Chapter 6The 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 electronsSecond orbital = 8 electronsThird orbital = 18 electronsFourth 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 (12C)– Carbon-14 (14C)

Compounds

• – a substance that is composed of atoms of two or more different elements that are chemically combined.– H2O

– H2SO4

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 + H2O

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 & WaterSugar = 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