Unformatted text preview: llosteric or noncompetitive inhibitor. o Binding of allosteric activator. o Feedback control. o pH or temperature changes. o Cleavage of pre-enzyme (e.g., zymogen). o Cooperativity; coenzymes; cofactors. o Covalent modification (e.g., phosphorylation). • Competitive inhibitors binding in the active site prevent substrate binding. NOTE: The active site regulating enzyme activity is not enough to earn a point. © 2008 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP® BIOLOGY 2008 SCORING GUIDELINES
Question 1 (continued)
Cell signaling (2 points maximum) • Receptor-ligand binding (1 point for each bullet) o Event: Ligand binds specifically to receptor. o Result: Receptor structure altered by binding, transducing signal through membrane. Examples may include hormones, neurotransmitters. • Enzyme-linked receptors: binding of ligand causes enzyme to catalyze reaction. • Gap junctions: shape of junctions allows for passage of regulatory ions or molecules. • Ligand-gated channel: binding of ligand opens channel. • Immune signaling: leads to activation of cells. (c) Abnormal hemoglobin is the identifying characteristic of sickle cell anemia. Explain the genetic basis of the abnormal hemoglobin. Explain why the sickle cell allele is selected for in certain areas of the world. (3 points maximum) Genetic basis (2 points maximum) • Point mutation in DNA; base substitution leading to a different amino acid in the hemoglobin...
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