Standard II Objective 1 C & D

Objective 1 C. Explain how the properties of water (e.g. cohesion, adhesion, heat capacity, solvent properties) contribute to the maintenance of cells and living organisms.

Polarity of Water Molecules that have an unequal distribution of charges are polar molecules (partial positive and partial negative electrical charges). A weak interaction involving a hydrogen atom and a fluorine, oxygen or nitrogen is called a hydrogen bond. Hydrogen bonding is a strong type of van der Walls force.

Visualizing properties of water

Visualizing properties of water continued

Capillary Action Capillary or wicking is the ability of a liquid to flow in narrow spaces without the assistance of, and in opposition to, external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper, in some non-porous materials such as liquefied carbon fiber, or in a cell. It occurs because of intermolecular forces between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container act to lift the liquid. http://hyperphysics.phy-astr.gsu.edu/%e2%80%8chbase/Fluids/imgflu/capi.gif

Heat Capacity Water has a very high specific heat capacity – the second highest among all the heteroatomic species (after ammonia), as well as a high heat of vaporization (40.65 kJ/mol or 2257 kJ/kg at the normal boiling point), both of which are a result of the extensive hydrogen bonding between its molecules. These two unusual properties allow water to moderate Earth's climate by buffering large fluctuations in temperature. http://ga.water.usgs.gov/edu/pictures/heat-capacity-pond.gif

Solvent Properties A mixture is a combination of two or more substances. Homogeneous mixtures – when a mixture has a uniform composition also called a solution. Solvent – a substance in which another substance is dissolved. Solute – the substance that is dissolved into the solvent Heterogeneous mixtures – a mixture where the components remain distinct.

Water is a universal solvent Water is called the universal solvent because more substances dissolve in water than in any other chemical. This has to do with the polarity of each water molecule. The hydrogen side of each water (H2O) molecule carries a slight positive electric charge, while the oxygen side carries a slight negative electric charge. This helps water dissociate ionic compounds into their positive and negative ions. The positive part of an ionic compound is attracted to the oxygen side of water while the negative portion of the compound is attracted to the hydrogen side of water. Despite its name as the "universal solvent" there are many compounds water won't dissolve or won't dissolve well. If the attraction is high between the opposite-charged ions in a compound, then the solubility will be low. Nonpolar molecules don't dissolve very well in water, including many organic compounds, such as fats and waxes.

Solvent properties continued

pH scale Acids – substances that release hydrogen ions (H+) The more acidic the substance the more hydrogen ions are released Bases – substances that release hydroxide ions (OH-) The more basic the substance the more hydroxide ions are released pH – the measure of the concentration of H+ ions in a solution Acids are lower than pH7 and bases are higher than pH 7 Buffers are mixtures that react with acids or bases to keep the pH is a certain range. Buffers keep cells in the pH range of 6.5 – 7.5 Blood has a pH of about 7.4

pH scale continued

Assesment Describe one way in which water helps maintain homeostasis. How does the structure of water allow it to act as a solvent? Explain why the following molecules are acidic, basic, or neutral: water H20, hydrochloric acid HCl, and sodium hydroxide NaOH Give one example of a solution and a suspension. If you add HCl to water, what effect would this have on the H+ concentration? On the pH?

Take Away The polarity of water allows for unique properties that are necessary for life. Water forms hydrogen bonds Properties Adhesion/cohesion – capillary action Water is the universal solvent High heat capacity

Honors Curriculum Emphasize polarity and hydrogen bonds. A solid understanding of the properties of water is essential to prepare for upper level courses. pH scale (possible applications: water, enzyme function, and acid rain)

Objective 1 D. Explain the role of enzymes in cell chemistry.

The law The law of conservation of mass - mass can neither be created nor destroyed

Reactants and products A chemical reaction is the process by which a group of atoms or groups of atoms are reorganized into different substances 8Fe + 6O2  4Fe2O3

Chemical equations When we write chemical reactions, we express each component of the reaction in a chemical equation. The reactants (starting substances) are shown on the left side of the equation The products are the substances formed and are shown on the right side of the equation.

Skill practice – balance the following equations K + B2O3  K2O + B HCl + NaOH  NaCl +H2O CH4 + O2  CO2 + H2O N2 + H2  NH3 Al + S8  Al2S3

Explain why the number of atoms of reactants must equal the number of atoms in products formed.

Activation energy The minimum amount of energy needed for the reactants to form products is the activation energy Exothermic reactions release energy Endothermic reactions absorb heat

Enzymes are Proteins Catalysts are substances that lower the activation energy needed to start a chemical reaction Enzymes are the biological catalysts that speed up the rate of chemical reactions in biological processes.

Induced fit model The reactants that bind to the enzyme are called substrates. The specific location where a substrate binds on an enzyme is called the active site.

Competitive/noncompetitive inhibitors Enzyme function and inhibition During the normal enzyme catalytic cycle the substrate encounters an enzyme with the specific active site to which it binds forming an enzyme substrate complex. The enzyme then facilitates the breakdown at the substrate to its products which part from the enzyme leaving the active site free to catalyze another substrate as the cycle begins again. Competitive inhibition occurs when an enzyme encounters a blocker which mimics the properties at the substrate and binds the enzyme's active site, thus when the substrate is encountered the active site is not available for attachment and no reaction will occur. Non-competitive enzyme inhibition involves the binding a blocker to the enzyme away from the active site this binding causes a conformational change in the enzyme altering the shape of the active site which prevents a substrate from binding no reaction will occur as long as a non-competitive blocker is bound to the enzyme.

Describe the importance of enzymes to living organisms.

pH and enzyme function

Temperature and enzyme function

Salt and enzyme function Salts and ions may have many different effects of the activity of an enzyme. For example, ions may bind to a charged side chain of a protein. This kind of interaction, although not changing the tertiary structure of the enzyme in a substantial manner could make it easier for a substrate molecule to locate or bind to the active site of the enzyme. Thus the presence of the ion in optimum concentrations could alter the rate of the reaction.

Assessment Identify the parts of this chemical reaction: A + B  AB Diagram the energy changes can take place in a chemical reaction. Label the reactants and products the balance the equation. ___ H2O2  ___ H2O + O2

Take away Enzymes are proteins Enzymes can change the rate of biological reactions

Honors curriculum Induced fit model Competitive/noncompetitive inhibitors Effects of changes in pH, temperature, and salt on enzyme function