5-notes - 580.221 BME Molecules and Cells L05 Binding;...

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580.221 BME Molecules and Cells L05 Binding; Hemoglobin p 1 Lecture Five – Protein Structure 2 & Binding: Hemoglobin Outline: Structure determines function Coordination; Heme Binding valence Cooperativity; Hill equation I. Review of Fractional Occupancy Semipermeable membrane (dialysis) approach: - Receptors on only 1 side, can’t pass membrane - Free ligands equilibrate across membrane - Detect total ligands on each side of membrane Additional ligands on side with receptors are the bound fraction. Example of this? Red blood cells apply this tactic – by using hemoglobin to bind oxygen, the red blood cells carry many times more oxygen than they could carry simply dissolved in blood. The oxygen diffuses across the cell membrane but the Hb cannot. Derivation of Fractional Occupancy: (R = receptor, L = ligand) for a univalent receptor-ligand interaction [] [] [] RL L R K d = so [] [][ ] d K L R RL = [] [ ] [ ] RL R R total + = so [] [ ] [ ][ ] d total K L R R R + = [] [] [] [] [] [] [] [] [] L K L K L R R K L R R RL d d d total + = + = = θ II. Key Vocabulary Myoglobin (Mb)– binds 1 O 2 , holds oxygen in tissue Hemoglobin (Hb)– binds 4 O 2 , looks like 4 myoglobins, transports oxygen in red blood cells from lungs to tissues. Heme – prosthetic group for Myoglobin or Hemoglobin that binds O 2 , consists of porphyrin ring and Fe 2+ Cooperativity - binding to one site affects binding to other sites on same molecule Hill Coefficient – describes degree of cooperativity Residue / Side Chain – the moiety on an amino acid that isn’t the backbone of a polypeptide Conformational Change – protein shape change, often
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580.221 BME Molecules and Cells L05 Binding; Hemoglobin p 2 Cofactor/prosthetic group – additional molecule required for enzymatic activity. Sigmoidal – “S” shaped θ = fractional saturation (occupation) III. Structure determines function; why? Weak bonds. Immunoglobulin domain
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5-notes - 580.221 BME Molecules and Cells L05 Binding;...

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