Biochemistry: Chemical Reactions and Organic Macromolecules

1. Chemical reactions- a process where one or more substances called the reactants are converted
into one or more substances called products by forming new chemical bonds and/or breaking
existing chemical bonds.
a. In many cases, chemical reactions are reversible in which case products can be converted
into reactants.
b. Important chemical reaction types:
i. Anabolic reactions- reactions where many small molecules are linked together by the
newly formed bonds to form large molecules.
1. Anabolic reactions store energy in the newly formed bonds.
ii. Catabolic reactions- reactions where large molecules are broken down into small
molecules by breaking lots of bonds in the large molecules.
1. Catabolic reactions release energy from the broken bonds.
c. Many chemical reactions occur in the body simultaneously, and a way to summarize all
that activity is in the term metabolism. Metabolism- is the sum of all the chemical
reactions occurring in the cells and tissues of the body.
i. A good way to think of metabolism is to think about it as balancing your body's
energetic checkbook. You consider all the anabolic and catabolic reactions occurring
and calculate the amount of energy (calories) you need for your body to function.
You can compare this value to the energy you consume and see if you consumed
more calories than you need or if you did not consume enough calories to support
your body's needs.
d. Factors that alter the rate of chemical reactions:
i. Reactant and product concentrations
1. Law of mass action- according to the law of mass action, chemical reactions
automatically respond to changes in reactant and product concentration to
return to equilibrium.
a. ↑ concentration of reactants or ↓ concentration of products =
reaction moves forward = reactants use to produce more product
b. ↓ concentration of reactants or ↑ concentration of products =
reaction moves in reverse = products used to produce more reactant
c. This can be used by the body to control the direction of a chemical
reaction.
ii. Temperature
1. Just like diffusion, the rate (speed) of chemical reactions depends on the
temperature.
2. ↑ Temperature = ↑ rate (speed) of chemical reactions.
3. ↓ Temperature = ↓ rate (speed) of chemical reactions.
iii. Catalysts
1. Activation energy- the energy required to get the chemical reaction started.
This varies from reaction to reaction.
2. A catalyst is a substance that increases the rate (speed) of a chemical reaction
by reducing the activation energy required to get the reaction started.

3. Inorganic catalysts- catalysts that are not proteins or other types of organic
molecules.
4. Organic catalyst- protein catalysts called enzymes.
2. Introduction to Organic Molecules
a. Organic molecules are molecules containing mostly carbon and hydrogen. These organic
molecules are the building blocks of cells and, as a result, all living things.
b. Small, individual organic molecules are called monomers.
c. In many cases in cells, the organic molecule monomers are linked together (polymerized)
into long chains of monomers called polymers.
d. When individual monomers are linked together, a water molecule is lost in a process called
dehydration synthesis. Dehydration synthesis reactions are the reactions that make
polymers from many monomers in the cells and tissues of the body. See slide 8 for an
example of a dehydration synthesis reaction.
e. Sometimes the polymers need to be broken down into the individual monomers. Water
must be added to the reaction to break the bonds between the monomers and break apart
the polymer in a process called hydrolysis. Hydrolysis reactions are the reaction that
breaks apart polymers in the cells and tissues of the body. See slide 8 for an example of a
hydrolysis reaction.
f. There are four classes of organic molecules that make up cells which will be discussed in
detail in the remaining biochemistry lectures:
i. Carbohydrates
ii. Lipids
iii. Nucleic acids
iv. Proteins