Study Biochemistry Lecture Chapters 7&10 Flash Cards

 
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Biochemistry Lecture Chapters 7&10

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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!
Deoxyhemoglobin
-T state
-heme groups are well separated
-favors non-binding of the substrate
Oxyhemoglobin
-R State
-1 pair of alpha/beta subunits rotates 15 degrees with respect to the other upon O2 binding
-favors binding of substrate
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)
PO2 lungs
100 torr
PO2 Tissues
20 torr
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
Hemoglobin O2 binding
-COOPERATIVE, sigmoid binding, S shaped, lag before binding occurs
-P50 = 26 torr
Myoglobin O2 binding
-non-cooperative (simple chemical equilibrium)
-P50 = 2 torr
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
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
What state is iron in myoglobin/hemoglobin?
-Ferrous: Fe2+
Heme
-gives red color of blood and muscle
-allows O2 to bind
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
Myoglobin: what is it? function?
-a protein expressed in muscle cells
-SINGLE polypeptide chain = MONOMER
-reservoir supply of oxygen when needed
How do cells get adequate oxygen?
1. Circulatory System
2. Oxygen binding proteins
-Myoglobin: oxygen storage (MUSCLE)
-Hemoglobin: oxygen transport
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
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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