CHAPTER 2 CHEMISTRY OF LIFE

2-1 The Nature of Matter

 Atom – the basic unit of matter  Atoms are extremely small. 100 million atoms placed side by side would be about the width of your pinkie.  Atoms contain subatomic particles that are even smaller. These include protons, neutrons, and electrons.

 Protons and neutrons have the same mass. Protons are positively charged particles and neutrons have no charge (neutral)  Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom.

 Electron – a negatively charged particle. It is much smaller than the proton.  Atoms have an equal number of protons and electrons  Subatomic particles have equal but opposite charges, so atoms are neutral.

 Element – a pure substance that consists entirely of one type of atom.  More than 100 elements are known, but only about two dozen are commonly found in living organisms.  Elements are represented by a one or two letter symbol.

 Isotopes – atoms of the same element that differ in the number of neutrons they contain  Ex – some atoms of carbon have 6 neutrons, some have 7, and some have 8  Because they have the same number of electrons, all isotopes of an element have the same chemical properties.

Chemical Compounds  Chemical compound – a substance formed by the chemical combination of two or more elements in definite proportions.  Ex. Water = H 2 O Salt = NaCl  The physical and chemical properties of a compound are usually very different from those of the elements from which it is formed.

Chemical Bonds  The atoms in compounds are held together by chemical bonds.  The main types of chemical bonds are ionic bonds and covalent bonds.

Ionic Bond – formed when one or more electrons are transferred from one atom to another

Covalent Bond – forms when electrons are shared between atoms

 Molecule – the smallest unit of most compounds  Van der Waals Forces – a slight attraction that develops between the oppositely charged regions of nearby molecules  Van der Waals forces are not as strong as ionic bonds or covalent bonds but can hold molecules together, especially when the molecules are large.

 Ex – gecko foot  A gecko can climb up walls. Their foot is covered by as many as half a million tiny hairlike projections. Each projection is further divided into hundreds of tiny, flat- surfaced fibers. This allows the gecko’s foot to come in contact with an extremely large area of the wall at the molecular level. Van der Waals forces form between molecules on the surface of the gecko’s foot and molecules on the surface of the wall. The combined strength of all the van der Waals forces allows the gecko to balance the pull of gravity.

2-2 Properties of Water

The Water Molecule  A polar molecule is a molecule in which the charges are unevenly distributed.  A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms.  The negative pole is near the oxygen atom and the positive pole is between the hydrogen atoms

 Cohesion – an attraction between molecules of the same substance.  Water is extremely cohesive.  Cohesion explains why some insects can walk on a pond’s surface.

 Adhesion – an attraction between molecules of different substances.  Ex – water in a graduated cylinder adheres to the sides, causing the sides of water to be higher than the center

 Mixture – a material made up of two or more elements or compounds that are physically mixed together but not chemically combined.  Ex – salt and pepper mixed together

 Solution – mixture of two or more substances in which the molecules of the substances are evenly distributed  Solute – the substance that is dissolved  Solvent – the substance in which the solute dissolves  Ex – mixing salt into water is a solution. Salt is the solute, water is the solvent  Suspension – mixture of water and non-dissolved materials

Acids, Bases, and pH  pH Scale – indicates the concentration of H + ions in solution  The pH scale ranges from 0 – 14. A pH of 7 is neutral. Below 7 is acidic, above 7 is more basic.  Acid – any compound that forms H + ions in a solution. Acidic solutions contain higher concentrations of H + ions than pure water and have pH values below 7.  Base – a compound that produces hydroxide ions (OH - ions) in solution. Basic (alkaline) solutions contain lower concentrations of H + ions than pure water and have pH values above 7.  Buffers – weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH.

2-3 Carbon Compounds

Four groups of organic compounds found in living things are carbohydrates, lipids, nucleic acids, and proteins

 Carbohydrates – compounds made up of carbon, hydrogen, and oxygen atoms, usually in a ratio of 1:2:1  Living things use carbohydrates as their main source of energy. Plants and some animals also use carbohydrates for structural purposes.

 Lipids – a large and varied group of biological molecules that are generally not soluble in water. They are made mostly from carbon and hydrogen atoms. Some lipids are fats, oils, and waxes.  Lipids can be used to store energy. Some lipids are important parts of biological membranes and waterproof coverings.

Nucleic Acids – macromolecules containing hydrogen, oxygen, nitrogen, carbon, and phosphorus. They are formed from nucleotides.

 Nucleotides – consist of three parts: a 5-carbon sugar, a phosphate group, and an nitrogenous base  Nucleic acids store and transmit genetic information.  Two types of nucleic acids are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA)

 Proteins – macromolecules that contain nitrogen as well as carbon, hydrogen, and oxygen.  Proteins are polymers of amino acids. Amino acids are compounds with an amino group (-NH 2 ) on one end and a carboxyl group (-COOH) on the other end.  Some proteins control the rate of reactions and regulate cell processes. Some are used to form bones and muscles. Others transport substances into or out of cells or help to fight disease.

2-4 Chemical Reactions and Enzymes

 Chemical Reaction – a process that changes one set of chemicals into another set of chemicals.  Reactants – the elements or compounds that enter into a chemical reaction  Products – the elements or compounds produced by a chemical reaction  Chemical reactions always involve the breaking of bonds in reactants and the formation of new bonds in products.

Energy in Reactions  Chemical reactions that release energy often occur spontaneously. Chemical reactions that absorb energy will not occur without a source of energy.  Ex – hydrogen gas burning with oxygen to produce water vapor

 Activation Energy – the energy that is needed to get a reaction started  Catalyst – a substance that speeds up the rate of a chemical reaction. Catalysts work by lowering a reaction’s activation energy  Enzymes – proteins that act as biological catalysts  Cells use enzymes to speed up chemical reactions that take place in cells  Enzymes provide a site where reactants can be brought together to react. Such a site reduces the energy needed for reaction.

 Substrates – the reactants of enzyme-catalyzed reactions  Enzymes work best at certain pH values. Many enzymes are affected by changes in temperature.  Enzymes play important roles in regulating chemical pathways, making materials that cells need, releasing energy, and transferring information.