Lectures%20Jan%2029th%20and%20Feb%201st%20students

Lectures%20Jan%2029th%20and%20Feb%201st%20students - The...

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H14 6 D94 Proximal His The Bohr Effect Blue: OxyHb, R-State Grey: DeoxyHb, T-State HbR(O2)4 + nH+ <-------> HbT + 4O2 60% of the Bohr effect is due to the pH sensitive H146-D94 salt-bridge. To bind O2 , the F-helix moves toward the heme, breaking the salt-bridge. To release O2 , the F- helix moves away from the heme, forming the salt-bridge At lower pH, the salt-bridge is favored.
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H 2 C NH N H 2 C C O - O H 2 C NH + HN H 2 C C O - O I n c r e a si g p H Salt Bridges are pH Sensitive Salt Bridge pH 7.2 pH 7.6 The protonation state depends on pKa of both groups. At physiological pH, Histidine makes a great pH sensitive switch. Why? The Bohr salt-bridge is stable at pH 7.4, but His pKa is 6.0. Reason?
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H14 6 D94 Proximal His The Bohr Effect HbR(O2)4 + nH+ <-------> HbT + 4O2 Blue: OxyHb, R-State Grey: DeoxyHb, T-State Why is H146 protonated at pH of plasma (7.2)? What effect does lowering the pH have on the H194- D94 interaction and O2 release ? Which state of Hb would be favored if D94 was mutated to L?
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Hb changes during development Adult Hb α 2 β 2 Fetal Hb α γ 2 The γ subunit has less positive charges Significance? Enables transfer of O2 From adult to fetal blood across the placenta
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Sickle cell disease Polymerisation of haemoglobin in sickle cell patients causes cell shape changes, blockage of the peripheral circulation and can be lethal.
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Sickle Cell haemoglobin Glu6 to Val & - chain interaction aggregates Haemoglobin molecules. What type of interaction is it?
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Sickle cell selection Heterozygote Protected again Malaria Sickle cell Malaria
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Secondary Primary Tertiary Quaternary
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Protein Structure/Function Relationships Proteins carry out their wide range of functions because of: The large numbers of different shapes they can form Their ability to bind with each other and to other molecules Two broad categories Fibrous Globular
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Fibrous Proteins Have a structural function Have a low water solubility Large portions of individual protein molecules are in sheet or helical conformations Usually have a quaternary structure (2 or more protein molecules bond together) Are often mechanically strong
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Globular Proteins Far outnumber fibrous proteins Carry out wide range of functions within organisms Compact structures with high levels of tertiary structure giving highly specific shape for each protein Most polar residues to the outside of molecule making globular proteins relatively soluble Hydrophobic residues pack to the inside
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This note was uploaded on 02/19/2010 for the course BIOCHEMIST 34564 taught by Professor Gilbert during the Spring '10 term at UGA.

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Lectures%20Jan%2029th%20and%20Feb%201st%20students - The...

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