Chapter 5
Enzymes, Coenzyme and Energy
Biology 100
Spring 2009
Energy

All living things require energy.
◦ Nutrients are one source of energy, as well as
being molecules organisms require to grow,
reproduce or repair

Biochemical reactions are the processes
used for the formation, breakdown and
rearrangement of molecules to provide
organisms with energy
Activation Energy

Activation Energy is the required input of
energy to make a reaction start
Catalyst

A catalyst is a chemical that speeds up the
reaction but is not used up in the reaction
◦ Lowers the activation energy needed to start
a reaction
◦ Is not used up during the reaction
◦ Is unchanged after a reaction
Enzymes

Enzymes act as catalysts. Enzymes are
proteins that speed up a rate of reaction
◦
◦
◦
◦
Found in cells throughout the body
Lowers activation energy
Enzymes will end in –ase
SPECIFIC!
Enzymes
How Enzymes Work

Each enzyme has a specific size and 3-D
shape
◦ Each enzyme is going to fit with a certain
substrate (molecule enzyme connects to)
How Enzymes Work
When the enzyme and substrate are
connected, it is known as enzyme-substrate
complex
 The binding site is where the enzyme
physically attaches itself to the substrate
 The active site is where the enzyme will
cause a specific part of the substrate to
change

Cofactors/Coenzynes

Some enzymes need an additional
molecule to carry out the process
◦ Cofactors are inorganic ions or organic
molecules that serve an enzyme helpers
◦ Coenzymes are organic molecules that
function as a cofactor
 May be certain amino acids, nitrogenous bases, and
vitamins
Cofactors
Turnover Number

The number of molecules of substrate
with which a single enzyme can react at a
given time (ex. reactions/minute) is known
as the turnover number
◦ Can be quite large compared to uncatalyzed
reeactions
◦ Can depend on the environment
Environment

Temperature can have a huge impact on
turnover rate
◦ a higher temperate will increase the rate of
molecular motion, to a certain extent
◦ Too high of temperatures may cause the
enzyme to change its shape, this is known as
denaturing, where a protein structure is
permanently changed
Environment

Optimum temperature is when the rate of
formation of the enzyme-substrate
complex is fastest
Environment

pH also affects the rate of enzymesubstrate complexes
◦ Most enzymes have an optimum pH of around
7 (neutral)
 However, some prefer acidic or basic conditions
Competition

Enzymatic competition is where there are several
kinds of enzymes available to combine with the
same kind of substrate molecule
◦ The substrate acetyl can be acted upon by three
different enzymes: citrate synthetase, fatty acid
synthetase, and malate synthetase
Fig. 5.7,
pg.103
Gene Regulator Proteins

Gene Regulator Proteins are chemical
messengers that inform the genes of the
cell’s need for enzymes
◦ Gene-repressor proteins decrease protein
production
◦ Gene-activator proteins will increase protein
production
Fig. 5.7, pg.103
Inhibitor

Inhibitor is a molecule that attaches itself
to an enzyme and interferes with the
enzymes ability to form an enzymesubstrate complex
◦ Competitive Inhibition
◦ Negative-Feedback Inhibition
Competitive Inhibition

In competitive inhibition an inhibitor has a
shape that is closely resembling the normal
substrate of an enzyme
◦ Enzyme becomes ineffective
Negative-Feedback Inhibition
In negative-feedback inhibition is a process
where the output of a system acts to
oppose changes to the input of the system
 Allosteric Regulation is the regulation of an
enzyme or other protein by binding an
effector molecule at the protein's
allosteric site (a site other than the active
site)
http://highered.mcgrawhill.com/olc/dl/120070/bio10.swf
