Birds & Aging
• Many birds appear not
to show the effects of
cellular senescence (i.e.
cells stop reproducing)
• This failure to show the
physical effects of aging
may be due to high
levels of peroxidases
Peroxides
• Highly reactive, strong
oxidizers
• When broken down slowly,
may produce FREE
RADICALS, which can
damage DNA and other
cellular structures
• While some free radicals
may help the immune
system, others may lead to
oxidative stress
Peroxidases
• Enzymes that reduce
the activation energy
required to cause the
decomposition of
peroxides
• Rapid breakdown =
fewer free radicals
Catalase
• Found in most forms of life
on Earth
• One molecule of catalase
can convert 40 million
hydrogen peroxide
molecules/sec
• 500 amino acid long
protein, containing four
heme (iron) rings held
together in the quaternary
structure
• Iron in heme rings reacts to
pull electrons away from
H2O2 bonds, causing it to
disassociate
LAB: Decomposition of Hydrogen
Peroxide via Catalase
• Purpose: To assess the
effects of enzyme
concentration, ambient
temperature and pH on
the rate of
decomposition of
hydrogen peroxide
• Method: Measure rate
of pressure change
(kPa/sec)
Concentration and Reaction Rate
• Because the
relationship between
substrate and enzyme is
so specific, changing
the number of enzymes
reacting with the
substrate (or vice versa)
may affect the rate of
reaction
• Ex: Vmax
Temperature and Reaction Rate
• Temperature is a
measurement of
molecular speed
• At a lower temperature,
molecules collide less
frequently
• At higher temperatures
molecules collide more
frequently
• Enzymes tend to have an
optimal temperature at
which they function
pH and Reaction Rate
• Enzymes have specific
pH ranges in which they
tend to function most
effectively
• Outside of this range,
enzymes can denature,
causing them not to fit
with their substrates
• If enzyme does not fit,
EA is too large for the
reaction to occur
GROUPS & VARIABLES
• GROUPS 1 & 4 –
Concentration
• GROUPS 2 & 5 –
Temperature
• GROUPS 3 & 6 – pH
• Dependent Variable For
All = slope (m) for plot
of pressure v. time
Lab Notes
• Take 20 mL of catalase
suspension to your table in
beaker.
• Use different seral pipettes to
dispense H2O2 and catalase
suspensions
• Total volume in test tubes will
be 7mL
• pH ranges tested will be 3,5,9
& 11. Change data tables to
reflect this alteration.
• Post and average the class data
Part 1 Protocol
• Clean and dry the large test tubes
• If you are doing part 1 (concentration) add (in
this order…
– 3mL water
– 1 to 4 mL of Catalase enzyme suspension
– 3mL H2O2
Immediately cap the tube and collect the data
Part 2 Protocol
• Clean and dry the large test tubes
• Place test tube into 0-5°C ice bath
• Add (in this order)…
– 3mL water
– 1 mL of Catalase enzyme suspension
– 3mL H2O2
Immediately cap the tube and collect the data
Repeat steps at room temperature, 30-35 °C and 50-55°C
Part 3 Protocol
• Clean and dry the large test tubes
• Add (in this order)…
– 3mL pH 3 solution
– 1 mL of Catalase enzyme suspension
– 3mL H2O2
Immediately cap the tube and collect the data
Repeat steps using 3mL of pH 5, 9 and 11