMon to the limited permeability of the membrane for some substances is for cells is to have transport proteins in their membranes These proteins are enzymes that catalyze movement of speci c substances across the membrane Passive Transport Passive transporters allow net movement down a chemical concentraMon electrical or electrochemical gradient they require no energy beyond thermal moMon facilitated di usion by uniporter carrier proteins Ion Channels Ac9ve Transport AcMve transporters can move molecules against a chemical electrical or electrochemical gradient they require extra energy input for transport ATP dependent pumps Symporter a k a co transporter carrier proteins AnMporter a k a exchanger carrier proteins Passive vs Ac9ve Transport Channels vs Carriers Kine9cs of Transport Unlike simple di usion facilitated di usion by carrier proteins can be saturated due to binding of solute to carrier Di usion doesn t peak No saturaMon Transport peaks when binding sites on transporter are saturated Cells use transport proteins to generate an internal ionic environment that is di erent than the external environment and to exploit the resul9ng gradients to perform cri9cal func9ons Ion Outside mM Cytoplasm mM Membrane Permeability Na 140 14 variable K 5 145 high Ca2 2 0 0001 variable Cl 145 8 some Biochem z 1 2 0 125 NO WAY The ionic composiMon is not the same inside and out Total caMons and anions are equal electroneutrality Total number of parMcles inside and out is equal osmolarity is the same Based on typical complement of transporters Lipid bilayer itself impermeable to these The importance of maintaining ICF osmolarity equal to that of the ECF Ions and electrochemical gradients For uncharged molecules like glucose transport is simply based upon concentraMon gradient For ions charge adds another force If the inside of the cell has a net negaMve charge a negaMve ion anion will be repelled and a posiMve ion caMon will be aRracted If the inside has a net posiMve charge an anion will be aRracted and a caMon repelled The combinaMon of the chemical concentraMon gradient and the electrical gradient determines the rate and direcMon of transport of a charged molecule This is known as the Electrochemical Gradient Electrochemical Gradients Di usion of ions gives rise to electrical poten9als 125 As K ions ow out Cl ions that helped maintain charge balance are ler behind These Cl ions distribute themselves beneath the membrane aRracted to caMons outside They exert a force across the membrane That force is an electrical potenMal the membrane poten9al Vm When the density of negaMve charges increases enough it exerts a negaMve inside electrical force that is su cient to counter the concentraMon gradient K ions stop owing out current shown rt Only a relaMvely few K ions 001 of the total have to ow out to leave behind enough Cl ions to generate the electrical force The concentraMons don t appreciably change A very small number of ions need to move to create the membrane poten9al Concentra9on essen9ally unchanged left to right Di usion of ions gives rise to electrical poten9als 125 As K ions ow out Cl ions that helped maintain charge balance are ler behind These Cl ions distribute themselves beneath the membrane aRracted to caMons outside They exert a force across the membrane That force is an electrical potenMal the membrane poten9al Vm When the density of negaMve charges increases enough it exerts a negaMve inside electrical force that is su cient to counter the concentraMon gradient K ions stop owing out current shown rt Only a relaMvely few K ions 001 of the total have to ow out to leave behind enough Cl ions to generate the electrical force