Chapter 6 The Chemistry of Life

Atoms and their interactions

Elements An element is a substance that can’t be broken down into simpler chemical substances –90 elements occur naturally –25 are essential to living organisms (table 6.1) –4 elements make up 96% of the mass of a human Carbon (C) Hydrogen (H) Nitrogen (N) Oxygen (O) Trace elements are present in living things in small amounts and play a vital role in maintaining healthy cells in organisms –Plants absorb them through their roots –Animals get them through food they eat

Atoms: The building blocks of Elements An atom is the smallest particle of an element that has the characteristics of that element An atom has a specific structure –Nucleus –Electron energy levels (orbitals)

Protons Neutrons Electron Energy Levels (orbitals) Nucleus

When electrons fill in energy levels they fill in a specific order. First orbital = 2 electrons Second orbital = 8 electrons Third orbital = 18 electrons Fourth orbital = 32 electrons

Isotopes of an Element An atom of the same element that has a different number of neutrons but same amount of protons and electrons –Carbon-12 ( 12 C) –Carbon-14 ( 14 C)

Compounds – a substance that is composed of atoms of two or more different elements that are chemically combined. –H 2 O –H 2 SO 4

Molecule – a group of atoms held together by covalent bonds and having no overall charge

Bonding Covalent – chemical bond formed when two atoms combine by sharing electrons Can form between atoms of the same element or atoms of different elements

Ionic – chemical bond formed by the attractive forces between two ions of opposite charge Compounds formed by ionic bonds are ionic compounds or salts, like NaCl or table salt.

Non-Polar Covalent Bonds Electrons are shared equally –A covalent bond between two atoms of the same element is always non-polar

Polar Covalent Bonds Electrons are not shared equally by the two atoms

Polar Covalent Molecule Formed from polar covalent bonds. Uneven distribution of charge Each molecule has a positive end and a negative end

Chemical Reactions Metabolism – all the chemical reactions that occur within an organism Chemical Equations – represent chemical reactions –Use symbols and formulas to represent each element NaOH + HCl → NaCl + H 2 O

Mixtures – a combination of substances in which individual components maintain their properties –Sand & sugar mixed together

Acid – substance that forms Hydrogen ions (H + ) in water –pH below 7 –HCl when dissolved in water forms H + ions and Cl - ions

Base – substance that forms hydroxide ions (OH - ) in water –pH above 7 –NaOH when dissolved in water forms Na + ions and OH - ions

Solutions – a mixture in which one or more substances (solute) are distributed evenly in another substance (solvent) –Sugar in water

Solute – substance to be dissolved Solvent – substance doing the dissolving Sugar & Water Sugar = Solute Water = Solvent

6.2 Water and Diffusion

Water is a polar molecule; therefore, water molecules bond The bond formed by negative and positive ends of polar molecules are called Hydrogen Bonds

Water –resists change in temperature –requires more heat to increase its temperature –helps maintain a steady environment when conditions fluctuate –important to cellular functions; it helps cells maintain an optimum environment –Expands as it freezes –Helps form soil by freezing in cracks of rocks and breaking them apart

Diffusion Diffusion – movement of particles from where there is a high concentration to where there is a low concentration

3 things affect rate of diffusion –Concentration More concentrated the substances, the more rapidly diffusion occurs –Temperature Higher temperature = faster diffusion (molecules moving faster) –Pressure Higher pressure = faster diffusion

Dynamic Equilibrium – continuous movement but no overall concentration change

6.3 Life Substances

The Role of Carbon in Organisms Carbon –Forms strong, stable, chemical bonds –4 bonding sites –Bonds 4 times for stability –Forms chains of almost unlimited length –They can form closed chains, rings, or branch wildly

Isomer – compounds that have the same molecular formula but different 3-D structure

Molecular Chains Polymer – a large molecule formed when many smaller molecules bond together –Formed by condensation –Broken apart by hydrolysis

Carbohydrates Organic compound composed of carbon, hydrogen, and oxygen –Simple carbs – simple sugar

Structure of Carbohydrates Monosaccharide – simplest carb Disaccharide – two monosaccharides bonded together –Bonding of glucose and fructose together makes sucrose (table sugar) Polysaccharide – largest carbohydrate molecules –Composed of many monosaccharide subunits Starch cellulose

Structure of Lipids Large proportion of C-H bonds Commonly called fats and oils Insoluble in water Cells use for energy storage, insulation, and protective coatings Major components of membranes

Structure of proteins Large polymer composed of amino acids –There are 20 common amino acids that make thousands of proteins –Amino acids bond to one another via a peptide bond –The number and order of amino acids in protein chains determine what protein it is Proteins come in large variety of shapes and sizes

Structure of Nucleic Acids A complex macromolecule that stores cellular information; it contains instructions used to form all of an organism’s enzymes and structural proteins –DNA –RNA

THE END