Chapter 2: The Chemistry of Life

2.1 The Nature of Matter

Atoms

• Atoms are the basic unit of matter and are made up of protons, neutrons, and electrons
• Protons and neutrons have the same mass but different charges
  • Protons have a positive charge (+)
  • Neutrons carry no charge at all
• An electron is a negatively charged particle (-)
• The nucleus is the center of the atom

Elements and Isotopes

• An element is a pure substance that consists entirely of one type of atom
  • Each element has a one- or two-letter symbol (C for carbon or Na for sodium)
  • An element’s atomic number is the number of protons in the atom
• Atoms of the same element that have different numbers of neutrons are isotopes
  • Protons + neutrons = mass number
  • Isotopes are named using their mass number
  • Some isotopes are radioactive

Chemical Compounds

• A compound is a substance formed by the chemical combination of two or more elements in definite proportions
  • The number of each element in a compound can be shown using chemical formulas
  • Ex: Since water has 2 atoms of hydrogen and 1 atom of oxygen, the chemical formula for water is H2O

Chemical Bonds

• @@The 2 main chemical bonds are ionic and covalent bonds@@

  • An ionic bond is formed when one or more electrons are transferred from one atom to another
  • An atom that loses electrons becomes positively charged, while an atom that gains electrons has a negative charge
  • Oppositely charged ions attract one another
  • A covalent bond is a bond between atoms in which the electrons are shared and is formed when the electrons travel around the nuclei of both atoms
  • Single covalent bond: atoms sharing 2 electrons
  • Double bond: atoms sharing 4 electrons
  • Triple bond: atoms sharing 6 electrons
  • @@Covalent bonds form structures called molecules@@
  • The molecule is the smallest unit of most compounds that displays all properties of that compound
  • In a water molecule, each hydrogen atom shares 2 electrons with the oxygen atom. So, each hydrogen atom is joined to the oxygen atom by a covalent bond.

  

2.2 Properties of Water

The Water Molecule

• @@Water is a polar molecule@@
  • A molecule in which the charges are unevenly spread out is said to be “polar”
• The pull between a partially positive hydrogen atom on one molecule and a partially negative oxygen atom on another is known as a hydrogen bond
  • @@Hydrogen bonds give water special properties such as cohesion, adhesion, and a high heat capacity@@
  • Cohesion: the attraction between molecules of the same substance
  • Adhesion: the force of attraction between different kinds of molecules
  • Heat capacity: the amount of energy needed to increase a substance’s temperature

Solutions and Suspensions

• Water is often part of a mixture
  • A mixture is made up of elements or compounds that are combined but not bonded together
• Two kinds of mixtures made with water are solutions and suspensions
  • A solution is a type of mixture in which all the components are evenly distributed. Contains one or more solutes in a solvent
  • A solute is what is dissolved
  • A solvent is what does the dissolving
  • A suspension is a mixture of water and non-dissolved material

Acids, Bases, and pH

• The pH scale is used to show the concentration of H+ ions in a solution
  • The scale ranges from 0 to 14
  • A solution with a pH of 7 is considered neutral
  • Solutions with a pH below 7 are acidic
  • Solutions with a pH above 7 are basic
• An acid is a compound that releases hydrogen ions in a solution; has a pH of less than 7
• A base is a compound that releases hydroxide ions in a solution; has a pH of more than 7
• A buffer is a compound that prevents sharp, sudden changes in pH

2.3 Carbon Compounds

The Chemistry of Carbon

• Carbon atoms have 4 electrons available for bonding, including @@hydrogen, oxygen, phosphorus, sulfur, and nitrogen@@ to form life’s molecules
• Carbon atoms can bond with one another
  • Carbon-carbon bonds can be single, double, or triple and can even close up on themselves to form rings

Macromolecules

• Macromolecules are made from thousands or even hundreds of thousands of smaller molecules called monomers
  • Monomers join to form polymers
• The four major groups of macromolecules are:
  • Carbohydrates: compounds made up of carbon, hydrogen, and oxygen atoms; a type of nutrient that is the main source of energy for the body
  • Simple sugars such as monosaccharides and disaccharides
  • Complex carbohydrates are the large macromolecules formed when simple sugars join together
  • Lipids: macromolecules that generally do not dissolve in water and are made mostly of carbon and hydrogen atoms; used to store energy and are parts of membranes and waterproof coverings
  • Common lipids include fats, oils, and waxes
  • Saturated and unsaturated
  • Nucleic acids: macromolecules containing hydrogen, oxygen, nitrogen, carbon, and phosphorus; function to store and transmit genetic information
  • Deoxyribonucleic acid (DNA) contains the sugar deoxyribose
  • Ribonucleic acid (RNA) contains the sugar ribose
  • Proteins: macromolecules that contain carbon, hydrogen, oxygen, and nitrogen; needed by the body for growth and repair
  • Amino acids are compounds with an amino group on one end and a carboxyl group on the other end

2.4 Chemical Reactions and Enzymes

Chemical Reactions

• A chemical reaction is a process that changes or transforms one set of chemicals into another set of chemicals
  • Reactants are the elements or compounds that go into a chemical reaction
  • Products are the elements or compounds that come out of a chemical reaction

Energy in Reactions

• Chemical reactions that give off energy often happen on their own, while chemical reactions that take in energy will not happen without a source of energy
  • Activation energy is the energy that is needed to get a reaction started

Enzymes

• A catalyst is a substance that speeds up the rate of a chemical reaction by lowering a reaction’s energy rate
  • Enzymes are proteins that act as catalysts in living things
  • The reactants of enzyme-catalyzed reactions are known as substrates
  • The substrates bind to a site called the active site
  • Temperature, pH, and other molecules can affect how enzymes work