{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

CHAPTER 4 (Figures) - David L Nelson and Michael M Cox...

Info icon This preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
Lehninger Principles of Biochemistry Fourth Edition Chapter 4: The Three-Dimensional Structure of Proteins Copyright  ©  2004 by W. H. Freeman & Company David L. Nelson and Michael M. Cox
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
2 Protein Secondary Structure Secondary structure refers to local conformation of some part of the peptide. These structures include 1. α -helix 2. β -sheets and 3. β -turns
Image of page 2
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
4 Protein Secondary Structure i. The α -helix This is the most common protein secondary structure. The simplest arrangement the polypeptide chain assumes with its rigid bonds a helical structure, which Pauling and Corey called the α -helix ( Fig. 4-4 ). In this structure, the polypeptide backbone is tightly would around an imaginary axis drawn longitudinally through the middle of the helix, and the R groups of amino acid residues protrude outward from the helical backbone. Repeating unit is a single turn of the helix, which extend about 5.4 Å along the axis. The amino acid residues in an α -helix have conformation with ϕ = -45º to –50º and φ = -60º, and each helical turn include 3.6 amino acid residues . The helical twist of the α -helix found in all proteins is right- handed .
Image of page 4
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
6 Protein Secondary Structure Why does α -helix form more rapidly than the other? Because α -helix make the optimal use of the internal H-bonds. How? The structure is stabilized by H-bonds between H atom attached to the electronegative N atom of the linkage and the electronegative carbonyl oxygen atom of the fourth amino acid on the N-terminal side of the peptide bond ( Fig. 4- 4b ) Each successive turn of α -helix is held to adjacent turns of three to four H- bonds . All the H-bonds combined give the entire helical structure considerable stability. Amino acid sequence vs α -helix stability a). The electrostatic repulsion (or attraction) between successive amino residues with charged groups. Example ; Long chain of Glu residues will disrupt α -helix structure at pH 7.0 because the – vely charged carboxyl group of the adjacent glu residues repel each other and so strongly that they overcome the stabilizing influence of H-bonds on the α -helix. b). The bulkiness of the adjacent R groups. Example ; The bulk and shape of Asn, Ser, Thr and Cys residues can destabilize an α -helix if they are close together in the chain.
Image of page 6
7 Protein Secondary Structure Amino acid sequence vs α -helix stability (cont) c). The interactions between amino acid side chains spaced three (or four) residue apart. Example ; Positively charged amino acids are after found three residues away from negatively charged amino acids, permitting the formation of an ion-pair. Two aromatic acid residues are often similarly spaced resulting in a hydrophobic interaction.
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern