biology lab quiz 11/5

What is the primary function of enzymes?

Speed up chemical reactions by lowering activation energy.

How do enzymes lower activation energy?

They reduce the energy required for the transition from substrate to product.

Do enzymes cause reactions that would not otherwise occur?

No. They speed up reactions that can already occur.

What is catalase?

An abundant enzyme associated with cellular antioxidant pathways.

What toxic compound does catalase break down?

Hydrogen peroxide (H₂O₂).

What are the products of the catalase reaction?

Water (H₂O) and molecular oxygen (O₂).

What is the balanced catalase reaction?

2 H₂O₂ → 2 H₂O + O₂

Where is catalase found in eukaryotic cells?

Peroxisomes.

What is the role of superoxide dismutase (SOD)?

Converts reactive oxygen into hydrogen peroxide.

Why must cells eliminate hydrogen peroxide?

To protect cellular membranes and DNA from damage.

How many subunits does catalase have?

Four subunits, each with its own active site.

How can catalase reaction rate be measured?

By measuring oxygen gas production over time.

What is enzyme kinetics?

The study of the rate at which an enzyme catalyzes a reaction.

What happens when an enzyme binds its substrate?

It undergoes a physical change that modifies the substrate into product.

What happens to an enzyme after releasing its product?

It remains unchanged and can be reused.

Which molecule is altered during an enzyme reaction?

The substrate molecule; the enzyme is unchanged.

What yeast species was used in the catalase assay?

Saccharomyces cerevisiae.

What was the yeast solution concentration?

10% yeast solution.

What was the hydrogen peroxide concentration?

1% H₂O₂.

What was the control assay mixture?

10 mL yeast + 120 mL DI water + 20 mL H₂O₂.

What was the purpose of gently swirling the reaction flask?

To continuously agitate the reaction mixture.

How frequently was the meniscus recorded?

Every 15 seconds.

How many data points were collected before stopping the reaction?

6–10 data points.

What did the inverted graduated cylinder measure?

Oxygen gas production through water displacement.

What happens to the water level as oxygen accumulates?

Water is displaced as oxygen enters the graduated cylinder.

What two variables were changed in the enzyme kinetics experiments?

Enzyme concentration and substrate concentration.

What was varied in Experiment 1?

Yeast volume (catalase enzyme concentration).

What was varied in Experiment 2?

Hydrogen peroxide volume (substrate concentration).

In the catalase assay, what represents the enzyme?

Catalase in the yeast slurry.

In the catalase assay, what represents the substrate?

Hydrogen peroxide (H₂O₂).

What is the independent variable in an enzyme concentration experiment?

Enzyme concentration.

What is the independent variable in a substrate concentration experiment?

Substrate concentration.

What is the dependent variable in the enzyme kinetics graph?

Reaction velocity (V₀) of oxygen gas production.

How is water displacement calculated?

Current meniscus level − initial meniscus level.

What conversion factor converts displaced gas volume to mmol O₂?

22.4 mL gas = 1 mmol O₂ at STP.

How many milliliters are in one liter?

1,000 mL.

How many moles are in one millimole?

0.001 mole.

How do you calculate mmol O₂ produced?

mL water displaced ÷ 22.4 mL/mmol.

What does the first oxygen production graph show?

Millimoles of O₂ produced versus time.

Which section of the oxygen production curve determines initial velocity?

The steepest part of the curve.

How is initial velocity (V₀) determined?

Find the slope of the best-fit line using the steepest data points.

Why use only the steepest data points for V₀?

To estimate the initial reaction rate.

What does the slope of the best-fit line represent?

The rate of oxygen gas production over time.

What is the purpose of using class data?

To compare conditions and develop a model of enzyme kinetics.

What should be graphed against enzyme or substrate concentration?

Reaction velocity (V₀).

What does the enzyme kinetics model help identify?

Trends between enzyme/substrate concentration and reaction velocity.

What might affect catalase function besides substrate concentration?

Factors affecting protein structure and enzyme function.

What happens to the reaction if no yeast is added?

The 0 mL yeast condition serves as a comparison with no added enzyme source.

What happens to the reaction if no H₂O₂ is added?

The 0 mL H₂O₂ condition has no added substrate.

