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| O2 binding: changes hemoglobin structure |
-dimer rearrangement at interface
-communication between subunits enables cooperativity
-beta chain movement!
-T->R shift allows the binding of O2 to increase the binding affinity at the other sites! |
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lhittson Sun, 04 Nov 2007 23:11:40 GMT |
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| Oxyhemoglobin |
-R State
-1 pair of alpha/beta subunits rotates 15 degrees with respect to the other upon O2 binding
-favors binding of substrate |
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lhittson Sun, 04 Nov 2007 22:54:10 GMT |
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| Deoxyhemoglobin |
-T state
-heme groups are well separated
-favors non-binding of the substrate |
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lhittson Sun, 04 Nov 2007 22:54:34 GMT |
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| Hemoglobin cooperativity |
-allows delivery of 1.7X more O2 than it would if the sites were independent
-66% drop in saturation (38% if independent, 7% for myoglobin) |
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lhittson Sun, 04 Nov 2007 22:53:19 GMT |
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| PO2 lungs |
100 torr |
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lhittson Sun, 04 Nov 2007 22:53:19 GMT |
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| PO2 Tissues |
20 torr |
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lhittson Sun, 04 Nov 2007 22:53:19 GMT |
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| Allosteric Enzymes |
-ADJUST TO MEET THE IMMEDIATE NEEDS OF THE CELL, KEY REGULATOR OF METABOLIC PATHWAYS
-multiple active sites
-sigmoid kinetics
-can have cooperative binding
-regulatory molecules bind to sites other than the active site |
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lhittson Sun, 04 Nov 2007 22:47:04 GMT |
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| Hemoglobin O2 binding |
-COOPERATIVE, sigmoid binding, S shaped, lag before binding occurs
-P50 = 26 torr |
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lhittson Sun, 04 Nov 2007 22:47:04 GMT |
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| Myoglobin O2 binding |
-non-cooperative (simple chemical equilibrium)
-P50 = 2 torr |
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lhittson Sun, 04 Nov 2007 22:47:04 GMT |
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| Reactive Oxygen Species |
-myoglobin's structure inhibits their release
-resonance structures distribute electrons between oxygen and iron
-2nd His in O2 binding pocket, donates H bond to O2 --> O2's superoxide ion hcaracter strengthens the bond |
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lhittson Sun, 04 Nov 2007 22:47:04 GMT |
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| Structural changes at iron sites in myoglobin and hemoglobin |
1) Fe2+ binds to 4 pyrrole nitrogen atoms at Heme center
2) 5th coordination site: Fe2+ binds to the imidazole ring of proximal His
3) 6th coordination site: Fe2+ binds O2, changes electronic structure, allows Fe2+ to sit within the plane of the porphyrin in heme
-changes magnetic properties, can take advantage of the magnetic properties of the brain and use fMRI! study brain function |
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lhittson Sun, 04 Nov 2007 22:38:56 GMT |
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| What state is iron in myoglobin/hemoglobin? |
-Ferrous: Fe2+ |
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lhittson Sun, 04 Nov 2007 22:38:56 GMT |
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| Heme |
-gives red color of blood and muscle
-allows O2 to bind |
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lhittson Sun, 04 Nov 2007 22:38:56 GMT |
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| Hemoglobin: what is it? function? |
-protein in RBCs
-Tetramer: 2alpha, 2beta chains
-carries oxygen from lungs to tissues
-transports CO2 and H+ from tissues to lungs
-chains bind O2 COOPERATIVELY |
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lhittson Sun, 04 Nov 2007 22:38:56 GMT |
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| Myoglobin: what is it? function? |
-a protein expressed in muscle cells
-SINGLE polypeptide chain = MONOMER
-reservoir supply of oxygen when needed |
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lhittson Sun, 04 Nov 2007 22:29:53 GMT |
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| How do cells get adequate oxygen? |
1. Circulatory System
2. Oxygen binding proteins
-Myoglobin: oxygen storage (MUSCLE)
-Hemoglobin: oxygen transport |
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lhittson Sun, 04 Nov 2007 22:29:53 GMT |
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| How much more energy can our cells extract from glucose with oxygen compared to without oxygen? |
In the presence of O2, cells can extract 15X more energy from glucose than when oxygen is absent |
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lhittson Sun, 04 Nov 2007 22:29:53 GMT |
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| Regulatory Strategies for Enzymes |
A. Allosteric: distinct regulatory sites
B. Multiple forms of an enzyme
C. Reversible covalent modification
D. Proteolytic cleavage
E. Controlling the amount of enzyme present |
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lhittson Sun, 04 Nov 2007 22:29:53 GMT |
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