Carbohydrates
Provide energy for living things
Are composed of atoms of carbon, hydrogen and oxygen on a 1:2:1 ratio. All carbohydrates
have the same basic formula of (CH2O)n
Carbohydrates are classified according to their size and complexity
Monosaccharides
Simple sugars
They are the building blocks of all other carbohydrate molecules. They are monomers: smaller
molecules that bond together to form long chains called polymers.
The most common monosaccharides have the formula C6H12O6. The three most common
monosaccharides are:
 Glucose: the only sugar living things can use for energy
 Fructose: the sugar found in fruit
 Galactose: a sugar found in milk. It is a mirror image of glucose
These three molecules are isomers. They have the same chemical formula but very different
structures. Because they have the same formula, they can be converted easily from one form to
another.
Their structures are:
Glucose
Fructose
Galactose
Disaccharides
Disaccharides are double sugars. They are formed when two monosaccharides bond together.
When the two monosaccharides bond, water is given off in the process. This is called
condensation or dehydration synthesis. They are isomers as well. The loss of a water molecule
gives all disaccharides the formula C12H22O11. To reverse dehydration synthesis and break a
disaccharide down into its individual monosaccharides, just add water to the molecule. This
process is called hydrolysis.
The three common disaccharides are
 Maltose: glucose + glucose
o Malt sugar
 Used in making beer, candy and chocolate malts

Sucrose: glucose + fructose
o Table sugar
 Most common sources are sugar cane, beets and corn

Lactose: glucose + galactose
o Milk sugar
 A person who is lactose intolerant does not have the ability to digest this
sugar
 About 60% of Americans are lactose intolerant
galactose
glucose
Dehydration Synthesis of Maltose
Glucose
+
Maltose
Glucose
Polysaccharides
Long chains of monosaccharides
There are many different polysaccharides, but the most common are:
 Amylose (starch): long chain of glucose molecules
o Produced by plants in photosynthesis
o The primary source of glucose in both plants and animals
o Is not sweet

Glycogen: long chain of glucose molecules
o Made by animals
o It is made in the liver and is the only way an animal has of storing extra glucose
 Glycogen is stored in the liver and in muscle cells
 When the body needs glucose, glycogen is broken down into individual
glucose molecules

Cellulose: long chain of glucose molecules
o Found in the cell walls of plants
o Humans and many other animals cannot digest cellulose
 Is the source of “fiber” in our diet

Chitin: chain of glucose
o Makes up the exoskeletons (shells) of insects and shellfish
Protein
Proteins provide structural support in living things and they build and repair damage done to
cells and tissues.
Hair, skin, nails and muscles are all made of protein.
Amino acids are the building blocks of proteins. All protein molecules are folded chains of
amino acids.
 An unfolded chain of amino acids is called a polypeptide.
 The shape of a protein determines its function. If the shape of a protein is altered, its
function will be affected.
Protein structure
All proteins have the following elements of their structure
 Primary structure: the order of the amino acids in the polypeptide chain
o Determines the identity of a protein just as the order of the letters determines the
meaning of a word. EX. DOG and GOD. Same letters, very different meaning.
 Secondary structure: the first fold in the polypeptide
 Tertiary structure: the second fold in the protein
Amino acid Structure
All amino acids have the same basic structure:
R group is the only part of an amino acid molecule that can change
Observe the only difference between these two amino acids is what is bonded at the location of
the R group:
Glycine
Isoleucine
Amino acids bond together to form disaccharides (chains of 2 amino acids) and polysaccharides
(chains of many amino acids). They also bond using dehydration synthesis because they release
a water molecule in the process, and polysaccharides can be broken into individual amino acids
by adding water in hydrolysis.
 The bond that holds amino acids together in a polypeptide of a protein is called a
peptide bond and is found only in proteins.
Dehydration synthesis of amino acids
Enzymes

Enzymes are proteins that act as catalysts
 catalysts speed up a chemical reaction by either lowering the amount of energy
needed to begin the reaction (the activation energy) or by lowering the temperature
the temperature at which the reaction takes place.
 catalysts do not take part in the reaction so they are neither changed or
consumed in the reaction
 enzymes are reusable

The shape of an enzyme is very important. Every enzyme is designed to work with one
specific molecule (called the substrate).
 The enzyme and its substrate are substrate specific. The enzyme and its substrate are
shaped so that they fit together like a lock and a key (or two pieces in a puzzle). If
the shape of the enzyme is changed (it is denatured) it will no longer fit with its
substrate and will not catalyze the reaction.
 The spot where an enzyme bonds to its substrate is called the active site.
Denaturing the enzyme either changes the shape of the active site or its
location so the enzyme and its substrate physically cannot bond.
Enzymes get their names from their substrates. The name of every enzyme (except for one) ends
in the suffix “-ase”.
 Example: 1. Maltase breaks down maltose to two glucose molecules
2. Amylase breaks down starch to maltose molecules
3. Peptidase breaks polypeptides down to dipeptides and amino
acids
 The exception to this rule is the enzyme pepsin. It breaks down protein.

Since enzymes are proteins, they are denatured by the same things that denature other
proteins:
 high temperature
 low (acid) pH

If an enzyme is denatured it is destroyed permanently. It will no longer be able to catalyze
the reaction it was intended to catalyze, so that reaction will not take place. If too many
reactions are stopped by denaturing enzymes an organism will die.
Lipids
Lipids store energy, insulate the body and protect body organs
 Lipids are made of carbon, hydrogen and oxygen
 Lipids are the only organic molecules that are insoluble in water
 Lipids are classified into two groups:

triglycerides: 1 three carbon glycerol molecule bonded to three fatty acid chains.
Every extra glucose molecule that is consumed is broken into two glycerol
molecules and thus forms two molecules of fat.
 triglycerides can be divided into three groups:
 fats
 come from animals
 solid at room temperature
 oils
 come from plants
 liquid at room temperature
 waxes
 made when an alcohol group bonds to the fatty acids
 found in both plants and animals and can be man-made
This is the structure of a basic triglyceride:
Animal product
Plant product
Please note that the only difference between a saturated and an unsaturated fat is the presence of
the double bonded carbon in the fatty acids of the unsaturated fat. The presence of the double
bonded carbon makes unsaturated fats easier to digest.

steroids: a molecule composed of two interlocking four carbon rings
 also insoluble in water
 one of the most common steroids is cholesterol which can be formed
from triglycerides
 there are two types of cholesterol:
 HDL: “good cholesterol”. Helps maintain the membranes
of our cells
 LDL “bad cholesterol”. Carried in our blood. Forms
deposits on the inside of blood vessels and can eventually
clog the vessels leading to heart attack or stroke.
This is the basic structure of a steroid molecule:
Please note that it is the carbohydrates in our diet that form fat deposits in our bodies. Dietary fat
is converted into cholesterol.
Nucleic acids
Nucleic acids are composed of carbon, hydrogen, oxygen, nitrogen and phosphorous. These
elements are organized into small units called nucleotides. Nucleotides are the building blocks
of nucleic acids
There are two types of nucleic acids:
DNA: deoxyribonucleic acid. It is found in the cell’s nucleus . It controls all of the cell’s
activities
RNA: ribonucleic acid. It is found in the cell’s cytoplasm. It makes protein.