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 dataRepeat 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 dataRepeat steps using 3mL of pH 5, 9 and 11