What is the role of the best-fit line in data analysis?

It provides a slope used to determine reaction velocity.

What additional effect might extra SOD have in Down syndrome?

It may increase hydrogen peroxide production, potentially increasing oxidative stress if not adequately removed by catalase.

What are the monomers of proteins?

Amino acids.

What determines a protein's function?

Its shape.

What can happen when a protein's shape is altered?

It may stop functioning or function incorrectly.

What is denaturation?

A change in a protein's shape that can affect its function.

What are antibodies?

Proteins involved in recognizing pathogens as part of the immune system.

What are receptors?

Proteins that bind signaling molecules and help cells respond to their environment.

What are transport proteins?

Proteins that move materials, usually across membranes.

What are structural proteins?

Proteins that maintain cell shape and can help with cellular movement.

What are enzymes?

Proteins that catalyze chemical reactions.

How does sickle cell anemia relate to protein structure?

A genetic mutation changing one amino acid alters hemoglobin structure.

Which amino acid substitution is mentioned in the sickle cell anemia example?

Glutamate is changed to valine.

What is an enzyme?

A special class of proteins that catalyze chemical reactions.

What is the role of enzymes in cells?

They help cells gain energy and build molecules.

What is a biological catalyst?

A substance that speeds up chemical reactions without being changed itself.

How do enzymes convert substrates into products?

They bind substrate molecules and help speed up their conversion into products.

What are the major properties of enzymes?

Increase reaction rates, act on substrates, remain unchanged, and can be reused.

Are enzymes changed during chemical reactions?

No. They remain unchanged and can be reused.

What environmental factors affect enzyme activity?

pH, temperature, and salt concentration.

What are cofactors?

Substances that some enzymes require assistance from.

What are enzyme inhibitors?

Ions or molecules that inhibit enzyme activity.

How is enzyme activity regulated in cells?

Enzyme activity is usually heavily regulated.

What determines enzyme-substrate specificity?

The shape of the active site and its ability to form weak hydrogen bonds.

What is an active site?

The region of an enzyme where the substrate binds.

What does enzyme kinetics describe?

How an enzyme functions relative to the amount of substrate available.

What limits the overall rate of enzyme activity?

The number of active sites available to bind substrate.

What is Vmax?

The maximum reaction rate when available active sites limit enzyme activity.

What does Km represent in the lecture?

The substrate concentration associated with half of Vmax.

What is the relationship between Km and Vmax?

Km is defined as ½ Vmax in the lecture's description.

What does Km describe?

The extent to which reaction rate depends on substrate concentration.

Where is catalase commonly found?

In all living things exposed to oxygen.

Which organism is used as the catalase source in the lab?

Yeast (Saccharomyces cerevisiae).

How does catalase protect cells?

It protects cells from oxidative damage.

How many H₂O₂ molecules can one catalase molecule convert per second?

Millions of H₂O₂ molecules per second.

What is the catalase reaction?

2 H₂O₂ → 2 H₂O + O₂.

Where does the catalase reaction occur in eukaryotic cells?

Peroxisomes.

What is the research question of the catalase experiment?

How do substrate and enzyme concentrations affect enzyme reaction rate?

What is varied in Experiment 1?

Enzyme concentration, by changing yeast volume.

What is varied in Experiment 2?

Substrate concentration, by changing hydrogen peroxide volume.

How many trials are performed for each experiment?

Three trials per experiment.

How many total trials are performed, including the control?

Seven total trials: one control and three trials for each experiment.

What is the main purpose of Part 2 of the spectrophotometry lab?

To determine the concentration of an unknown solution using a standard curve.

What is a standard curve?

A graph created using solutions of known dilution ratios and their average absorbance values.

What type of dilution scheme is used in Part A?

A 1:3 serial dilution.

How many dilution tubes does each team member prepare?

Three tubes: 1:3, 1:9, and 1:27.

What is the final volume required for each dilution tube?

3 mL.

What should the blank cuvette contain?

The handout asks this question but does not specify the answer.

When should the stock solution absorbance be measured?

Before starting the dilution scheme.

Why must the stock tube absorbance be measured before making dilutions?

The handout instructs this order but does not explain why.

What are the three dilution labels used for the standard curve?

1:3, 1:9, and 1:27.