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🧬AP Biology
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🧬AP Biology

FRQ 4 – Conceptual Analysis (Short)
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Unit 1: Chemistry of Life
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Practice FRQ 1 of 171/17

4. The stability of biological macromolecules is essential for life and is influenced by environmental factors such as temperature. Thermus aquaticus is a thermophilic bacterium found in hot springs where water temperatures can exceed 70°C. In contrast, Escherichia coli is a mesophilic bacterium that thrives in the human intestine at approximately 37°C. The DNA of these organisms must remain stable and functional at their respective environmental temperatures to ensure survival.

The double-helix structure of DNA is maintained by interactions between the nitrogenous bases on opposite strands. The specific pairing of bases ensures the fidelity of genetic information, while the strength of the interactions between strands determines the molecule's stability against thermal denaturation (melting).

A.

Describe the type of chemical bond responsible for holding the two strands of a DNA molecule together.

B.

Explain how the number of hydrogen bonds between specific base pairs contributes to the difference in stability between a DNA segment rich in Guanine-Cytosine (G-C) pairs and a DNA segment rich in Adenine-Thymine (A-T) pairs.

Scientists engineered a mutant strain of Thermus aquaticus by altering a gene essential for cell division. The original gene sequence contained a high proportion of Guanine-Cytosine (G-C) base pairs. In the mutant strain, mutations were introduced that replaced a significant number of G-C pairs with Adenine-Thymine (A-T) pairs. The scientists then attempted to culture the mutant bacteria at 75°C.

C.

Predict the likely effect of the increased A-T content on the survival of the mutant Thermus aquaticus strain at 75°C compared to the wild-type strain.

D.

Justify your prediction in part C.

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Free Response Question Practice

This practice environment simulates the AP AP Biology Free Response Questions section. Here are some guidelines:

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