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Lecture 6

MBIO 2360 Lecture 6: Lecture 6 – MBIO
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Department
Microbiology
Course
MBIO 2360
Professor
Mc Kenna Sean
Semester
Fall

Description
Lecture 6 – MBIO/CHEM 2360 Protein Structure  Proteins are polymers of amino acids o i.e. Polyaminoacid or Polypeptides  Peptide bond is the name given to the amide bond that joins two amino acids o Formed by condensation o Draw example o Ribosome makes peptide bonds  Proteins are linear molecules of amino acids joined by amide (peptide) bonds formed by simple removal of H2O from: equation  Repeating backbone is non-ionizable, except at the ends o The H's on the N beside the carbonyl must be on the opposite side of the O o Draw example  Side chains vary depending on amino acid  pKa, pI of side chains and termini are similar to free AA  When peptide bonds are formed, alpha-NH3 and alpha-COO groups become covalently linked and can no longer ionize in solution  Charged groups of polypeptides are limited to the two ends (termini) and some of the R groups  Amino acid units in a peptide or protein are called residues  The amino acid sequence of peptides and proteins is always written with the N-terminal residue on the left, and the C-terminal residue on the right: o Example  Polypeptide chains are very flexible, so they way they fold up to form a compact, 3D structure is an essential aspect of protein structure o Peptide bond is not flexible  Folding a protein is believed to be determined by it’s AA sequence o We cannot predict this yet, but we have many protein structures (determined by X-ray crystallography, or sometimes NMR) and the basic principles of protein folding are understood  To describe the structure of protein completely, four levels of structural information must be specified The Four Levels of Protein Structure 1. Primary structure - linear sequence of amino acid residues 2. Secondary structure - regular conformational patterns of contiguous portions of the polypeptide chain, stabilized by hydrogen bonds 3. Tertiary structure - overall fold of the entire polypeptide chain to give a globular 3D structure 4. Quaternary structure - the interaction of two or more globular polypeptides to form a multisubunit protein Primary Structure  The sequence or order of amino acids in the protein is the primary structure  The first protein sequence was determined in the 1950s by Fred Sanger (Nobel Prize 1958)  This success was followed by the direct sequencing of thousands of proteins  Sanger then developed a method for DNA sequencing (Nobel Prize 1980), now automated  Most protein sequences today are determined from the DNA sequence of the
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