Coupling of Phosphorylation to Electron and Hydrogen Transfer by a Chemi-Osmotic type of Mechanism

Publisher Summary This chapter reviews that the simplest way of accounting for the absorption spectrum of a protein is as the sum of the spectra of its components. This gives results which are often good approximations to the observed protein spectrum. The assumption of additivity is basic for useful analytical applications of spectral measurements. It discusses that in another perspective, the failure of perfect additivity of the component absorptivities affords the possibility of obtaining structural information about proteins. The absorptivity of the peptide bond can change by as much as a factor of two with a change in the conformation of a peptide chain. Since the absorptivity of aromatic side chains is much less sensitive to environmental change, correspondingly, more sensitive techniques are required to measure the small changes which do occur. The nature and limitations of the structural information resulting from both peptide-bond and side-chain absorption are discussed. Absorption spectra can occasionally be a useful tool in the identification of unusual structural features in proteins and polypeptides. Several such applications are also explained in this chapter.

Ultraviolet spectra Of Proteins and Amino Acids

http://www.chem.ualberta.ca/~campbell/resources/Bioanalytical-2012/Ribosome_Steitz_short.pdf

RNA, the first macromolecular catalyst: the ribosome is a ribozyme

The assumption of locally additive forces is used to describe the London—van der Waals dispersion attraction between long saturated chains. For two linear chains of length L, opposed and parallel, each built out of N identical units of length λ(Nλ=L), the total dispersion energy is given by W=A4λ2D4ρ(3tan−1ρ+ρ1+ρ2),  ρ=LD, where D is the mutual distance of the two chains; A is the coefficient of the dispersion interaction between two basic units. At distances D much smaller than the molecular length L, the energy becomes proportional to L (or N) and inversely proportional to the fifth power of the intermolecular distance.The coefficient A is calculated for the interaction between two CH2 units in hydrocarbon chains and the result is used to estimate the sublimation energy at 0°K of paraffin crystals. Sound agreement with experiment is obtained. Finally, the particularities of the attractive forces between long saturated chains are examined in more detail and their great sensitivity to distance is shown by...

Attractive Forces between Long Saturated Chains at Short Distances

Cytoskeletal proteins tagged with green fluorescent protein were used to directly visualize the mechanical role of the cytoskeleton in determining cell shape. Rat embryo (REF 52) fibroblasts were deformed using glass needles either uncoated for purely physical manipulations, or coated with laminin to induce attachment to the cell surface. Cells responded to uncoated probes in accordance with a three-layer model in which a highly elastic nucleus is surrounded by cytoplasmic microtubules that behave as a jelly-like viscoelastic fluid. The third, outermost cortical layer is an elastic shell under sustained tension. Adhesive, laminin-coated needles caused focal recruitment of actin filaments to the contacted surface region and increased the cortical layer stiffness. This direct visualization of actin recruitment confirms a widely postulated model for mechanical connections between extracellular matrix proteins and the actin cytoskeleton. Cells tethered to laminin-treated needles strongly resisted elongation by actively contracting. Whether using uncoated probes to apply simple deformations or laminin-coated probes to induce surface-to-cytoskeleton interaction we observed that experimentally applied forces produced exclusively local responses by both the actin and microtubule cytoskeleton. This local accomodation and dissipation of force is inconsistent with the proposal that cellular tensegrity determines cell shape.

https://rupress.org/jcb/article-pdf/145/1/109/1284421/9810083.pdf

D. E. Goldman

Papers

Biophysical Science-A Study Program