AP Biology Unit 1.7 FRQ

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The stems and fruits of pineapple plants contain a group of protein-digesting enzymes collectively called bromelain and often used as an antibrowning agent for fruits and vegetables. Fruits and vegetables brown when they are bruised during transport or sliced and exposed to air. This browning is controlled by enzymatic pathways that produce brown pigments. The browning of fruits and vegetables reduces the nutritional value of the food, so antibrowning agents such as bromelain are used.

(a) Identify the type of monomer of which this enzyme is composed.

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Bromelain is a protein-digesting enzyme, and all enzymes are proteins. Proteins are composed of amino acid monomers.

Model Answer: Bromelain is composed of amino acid monomers, as it is a protein enzyme.

Scoring Criteria:

The response must indicate that amino acids are the monomers of which this enzyme is composed.

Keywords to look for: amino acid, amino acids

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(b) Bromelain works by breaking the enzymes that cause browning into smaller molecules. Explain how the reaction that breaks up the enzymes occurs.

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Bromelain catalyzes hydrolysis reactions, breaking peptide bonds in proteins by adding water molecules.

Model Answer: Bromelain catalyzes hydrolysis reactions, where water molecules are added to break the peptide bonds between amino acids in the browning enzymes, resulting in smaller peptide fragments or individual amino acids.

Scoring Criteria:

The response must indicate that bromelain enables hydrolysis of proteins, breaking peptide bonds by using water.

Keywords to look for: hydrolysis, peptide bond, water, break apart

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(c) The pH of a solution determines the charge of certain R groups. The pH of pineapple fruit ranges from 3.5 to 5.2. Predict the effect on the activity of bromelain if it is used in a product with a pH of 11.

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Enzymes have optimal pH ranges. Bromelain functions best in acidic conditions similar to pineapple fruit. A pH of 11 is highly basic and would likely denature the enzyme.

Model Answer: The activity of bromelain would decrease significantly or stop completely at pH 11 because the enzyme would likely denature due to the extreme deviation from its optimal acidic pH range.

Scoring Criteria:

The response must indicate that the activity of bromelain will decrease.

Keywords to look for: decrease, less active, denature, stop, slow down

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(d) Provide reasoning to justify your prediction.

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Extreme pH changes alter the enzyme's tertiary structure by disrupting hydrogen bonds and ionic interactions, changing the active site shape.

Model Answer: Enzymes have specific three-dimensional structures maintained by hydrogen bonds and ionic interactions. Extreme pH changes alter the charges on R groups, disrupting these bonds and causing the enzyme to denature. This changes the shape of the active site, preventing substrate binding and reducing catalytic activity.

Scoring Criteria:

The response must indicate that changes in pH affect interactions between amino acid R-groups, changing enzyme folding, shape, and function.

Keywords to look for: R-group, folding, shape, denature, active site, structure, charge

Score:

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