Chapter 2 Part 1: Water, Weak Bonds and the Generation of Order Out of Chaos

Chapter 2 Part 1 Water, Weak Bonds, and the Generation of Order Out of Chaos  Learning Objectives Be able to name and describe how molecules move within solutions to allow them to interact. Be able to describe the features of water and understand how they make it a good...

Chapter 2 Part 1 Water, Weak Bonds, and the Generation of Order Out of Chaos  Learning Objectives Be able to name and describe how molecules move within solutions to allow them to interact. Be able to describe the features of water and understand how they make it a good solvent. Be able to list, describe, and identify the three types of noncovalent bonds.  2.1 Thermal Motions Power Biological Interactions Brownian motion – random fluctuation of energy content of the environment Random movement of molecules that can cause movement of typically non-motile particles Inside cells we find an aqueous environment Water allows Brownian motion to move molecules to allow for biochemical interactions  2.2 Biochemical Interactions Take Place in an Aqueous Water Solution Solvent – allows for things to dissolve in water Molecular formula – H2O Oxygen – electronegative atom (electron hog) Forms polar covalent bonds with hydrogen atoms Oxygen has a slightly negative charge Hydrogens have a slightly positive charge Electrons spend more time with oxygen Polar molecule – each side of the molecule has a different charge Different charges allow water molecules to interact with each other by hydrogen bonds Cohesive – water molecules attract to each other and other charged or polar molecules Makes it a good solvent  2.2 Biochemical Interactions Take Place in an Aqueous Solution Hydrophobic or Nonpolar Molecules Cannot dissolve in water Minimize interaction with water when mixed together Important in biological systems Form basis of membranes  2.3 Weak Interactions Are Important Biochemical Properties Readily reversible, noncovalent molecular interactions important for: DNA replication Protein folding Enzyme substrate interactions Molecular signaling Three types of noncovalent bonds 1. Ionic bonds (electrostatic interactions) 2. Hydrogen bonds 3. van der Waals interactions  2.3 Weak Interactions Are Important Biochemical Properties Ionic bonds Interactions between opposite electrical charges on atoms Strongest in nonpolar solvents Water weakens ionic bonds Charged portions on water interact with ions breaking the ionic bonds  2.3 Weak Interactions Are Important Biochemical Properties Hydrogen bond definition Textbook “A bond formed when two relatively electronegative atoms, such as oxygen or nitrogen, unequally share a hydrogen atom that is covalently bonded to one of the electronegative atoms.” Google “a weak bond between two molecules resulting from an electrostatic attraction between a proton in one molecule and an electronegative atom in the other.” Seely’s Anatomy and Physiology 12th edition “Hydrogen atoms bound covalently to either N or O atoms have a small positive charge that is weakly attracted to the small negative charge of other atoms, such as O or N; it can occur within a molecule or between different molecules.” Albert’s Molecular Biology of the Cell 4th edition “Noncovalent bond in which an electropositive hydrogen atom is partially shared by two electronegative atoms.”  2.3 Weak Interactions Are Important Biochemical Properties Hydrogen bonds Other molecules can have hydrogen bonds other than water Water weakens hydrogen bonds within other molecules by breaking those hydrogen bonds and forming new ones  2.3 Weak Interactions Are Important Biochemical Properties van der Waals Interactions Distribution of electric charge around an atom changes with time making parts of the atom partially charged and allows them to induce neighboring atoms to become partially charged so they can interact through electrostatic interactions. Interactions become interrupted when atoms are close together Electron clouds overlap and they repulse each other Weaker when single atoms interact Stronger when many atoms within a molecule become charged together