Chapter 2

THE CHEMISTRY OF LIFE

A. MatterMaterial that takes up space.

1. ElementsPure chemical substances

composed of atoms.Examples?How many elements exist?How many of these elements are

essential to life?

Periodic Table of Elements

2. AtomThe smallest “piece” of an element

that retains the characteristics of that element.

Composed of 3 subatomic particles:ProtonsNeutronsElectrons

Characteristics of Subatomic Particles

Atomic number# protons in nucleus of an atom

(establishes identity of the atom)

Since most atoms are electrically neutral, atomic number indicates # of electrons as well.

Mass number# protons plus # neutrons in

nucleus of an atom

How can we determine the number of neutrons in an atom?# neutrons = atomic mass - atomic

# Determine # neutrons in a carbon

atom (atomic mass = 12; atomic # = 6).

# neutrons = 12 - 6 = 6Do all carbon atoms have the same

number of protons?Do all carbon atoms have the same

number of neutrons?

IsotopesAtoms having the same number of

protons, but differing numbers of neutrons.

Ex. Carbon isotopescarbon 12 (12C) 6 neutronscarbon 13 (13C) 7 neutronscarbon 14 (14C) 8 neutrons

Periodic table information on carbon:

Atomic mass given in table is average mass of all the element’s isotopes.

3. CompoundA pure substance formed when

atoms of different elements bond.The number of atoms of each

element is written as a subscript.Examples: CO2 carbon dioxide

H2O water

CH4 methane

C6H12O6 glucose

4. MoleculeSmallest piece of a compound that

retains characteristics of that compound.

The number of molecules is written as a coefficient.

Examples: 4CO2 4 molecules of carbon dioxide

2C6H12O6 2 molecules of glucose

6O2 6 molecules of oxygen

5. Chemical BondsType of bond formed is determined

by the number of valence electrons in the interacting atoms [octet rule].

a) Covalent bonds - form when atoms share electron pairs.can be nonpolar or polar form molecules

Nonpolar covalent bonds - electrons are shared equally between atoms.

Ex. methane

Polar covalent bonds - electrons are drawn more strongly to 1 atom’s nucleus than the other.

Form when less electronegative atoms bond with more highly electronegative atoms.

Ex. water

b) Ionic bonds - form when oppositely charged ions are attracted to each other. stronger than covalent bonds typically form salts

Ex. NaCl

c) Hydrogen bonds - form when opposite charges on two molecules are attracted to each other.weakest type of bond*

Ex. DNA H2O

B. The Importance of Water1. Properties Cohesion - the attraction of water

molecules for each other. Adhesion - the attraction of water

molecules for other compounds. High heat capacity – takes a great

deal of heat to raise the temperature of water.

High heat of vaporization - a lot of heat is required to evaporate water.

Exists as solid, liquid or gas - solid (ice) is less dense than liquid.

2. SolutionsA solution is a mixture of one or more

solutes dissolved in a solvent.If solvent is water, then it is an

aqueous solution.Water is a strong solvent because it

separates charged atoms or molecules.

3. Acids & Bases Acids - substances

that add H+ to a solution.

Bases - substances that remove H+ from solution.

pH scale is measure of acidity/alkalinity based on H+ concentration.

C. Major Organic MoleculesMolecules that contain carbon in

combination with hydrogen.

1. Carbohydrates contain C, H & O [ C O] function to store energy & provide

supportbuilding blocks (monomers) are

monosaccharides

Monosaccharides simple sugars containing 3 - 7 carbons.C, H, O ratio is 1:2:1

Disaccharides simple sugars composed of 2

monosaccharides linked together by dehydration synthesis.

Other common disaccharides: maltose (seed sugar) & lactose (milk sugar).

Polysaccharides complex carbohydrates made up of

hundreds of monomers linked by dehydration synthesis.

2. Lipids contain C, H, O [ C >> O]do not dissolve in water

Triglycerides (fats)composed of glycerol linked to 3

fatty acid chains by dehydration synthesis.

function to cushion organs, as insulation & in long-term energy storage (adipose tissue).

Phospholipids lipid bonded to a phosphate groupmajor component of cell membranes

Sterols lipids that have 4 interconnected

carbon ringsEx. Vitamin D, cortisone, estrogen &

cholesterol

Waxes fatty acids combined with

hydrocarbonshelp waterproof fur, feathers, leaves

& fruits

3. Proteinscontain C, H, O, N, (S)monomers are amino acids

Proteins have a 3-dimensional shape (conformation):

primary (1o) structure - amino acid sequence of polypeptide chain

secondary (2o) structure - coiling & folding produced by hydrogen bonds

tertiary (3o) structure - shape created by interactions between R groups

quarternary (4o) structure - shape created by interactions between two or more polypeptides

Examples:antibodieshemoglobin insulin & glucagonkeratinfibrin & thrombinspider silk (strongest natural fiber

known)enzymes (maltase, pepsin, lipase)

4. Nucleic Acids contain C, H, O, N, Pmonomers are nucleotides

DNA (deoxyribonucleic acid)5-carbon sugar is

deoxyribosenitrogenous bases

are A, G, C & Tdouble-stranded

helix held together by hydrogen bonds

is the genetic material

RNA (ribonucleic acid)5-carbon sugar is

ribosenitrogenous bases

are A, G, C & Usingle-strandedenables

information in DNA to be expressed