Pitt BIOSC 1000 - Secondary, Tertiary, and Quaternary Structure of Proteins (7 pages)

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Secondary, Tertiary, and Quaternary Structure of Proteins



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Secondary, Tertiary, and Quaternary Structure of Proteins

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This lecture explains the organized structure of proteins from the sequence of amino acids to the quaternary structure and function.


Lecture number:
4
Pages:
7
Type:
Lecture Note
School:
University of Pittsburgh
Course:
Biosc 1000 - Biochemistry

Unformatted text preview:

BIOSC 1000 Lecture 4 Outline of Last Lecture 1 Amino Acids 2 Peptides 3 Characteristics of Primary Structures of Proteins Outline of Current Lecture 1 2 3 4 5 6 Review of Peptides Properties of the Peptide Bond Secondary Structure of Proteins Tertiary Structure of Proteins Quaternary Structure of Proteins The Biological Protein Folding Problem Current Lecture 1 Review of Peptides Polypeptide backbone Amino acids can be joined to form polypeptides condensation reaction Polypeptides can be cleaved to yield monomers hydrolysis reaction Free amino acids are zwitterions near neutral pH Polypeptides have one N terminus and one C terminus and both termini will be charged near neutral pH unless chemically modified or blocked Polypeptide and protein sequences are written from N terminus to Cterminus WITHOUT EXCEPTION Peptide group contains 6 atoms Ca1 CO NH Ca2 Peptide group cannot be charged but forms H bonds o O and N are both electronegative o O acceptor N donor o Cis or trans peptide bonds Locate the two C bonding the peptide bones Trans Cs on opposite side of bonds no steric hindrance Cis steric clash Cs on same side of peptide bonds Trans predominates over cis conformation 2000 1 to avoid steric hindrance from bulky R groups clashing into each other Trans is only slightly favored when Xxx pro over cis 20 1 Peptide bond planarity means torsion angle is close to 180 degrees meaning usually trans or close to 0 degrees meaning rarely cis o 2 Properties of the Peptide Bond Example Proline To distinguish cis vs trans peptide conformation find both C next to one CO NH bond o If both C are on the same side cis o If C are on opposite sides trans and angles in the polypeptide backbone o C C N C amide bond or torsion angle omega o phi bond C N C C o psi bond N C C N When fully extended 180 Somewhat free rotation occurs about both and unlike Consequently 2 torsion angles define conformation of polypeptide backbone Certain and angle combinations are prohibited o Two torsion angles



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