By: Debbie Schwagerman January 31, 2005

Atomic Bonds and Molecular Interactions Each atom has a defined number and geometry of covalent bonds. Each atom has a defined number and geometry of covalent bonds.

Atomic Bonds and Molecular Interactions Electrons are shared unequally in polar covalent bonds. Atoms with higher electronegativity values have a greater attraction for electrons.

Atomic Bonds and Molecular Interactions Covalent bonds are much stronger and more stable than noncovalent bonds.

Atomic Bonds and Molecular Interactions Ionic bonds result from the attraction of a positively charged ion (cation) for a negatively charged ion (anion). Ionic bonds result from the attraction of a positively charged ion (cation) for a negatively charged ion (anion). The atoms that form the bond have very different electronegativity values and the electron is completely transferred to the more electronegative atom. The atoms that form the bond have very different electronegativity values and the electron is completely transferred to the more electronegative atom. Ions in aqueous solutions are surrounded by water molecules, which interact via the end of the water dipole carrying the opposite charge of the ion. Ions in aqueous solutions are surrounded by water molecules, which interact via the end of the water dipole carrying the opposite charge of the ion.

Atomic Bonds and Molecular Interactions Van der waals interactions are caused by transient dipoles.

Atomic Bonds and Molecular Interactions The hydrophobic effect causes nonpolar molecules to adhere to one another.

Atomic Bonds and Molecular Interactions Molecular complementarity permits tight, highly specific binding of biomolecules.

Chemical Building Blocks of Cells Proteins Proteins Amino Acids Amino Acids Nucleic Acids Nucleic Acids Nucleotides Nucleotides Polysaccharides Polysaccharides Monosaccharide s Monosaccharide s

Chemical Building Blocks of Cells Common structure of amino acids.

Chemical Building Blocks of Cells 20 amino acids. 20 amino acids. All amino acids in nature are L form. All amino acids in nature are L form. Structure consists of C a, to which an amino group, a carboxyl group, a hydrogen atom, and a variable group. Structure consists of C a, to which an amino group, a carboxyl group, a hydrogen atom, and a variable group. Amino acids are classed according to their R group.

Chemical Building Blocks of Cells Common structure of nucleotides.

Chemical Building Blocks of Cells Common structure: phosphate group, base, and a five-carbon sugar. Common structure: phosphate group, base, and a five-carbon sugar. Sugar is either DNA or RNA. Sugar is either DNA or RNA. Bases are adenine, guanine, cytosine, thymine (DNA), and uracil (RNA). Bases are adenine, guanine, cytosine, thymine (DNA), and uracil (RNA). Nucleotides link together to build nucleic acids. Nucleotides link together to build nucleic acids.

Chemical Building Blocks of Cells Monosaccharides are carbohydrates of combinations of carbon and water in a one-to-one ratio. Monosaccharides are carbohydrates of combinations of carbon and water in a one-to-one ratio. Except for fructose, all sugars are in nature are D form. Except for fructose, all sugars are in nature are D form. D-Glucose (C 6 H 12 O 6 ) is primary energy source. D-Glucose (C 6 H 12 O 6 ) is primary energy source.

Chemical Building Blocks of Cells Polysaccharides: Polysaccharides: Disaccharides are simplest polysaccharides. Anomeric carbon of one sugar molecule is linked to hydroxyl oxygen of another sugar molecule. Polysaccharides can contain dozens to hundreds of monosaccharides.

Chemical Equilibrium The extent to which a reaction can proceed and the rate at which the reaction takes place determines which reactions occur in a cell. The extent to which a reaction can proceed and the rate at which the reaction takes place determines which reactions occur in a cell. Reactions in which the rates of the forward and backward reactions are equal, so that the concentrations of reactants and products stop changing, are said to be in chemical equilibrium. Reactions in which the rates of the forward and backward reactions are equal, so that the concentrations of reactants and products stop changing, are said to be in chemical equilibrium. At equilibrium, the ratio of products to reactants is a fixed value termed the equilibrium constant (K eq ) and is independent of reaction rate. At equilibrium, the ratio of products to reactants is a fixed value termed the equilibrium constant (K eq ) and is independent of reaction rate.

Chemical Equilibrium K eq depends on the nature of the reactants and products, the temperature, and the pressure. K eq depends on the nature of the reactants and products, the temperature, and the pressure. The K eq is always the same for a reaction, whether a catalyst is present or not. The K eq is always the same for a reaction, whether a catalyst is present or not. K eq equals the ratio of the forward and reverse rate constants (K eq = k f /k r ). K eq equals the ratio of the forward and reverse rate constants (K eq = k f /k r ). The concentrations of complexes can be estimated from equilibrium constants for binding reactions. The concentrations of complexes can be estimated from equilibrium constants for binding reactions.

Biochemical Energetics The change in free energy ∆G is the most useful measure for predicting the direction of chemical reactions in biological systems. Chemical reactions tend to proceed in the direction for which ∆G is negative. The change in free energy ∆G is the most useful measure for predicting the direction of chemical reactions in biological systems. Chemical reactions tend to proceed in the direction for which ∆G is negative. A chemical reaction having a positive ∆G can proceed if it is coupled with a reaction having a negative ∆G of larger magnitude. A chemical reaction having a positive ∆G can proceed if it is coupled with a reaction having a negative ∆G of larger magnitude. The chemical free energy change ∆G equals -2.3RT log keq. Thus the value of ∆G can be calculated from the experimentally determined concentrations of reactants and products at equilibrium. The chemical free energy change ∆G equals -2.3RT log keq. Thus the value of ∆G can be calculated from the experimentally determined concentrations of reactants and products at equilibrium.