Proteins

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  • Proteins are very important class of foof moleccules because they provide an organism not only with carbon and hydrogen, but with nitrogen and sulfur. 

Stereoisomers for Amino Acids

  • The carbon is attached to four diffrent groups in all amino acids except glycine 
  • Carbon of most amin acid is therefor chiral, allowing mirror image forms, enatiomers to exit
  • Glycine has two hydrogen atoms attached to the carbon and is the only amino acid commonly found in proteins that is not chiral 
  • The L-configuration of amino acids is isolated from proteins
  • The d notation is very similar to that discussed for carbonhydrates, but instead of the OH group we use the NH group to determine the D and which is L
  • Structures of amino acids at pH 70
  • General structure of an amino acid
  • Structures of the amino acid having hydrophobic, polar, neutral negativvely charged and positively charged R groups
  • The primary structure of a protein is the amino acid sequence of the protein chain 
  • Results from the covalent bonding between the amino acid residues in the chain. 

Secondary structure 

  • Repeating structures define the secondary structure of the protein 
  • Secondary structure is the result of hydrogen bondong between the amide hydrogens and carbonyl oxygens of the peptide bonds
  • Most common type of secondary structure is a coiled, helical conformation lnown as the helix. 
  • The helix has several important features

B pleated sheet 

  • Secondary common secondary structure in protein resembles the pleated fold of drapery and is known as B pleated sheets 
  • All of the carbonyl oxygens and amide hydrogens in a B pleated hseet are involved in hydrogen bonds, and the polypeptide chain is exxtended. 
  • Polypeptide chains in a b pleated sheet can have two orientations 
  • N termini are heat to head, structure is known as a parallel B pleated sheet
  • N terminus of one chain is aligned with the C terminus of a second chain, structure is known as an antiparallel B pleated sheet. 
  • The association of several polypeptides to produce a functional protein defines the quaternary structure of protein. 

Myoglobin and Hemoglobin 

  • To overcome solubility problem, we have

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