BIO250 Spr11-25

BIO250 Spr11-25 - BIO250 BIO250 Introduction to...

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BIO250 BIO250 Introduction to Biochemistry Introduction to Biochemistry March 23: Membranes March 23: Membranes -Flexibility and Dynamics -Flexibility and Dynamics N
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Today’s agenda Administrative issues Membrane structure revisited Measuring membrane dynamics Membrane dynamics depends on temperature Question to ponder The fluid mosaic model of membranes Membranes are asymmetric
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Administrative Issues
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Announcements Exam #2 has been returned Q2P from last time will be discussed towards the end of this lecture Blackboard issue: make sure that your survey votes are recorded (checkmark under “My Grades”) in the Grade Center. My availability next week will be limited. No office hours next week. If you want to meet in person next week, make an appointment by noon on Friday. I will monitor Blackboard daily
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Membrane structure revisited
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A simple membrane: a bilayer of phosphatidyl choline N
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Phosphatidylcholine N choline Glycerol + 2xFA phosphate
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Phosphatidyl choline is in constant motion: an animation Entire sequence corresponds to 500 picoseconds = 0. 5 nanoseconds = 0.5 * 10 seconds N
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As a result, the interior of a membrane is a bit chaotic X N
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X As a result, the interior of a membrane is a bit like a bowl of spaghetti
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Compare that to lecture 7 in proteins, the exact 3D structure is crucially important lock and key for enzyme/substrate assembly of hemoglobin into a tetramer changing even a single contact can have dramatic consequences: sickle cell anemia
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The Deoxyhemoglobin Heterotetramer: α 2 β 2 Fig. 4-22 β α α β N
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Subunit Contacts in Hemoglobin Strong hydrophobic interactions occur between unlike subunits There are also many hydrogen bonds and a few ion pairs Those between α 1 β 1 involve > 30 residues, are stable in urea to give an α 1 β 1 dimer The α 1 β 2 dimer interface involves 19 residues There, ion pairs are broken when oxygen binds Glu Val causes sickle cell anemia! N
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A bowl of pasta is much more forgiving
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Many types of pasta can go into the same bowl of noodles
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Membrane components exchange neighbors easily individual components change shape dynamically neighbors held together non-covalently interactions with neighbors easily broken many interactions are fairly non-specific, driven by hydrophobic effect many different neighbors fit together
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Membrane components exchange neighbors easily
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Membrane components exchange neighbors easily
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Thus: membranes are both dynamic and stable many molecules move quite freely within the plane of the membrane speeds up to 1 µm/s = once around an E. coli in one second But: hydrophobic effect prevents components from leaving the plane of the membrane Hydrophobic effect leads to rapid resealing of broken edges
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A consequence: membranes are flexible A red blood cell stuck to a glass tube.
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BIO250 Spr11-25 - BIO250 BIO250 Introduction to...

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