Lesson 13 – Enzyme
Activity
Learning Goals

Learn how enzyme activity can be affected
by:

environmental conditions

regulation by the cell

Observe/inquire about enzyme activity
using a PEOE.

Enzyme Function Summary

Catalyze reactions in living
organisms

lower Ea

function in anabolic and catabolic
pathways

Induced fit model

3D shape (conformation) a result of
their amino acid sequence.
Optimal Environments

If an enzyme’s function is dependent on
its folding and shape, and we know
certain variables can affect the shape
of the enzyme…… Well, what could we
possibly conclude?
Temperature Affects Activity

At first, increasing temperature will
increase enzyme activity, as more kinetic
energy is provided to molecules (more
collisions).

After reaching an optimum, increases in
temperature begin to denature the enzyme,
breaking its secondary, tertiary and
quaternary structure

Eventually, complete loss of function will
occur when all enzyme molecules are
denatured.
The activity curve for a human enzyme shows optimal
function at 37oC, but some enzymes in certain
archaebacteria function at temperatures even above
100oC!
pH Affects Activity

Folding (and thus activity) is also affected by
pH, as hydrogen ion concentration will affect
amino acid interactions.

Pepsin works best at pH 2

where does it function?

Trypsin works best at pH 8

where does it function?
Other Ways to Affect Rate

A limiting factor is the factor that is
preventing the reaction from occurring at
a faster rate - for example, the
substrate, or the enzyme concentration
could be limiting.

If we increase the concentration of the
limiting factor (eg. substrate
concentration), we will increase the rate
of reaction up to when that factor is no
longer limiting (enzyme concentration is
now limiting).
Cofactors/Coenzymes

Some enzymes require non-protein cofactors
for proper biological function.

Some cofactors are inorganic, such as metal
ions like Zn2+, Mg2+, Cu+, or Fe2+

Some cofactors are organic, and are called
coenzymes - we will see some good
examples of these in the next unit. Many
coenzymes are synthesized from the vitamins
we get in our diet.
Enzyme Inhibition

A variety of molecules can inhibit enzyme
activity by interfering with substrate binding
or the shape of the enzyme itself.

Competitive inhibitors bind directly to the
active site and prevent substrate binding
(often these are structurally similar to the
substrate). Some poisons work this way (eg.
cyanide).

Non-competitive inhibitors bind to different
sites (allosteric sites) and affect the shape
of the active site.
Enzyme Activation

Other molecules can be
activators of enzyme
activity, in effect doing the
opposite of what an
inhibitor does.
Regulation

Cells can actually control the activity
rate of their enzymes in two primary
ways:

Regulating production of enzyme itself
(too little reaction, create more
enzyme…)

Allosteric regulation (using inhibitors
and activators)
Feedback Inhibiation

Most reactions in living organisms are not
completed in one step, and involve
biochemical pathways - sometimes the
product from one step can become the
substrate of the next.

In some cases, the product of a later reaction
can act as an allosteric inhibitor for an earlier
enzyme. This is termed feedback inhibition.
http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::
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ical+Pathways
Review

What factors influence enzyme activity?

Why does temperature affect enzyme activity?

What is a cofactor? Do some research to find an example of one.

How do competitive and non-competitive inhibition differ?

What is feedback inhibition?

Enzymes in the testicles of males are responsible for both sperm and hormone
production. Some of these enzymes have an optimal temperature of 33ᵒC


What anatomical features help the testicles maintain this temperature?

How does this relate to the idea that structure and function are related?