Biochemistry 1 Recitation1 Cell & Water

Transcription

1 Biochemistry 1 Recitation1 Cell & Water

2 There are several important themes that transcends the chemistry and bring the importance of understanding the cell biological differences between eukaryotes and prokaryotes. These themes are all part of the evolution of eukaryotes. The evolution of internal membrane structures gives rise to the organelles referred to as the cytomembranes, while the other group belongs to the endosymbionts. How they arose and how the endosymbionts evolved has changed greatly since Lyn Margulis original thesis. What is the advantages of compartmentation? What drove the evolution of compartmentation?

3 Schematic diagram of an animal cell accompanied by electron micrographs of its organelles. The biochemistry of these organelles are universal. And in many ways similar if not identical to that of prokaryotes.

4 What is the advantage of density gradient centrifugation rather than differential cfg? CHRISTIAN DE DUVE Laboratory of Physiological Chemistry University of Louvain, Belgium and The Rockefeller Institute

5 The recent lipid rafts definition state that lipid rafts are very small ( nm), heterogeneous, highly dynamic, sterol- and sphingolipid- enriched domain [Pike, L., Rafts defined: a report on the Keystone Symposium on Lipid Rafts and Cell Function. The Journal of Lipid Research, (7): p ]. Therefore, we can indicate lipid rafts as saturated phospholipid and cholesterol-containing regions that depleted from the cholesterol-poor or unsaturated phospholipid regions. In the present, we have believed that lipid rafts involve many biological functions such as signaling, recruitment of specific proteins and endocytosis. With this point of view, biological membranes are not only cell barrier but also behave like a platform of biochemical reactions.

6 Structure of the water molecule. (a) The dipolar nature of the H 2 O molecule is shown in a ball-and-stick model; the dashed lines represent the nonbonding orbitals. There is a nearly tetrahedral arrangement of the outer-shell electron pairs around the oxygen atom; the two hydrogen atoms have localized partial positive charges (δ + ) and the oxygen atom has a partial negative charge (δ ). What is the dielectric constant? Although substance In a cell are aqueous, why is water problematic for reaction in a cell?

7 Strong dipole-dipole or charge-dipole interaction that arises between an acid (proton donor) and a base (proton acceptor) Typically 4 6 kj/mol for bonds with neutral atoms, and 6 10 kj/mol for bonds with one charged atom Typically involves two electronegative atoms (frequently nitrogen and oxygen) Hydrogen bonds are strongest when the bonded molecules are oriented to maximize electrostatic interaction Ideally the three atoms involved are in a line Structure of the water molecule. (b) Two H 2 O molecules joined by a hydrogen bond (designated here, and throughout this book, by three blue lines) between the oxygen atom of the upper molecule and a hydrogen atom of the lower one. Hydrogen bonds are longer and weaker than covalent O H bonds.

8 H 2 O <-> H + + OH - O-H bonds are polar and can dissociate heterolytically Products are a proton (H + ) and a hydroxide ion (OH ) Dissociation of water is a rapid reversible process Most water molecules remain un-ionized, thus pure water has very low electrical conductivity (resistance: 18 M cm) The equilibrium is strongly to the left Extent of dissociation depends on the temperature

9 Proton hopping. Short hops of protons between a series of hydrogen-bonded water molecules result in an extremely rapid net movement of a proton over a long distance. As a hydronium ion (upper left) gives up a proton, a water molecule some distance away (lower right) acquires one, becoming a hydronium ion. Proton hopping is much faster than true diffusion and explains the remarkably high ionic mobility of H + ions compared with other monovalent cations such as Na + and K +.