Chapter 5 Chem 341 Suroviec Fall 2013. I. Introduction Every protein has a unique 3-D structure.
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Transcript of Chapter 5 Chem 341 Suroviec Fall 2013. I. Introduction Every protein has a unique 3-D structure.
![Page 1: Chapter 5 Chem 341 Suroviec Fall 2013. I. Introduction Every protein has a unique 3-D structure.](https://reader030.fdocuments.in/reader030/viewer/2022032702/56649ceb5503460f949b600c/html5/thumbnails/1.jpg)
Chapter 5
Chem 341
Suroviec Fall 2013
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I. Introduction
• Every protein has a unique 3-D structure
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II. Myoglobin
• Small intercellular protein
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A. Heme group
• Heme contains 4 pyrrole groups• Fe(II) atom at the center is coordinated
by the 4 porphyrin N atoms and one N from a His side chain
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B. Equilibrium of O2 binding
• Myoglobin binding of O2 is simple equilibrium
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C. Binding Curve
Steepness of hyperbola increases as K decreases
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III. Hemoglobin Structure & Mechanism
• 4 polypeptide chains– 2 subunits– 2 subunits
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III. Hemoglobin Structure & Mechanism
• Oxygenation causes extensive quaternary structural changes
• Oxy- and Deoxy- Hb have different forms
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A. Binding of O2
• T-state (deoxy)
• R-state (oxy)
In T state (blue) Fe(II) located 0.6 Å out of heme plane
When O2 binds Fe-N porphyrin bonds contract and Fe(II) moves in plane (red)
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B. 2 Stable Positions
• Difference between T and R occur at 1-2 and 2-1 interface
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C. Role of Globin in Binding of O2
• Protect Fe(II)
• His attached to backside of porphyrin
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D. Relative Stability of T and R
• With no O2 present: T more stable
• With O2 present: R more stable
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V. Hemoglobin binding and pH
• Effect of pH on Hb transport
• Lung pH = 7.6
• Blood pH = 7.2
• pO2 in tissues = 30 torr
• pO2 in lungs = 95 torr
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Bohr Effect
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VI. 2 – 3 Bis-phosphoglycerate
• Red blood cells use BPG to fine tune hemoglobin function
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VII. Abnormal Hemoglobins• Sickle Cell Anemia
– Deoxyhemoglobin S forms insoluble filaments that deform red blood cells
– Rigid sickle shaped cells cannot pass through the capillaries
– Results in tissue death: lack of oxygen
– Mutant hemoglobin where hemoglobin S contains Val instead of Glu at the 6th position of the chain
– Causes polymerization of hemoglobins
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VIII. Structural Proteins
Typical eukaryotic cells have 3 types of cytoskeletal proteins that form fibers
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A. Microfilaments
• Made of actin
• Network of microfilaments support plasma membrane
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B. Microfilaments extend/retract
• Polymerization of actin monomers is reversible process so the polymer undergoes constant shrinking and growing as subunits add to and dissociate from one or both ends of the microfilaments
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C. Microtubules
• Microtubules are cytoskeletal fibers built from globular protein subunits
• Microtubules can assemble and disassemble on a time scale that allow the cell to rapidly change shape in response to external or internal stimuli
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D. -Keratin
• Intermediate filaments are structural proteins• Chemically un-reactive• Component of hair, horns, nails and feathers -helix shape, but exhibits smaller than
expected spacing - due to coiled coil structure
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E. Collagen
• Most abundant animal protein• Major stress-bearing components of connective tissues (bone, teeth, tendons)• Has distinct amino acid composition
– Every 3rd amino acid = glycine
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E. Collagen
• Cross-linking between fibrils also increases insolubility• Can’t be S-S bonds• Cross-link between Lys and His chains using Lysyl oxidase• Tends to occur near termini