amino acid & protein 2012

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Biochemistry
Second Year

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amino acid & protein 2012

  1. 1. AMINO ACID & PROTEIN
  2. 2. Peptide bond → Dipeptide & Polypeptide: Two amino acids are linked together with the elimination of H2O (i.e. dehydration). This reaction (polymerization) is catalyzed by enzymes (i.e. specific) where an amide bond is formed between the α-carboxyl group of one amino acid and the α-amino group of the other amino acid. This amide bond is called peptide bond , and it gives us a dipeptide.
  3. 3. A third amino acid is added to the carboxylic end of a dipeptide to form a tripeptide, and so on… to form polypeptide or a protein. By convention the amino end (called N- terminal) is written at the beginning of the polypeptide chain (with R#1), and therefore the carboxy terminal (C-terminal) is the end of the chain (with R#n). This chain is unbranched and has one direction.
  4. 4. Hb Structure: Globin consists of 4 polypeptide chains in tetrahedral array ( 4° structure ) . 2 α- chains + 2 β- chain 1°141a’ a’ 146 a’ a’ Normally, as in Hb A Each chain 2°#of α-helices # of α-helices seven eight 3°spheroidal spheroidal with heme inside, with heme inside, where iron connected to where iron connected to one a’a’(proximal histidine) one a’a’(proximal histidine(
  5. 5. Looking at heme 1.In deoxy-Hb Fe is 0.4 A° out of heme plane towards proximal histidine in globin. 2. Upon oxygenation to oxy-Hb Fe moves into the plane of porphyrin (heme) pulling with it the proximal histidine (in globin). 3. Movement is transmitted to interfaces between subunits, and T R loosing salt bridges. Cooperativity can be explained by the fact that the #of salt bridges to be broken by 1st O2 added are more than 2nd O2 > 3rd O2 > 4th O2.
  6. 6. Looking at heme 1.In deoxy-Hb Fe is 0.4 A° out of heme plane towards proximal histidine in globin. 2. Upon oxygenation to oxy-Hb Fe moves into the plane of porphyrin (heme) pulling with it the proximal histidine (in globin). 3. Movement is transmitted to interfaces between subunits, and T R loosing salt bridges. Cooperativity can be explained by the fact that the #of salt bridges to be broken by 1st O2 added are more than 2nd O2 > 3rd O2 > 4th O2.

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