tailieunhanh - Biochemistry, 4th Edition P19

Biochemistry, 4th Edition P19. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | What Are the Elements of Secondary Structure in Proteins and How Are They Formed 143 CRITICAL DEVELOPMENTS IN BIOCHEMISTRY In Bed with a Cold Pauling Stumbles onto the a-Helix and a Nobel Prize As high technology continues to transform the modern biochemical laboratory it is interesting to reflect on Linus Pauling s discovery of the a -helix. It involved only a piece of paper a pencil scissors and a sick Linus Pauling who had tired of reading detective novels. The story is told in the excellent book The Eighth Day of Creation by Horace Freeland Judson From the spring of 1948 through the spring of sputtered and blazed between Pauling s lab and Sir Lawrence Bragg s over protein. The prize was to propose and verify in nature a general three-dimensional structure for the polypeptide chain. Pauling was working up from the simpler structures of components. InJanuary 1948 he went to Oxford as a visiting professor for two terms to lecture on the chemical bond and on molecular structure and biological specificity. In Oxford it was April I believe I caught cold. I went to bed and read detective stories for a day and got bored and thought why don t I have a crack at that problem of alpha keratin. Confined and still fingering the polypeptide chain in his mind Pauling called for paper pencil and straightedge and attempted to reduce the problem to an almost Euclidean purity. I took a sheet of paper I still have this sheet of paper and drew rather roughly the way that I thought a polypeptide chain would look if it were spread out into a plane. The repetitious herringbone of the chain he could stretch across the paper as simply as this putting in lengths and bond angles from memory. .He knew that the peptide bond at the carbon-to-nitrogen link was always rigid b OHRH OHRH I I I I C 2 C N. C C .N C N C C N C C I I I I HRh oHRh oHR And this meant that the chain could turn corners only at the alpha carbons. creased the paper in parallel creases through the alpha .