The Chemistry of LifeChapter 2

2-1 Element

Substance that cannot be broken down into simpler substances

91 occur naturally– #1-92 found naturally; except 43, 61– #93 and above are synthetic– Only 25 needed for life

Only 4 elements make up 96% of human mass: C, H, O, N

4% are Ca, P, K, S, Na, trace elements

Atoms

Smallest particle of an element Structure

– Center is the nucleus, contains protons (+) and neutrons (0)

– Electrons (-) form a cloud around the nucleus

Electron energy fields

Electrons travel around the nucleus in energy levels– 1st holds 2 electrons– 2nd holds 8– 3rd holds 18

Atoms have equal numbers of electrons and protons (make up a neutral atom)

Isotopes

Atoms of the same element with different numbers of neutrons

Ex carbon-12 and carbon-14

Compound

Substance composed of atoms of different elements chemically combined

3 ways to combine elements– Covalent bond– Ionic bond– Hydrogen bond

Covalent bonds

Atoms share electrons equally Bonding makes atoms more stable Covalent bonds produce molecules

– Sugar– Fat – Protein– Water

Covalent bond

Ionic bonds

Atoms combine by gaining or losing electrons in the outer energy levels

Ions-atoms that have gained or lost electrons

Attractive force between ions of opposite charges produces ionic bond

Important for biological processes– Transmission of nerve impulses– Muscle contraction

Ionic Bond

Hydrogen bonds

Bond between hydrogen of one molecule and the negative ion of another molecule

Strongest MOLECULAR bond Important in biological molecules like

protein or nucleic acids

Hydrogen bonds

Mixture

Combination of substances in which individual substances retain their own properties– Stir sand and sugar together– do not combine chemically– Do no change

Solution

A mixture in which one or more substances are distributed evenly in another substance– Kool-Aid is evenly distributed in water– Kool-Aid (solute) will dissolve– Water (solvent) does the dissolving

2-2 Importance of water

Makes up 70%-95% of most organisms

Used to transport materials in organisms

Water molecule

Water’s polarity

Covalent bonds between oxygen and hydrogen of water do not share electrons equally– Oxygen attracts electrons more strongly– Oxygen will be more negative– Hydrogen will be more positive– Creates an unequal distribution of

charge or polarity– Gives water its dissolving power

Other water properties governed by hydrogen bonding

Adhesion-an attraction between molecules of different substances

Cohesion-attraction between molecules of the same substance

High specific heat-water resists changes in temperature; must absorb more heat to increase in temperature

pH

Measures amount of H+ ions in solution (the concentration of H+ determines whether a solution is acidic or basic)

Scale ranges from 0 to 14 0-6.9 is acidic 7.1-14 is basic

pH scale

Acids

Forms hydrogen ions (H+) in water Hydrogen chloride added to water

makes H+ and Cl- As a solution this would be

hydrochloric acid (HCl)

Bases

Form hydroxide ions (OH-) in water Sodium hydroxide in water forms

Na+ and OH-

Buffers

Weak acids or bases that react with strong acids or bases

Prevent sudden changes in pH

2-3 Carbon atoms

When bonded to each other can form– Straight chains– Branched chains– rings

Can also form isomers– Compounds with the same formula but

different 3-D arrangement

Carbon structures

Macromolecules

Contain ten, hundreds, or thousands of carbon atoms

Used by cells for biological processes Made by bonding small units

together to make polymers

Carbohydrates

Store and release energy Composed of C, H, and O Single unit called monosaccharide Largest are polysaccharides Examples

– Starch-branched chain of glucose in plants

– Glycogen-highly branched chain of glucose in animals

Carbohydrates

Lipids

Contain large amounts of C, H, but less amounts of O

Called fats and oils Insoluble in water Used for long-term energy storage,

insulation, protective coverings Major components of membranes

Lipids

Proteins

Build structure and carry out metabolism

Made of C, H, O, N, S Basic units are amino acids (20)

– Linked by condensation reactions– Release water as waste product– Covalent bond between amino acids is

called a peptide bond– Protein determined by order of acids

Proteins

Building blocks structural components of organisms

Important for– Muscle contractions– Transport of oxygen– Immunity– metabolism

Protein (peptide bond)

Proteins

Enzymes– Speeds up metabolic reactions– Help with food digestion– Synthesis of molecules– Storage and release of energy

Nucleic Acids

Stores information in code form Units called nucleotides Made of C, H, O, N, P arranged in 3

groups– Base– Simple sugar– Phosphate group

Nucleic Acids

DNA-deoxyribonucleic acid– Master copy of organism’s code– Forms genetic code– Contributes to physical traits

RNA-ribonucleic acid– Copy of DNA– Used for protein synthesis

Nucleic acid

2-4 Chemical reactions

In organisms are called metabolism Break down and build molecules Atoms are never created or

destroyed, just rearranged Reactants are on the left Products are on the right

Chemical reaction

Energy in reactions

Some reactions release energy and are called spontaneous (exothermic)

Some require energy and must get it from another source (endothermic)

Activation energy is the energy required to get a reaction started

Chemical equilibrium

Can be seen in reactions that are reversible

Equilibrium is reached when the reaction takes place at an equal rate in both directions

So both reactants and products are made at the same time

Enzymes

Proteins that act as catalysts in reactions

Work by lowering the activation energy

So not as much energy is needed to get the product

Enzymes

Enzyme regulation

Enzymes can be controlled or affected by– pH– Temperature– Other proteins