Biology 12

UNIT 1 Investigation

DESIGN YOUR OWN

ASSESSMENT

After you complete this investigation,

• assess your procedure by having a classmate try to
  duplicate your results;


• assess your results by comparing your data with those
  found by other students.

98 MHR • Unit 1 Metabolic Processes

Enzymes and Reaction Rate

Background

In Unit 1, you have seen that living cells rely

on enzyme activity for metabolic processes.

The different enzymes allow a reaction to move

forward more quickly by lowering the activation

energy required for the reaction to proceed.

Enzymes are proteins that catalyze the rate of the

reaction by providing a lower-energy pathway.

The study of catalysts and reaction rates

provides insight into how cells use enzymes

effectively. The rate of a reaction is measured

in one of two ways: by finding the amount of

reactant (substrate) consumed, or by the amount

of product formed. You used this second

method in your experimental work with

peroxidase and hydrogen peroxide.

Peroxidase is an enzyme that is found in

peroxisomes, specialized organelles in the cell.

The enzymes responsible for glycolysis are

dissolved in the cytosol. Other enzymes are

found embedded in membranes. Enzymes on

the inner membrane of the mitochondrion or

the thylakoid membrane of the chloroplast are

crucial to the energy-transforming reactions that

take place here.

One strategy that maximizes the efficiency of

enzyme activity is extensive folding of the

membrane structures. The simple outer

membranes do not contribute to the energy

reactions. The active membranes are extensively

folded, however, allowing many copies of the

enzymes to participate in reactions at the same

time. This strategy effectively speeds up the rate

of the reaction. Embedded in the membrane,

these enzymes are in a different phase from the

substrate. The effect is similar to increasing the

surface area of a reactant, like chopping wood

before burning it to make it burn faster.

As proteins, enzymes each have a distinctive

shape. Factors affect enzyme shape by

disrupting bonds and promoting different

folding patterns. A differently folded enzyme

may become insoluble, precipitating out of the

cytosol and out of the cell’s metabolic processes.

Environmental factors that can affect enzyme

shape include temperature, radiation, pH, and ion

concentration. While a raw potato has working

peroxidase enzymes, cooked potatoes do not.

The concentration of ions, including pH, can

affect the bonds within an enzyme. Metal ions

can act as cofactors, but adding more metal ions,

such as Cu^2 +or Ag^2 +can disrupt the natural

folding pattern of the enzyme.

Pre-lab Focus

How can you measure the rate of an enzyme

reaction?

What is a substrate and what conditions in the

cell control the amount of substrate available?

How is the shape of an enzyme important and

what are factors that could affect it?

Problem

Cell metabolism relies on enzymes that catalyze

biochemical reactions in the cell. Many factors

contribute to the enzyme’s effective activity

within the cell, including temperature and pH.

What is another factor?

Hypothesis

Based on your understanding of metabolic

processes, formulate a hypothesis that predicts

the impact of a specific factor on the rate of an

enzyme reaction.

Materials

CuSO 4 (copper(II) sulfate) graduated cylinders

AgNO 3 (silver nitrate) droppers or pipettes

H 2 SO 4 (sulfuric acid) pH paper or probes

HCl (hydrochloric acid) test tubes

NaCl (sodium chloride) test tube rack

safety goggles test tube holder

aprons test tube brush

gloves beakers

hot water bath beaker tongs

ice bath substrate

thermometers or enzyme

temperature probes

Safety Precautions

Check WHMIS charts to identify appropriate

safety equipment when using chemicals.

Avoid allowing a hot water bath to boil

vigorously, which can cause test tubes to

break. Use a moderate heat setting.

Use test tube holders and beaker tongs to

move hot glassware.