Life Substances
The Role of Carbon in Organisms
 A carbon atom has four electrons available for bonding in its outer energy level.
 In order to become stable, a carbon atom forms four covalent bonds that fill its
outer energy level.
 Carbon can bond with other carbon atoms, as well as with many other elements.
 When carbon atoms bond to each other, they can form straight chains, branched
chains, or rings. These chains and rings can have almost any number of carbon
atoms and can include atoms of other elements also.
Double Bonds = When each atom shares two electrons, a double bond is formed.
 A double bond is represented by two bars between carbon atoms.
Triple Bonds = When each atom shares three electrons.
 Triple bonds are represented by three bars between atoms.
Isomers = Compounds that have the same simple formula but different three-dimensional
structures.
Example = glucose & fructose = C6H12O6 (see book page 162)
Molecular Chains
 Carbon compounds vary greatly in size.
 Some compounds contain just one or two carbon atoms; others contain tens,
hundreds, or even thousands of carbon atoms.
Macromolecules = A giant molecule of living matter formed by the joining of smaller
molecules, or one containing hundreds (or more) carbon atoms.
 Examples are polysaccharides, proteins, and nucleic acids
 Cells build macromolecules by bonding small molecules together to form
chains called polymers.
Polymer = A large molecule formed when many smaller molecules bond together.
 Condensation is the chemical reaction by which polymers are formed. (It
occurs by removing a –H and an –OH from the two groups; thus, removing a
water, H2O, molecule.)
 The subunits become bonded by a covalent bond.
 Hydrolysis is a method by which polymers can be broken apart. (Done by
adding water to the compound – much like dissolving sugar in solution.)
Carbohydrates = An organic compound composed of carbon, hydrogen, and oxygen
with a ratio of about 2 H atoms and1 O atom for every 1 C atom.
 Carbohydrates are used by cells to store and release energy.
Monosaccharide = The simplest type of carbohydrate, which is a simple sugar.
Examples are glucose and fructose.
Disaccharide = When two monosaccharide molecules link together to form a two-sugar
carbohydrate.
Example = sucrose (table sugar) formed by combining glucose and fructose
Polysaccharides = The largest carbohydrate molecules. They are polymers composed of
many monosaccharide subunits.
Examples = starch, glycogen, and cellulose
 Starch consists of highly branched chains of glucose units.
o It is used as food storage by plants in food reservoirs such as seeds
and bulbs.
 Mammals store food in the liver in the form of glycogen.
o It is a glucose polymer similar to starch but more highly branched.
 Cellulose is made of long chains of glucose units hooked together
somewhat like a chain-link fence.
o It forms the cell walls of plants and gives plants structural support.
Lipids = Organic compounds that have a large proportion (much greater than 2 to 1) of
C–H bonds and less oxygen than carbohydrates.
Example = a lipid in beef fat has the formula C57H110O6
 Lipids are commonly called Fats and Oils
 They are insoluble in water b/c their molecules are nonpolar
 They are extremely important for the proper functioning of organisms
 Cells use lipids for energy storage, insulation, and protective coatings
 They are the major components of the membranes that surround all living
cells
 The most common type of lipid consists of three fatty acids bound to a
molecule of glycerol
Proteins = A large, complex polymer composed of carbon, hydrogen, oxygen, nitrogen,
and usually sulfur.
 Proteins are essential to all life.
 They provide structure for tissues and organs and carry out cell metabolism.
 Amino acids are the basic building blocks of proteins.
o There are 20 common amino acids.
o They are linked together when an –H from one amino acid and an
–OH group from another amino acid are removed to form a water
molecule.
o The covalent bond formed between the amino acids is called a
peptide bond.
o A long chain of amino acids is called a polypeptide.
 Proteins are composed of two or more polypeptides.
 Proteins vary more in structure than any other class of organic molecules.
 The number and order of amino acids in protein chains determine the kind of
protein.
 Proteins are the building blocks of many structural components of organisms
(such as hair, nails, horns, hoofs, etc.)
Enzymes = A protein that changes the rate of a chemical reaction.
** see page 166 in book **  “Lock–and–Key”
 They are catalytic proteins.
o A catalyst is a chemical agent that changes the rate of a reaction
without being consumed by the reaction
 They are important proteins found in living things and are essential for the
functioning of any cell.
 They are involved in nearly all metabolic processes.
 They speed the reactions in digestion of food.
 They also affect synthesis of molecules, and storage and release of energy.
 An enzyme speeds up a chemical reaction by lowering the activation energy.
o The reactant an enzyme acts on is referred to as the enzyme’s
substrate.
o Only a restricted region of the enzyme molecule actually binds to
the substrate. This region, called the active site, is typically a
pocket or groove on the surface of the protein.
o The specificity of an enzyme is attributed to a compatible fit
between the shape of its active site and the shape of the substrate.
Nucleic Acids = A complex macromolecule that stores cellular information in the form
of a code.
 They are also necessary for life.
 They are polymers made of smaller subunits called nucleotides.
o Nucleotides consist of carbon, hydrogen, oxygen, nitrogen, and
phosphorus atoms arranged in three groups:
1. a base,
2. a simple sugar, and
3. a phosphate group.
(see picture in book, page 167 – figure 6.23)
o DNA = deoxyribonucleic acid
 DNA is the master copy of an organism’s information code.
 The information coded in DNA contains the instructions
used to form all of an organism’s enzymes and structural
proteins.
 Thus, DNA forms the genetic code that determines how an
organism looks and acts.
o RNA = ribonucleic acid
 RNA is a nucleic acid that forms a copy of DNA for use in
making proteins.
Questions: (answer on the back of this sheet)
A. List three important functions of lipids in living organisms.
B. Describe the process by which polymers in living things are formed from smaller
molecules.
C. How does a monosaccharide differ from a disaccharide?
D. Enzymes are proteins that facilitate chemical reactions. Based on your knowledge of
enzymes, what might the result be if one particular enzyme malfunctioned or was not
present?
Macromolecule
Monomer
Examples
Function
Monosaccharides
Glucose, Fructose
Disaccharides
Polysaccharides
Sucrose
Starch,
Glycogen,
Cellulose
Lipid
Fatty Acids
Fats, Oils, Waxes,
Steroids
(long-term) Energy Storage,
Insulation,
Protective Coatings
Component of Cell Membranes
Protein
Amino Acids
Enzymes
Structure for Tissues & Organs,
Carry Out Metabolism
Nucleic Acid
Nucleotides
DNA, RNA
Code for Making Enzymes &
Structural Proteins
Carbohydrate
(short-term) Energy Storage
Food Storage in Plants (seeds, bulbs)
Food Storage in Liver of Mammals
Component of Plant Cell Walls
(structure, support)