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Download 4. The diagram below shows a segment of DNA with a total length of
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1995 4. The diagram below shows a segment of DNA with a total length of 4,900 base pairs. The arrows indicate reaction sites for two restriction enzymes (enzyme X and enzyme Y). (A) Explain how the principles of gel electrophoresis allow for the separation of DNA fragments. (B) Describe the results you would expect from the electrophoretic separation of fragments from the following treatments of the DNA segment above. Assume that the digestions occurred under appropriate conditions and went to completion. I. II. III. IV. (C) DNA digested with only enzyme X DNA digested with only enzyme Y DNA digested with enzyme X and enzyme Y combined Undigested DNA Explain both of the following. (1) (2) The mechanism of action of restriction enzymes The different results you would expect if a mutation occurred at the recognition site for enzyme Y. END OF EXAMINATION Copyright © 1970 to 2004 by College Entrance Examination Board, Princeton, NJ. All rights reserved. For face-to-face teaching purposes, classroom teachers are permitted to reproduce the questions. Web or Mass distribution prohibited. DNA QUESTION 1985: L. PETERSON/AP BIOLOGY Describe the operon hypothesis and discuss how it explains the control of messenger RNA production and the regulation of protein synthesis in bacterial cells. STANDARDS: BACKGROUND: Max. = 2 points __ Definition of operon (functionally related genes whose expression is controlled) __ DNA consists of genes coding for both structural and regulating proteins (Hypothesis) __ Authors of Hypothesis DESCRIPTION OF OPERON (likely the Lac Operon): Max. = 8 points Structure (diagram) __ promoter site __ repressor site __ operator site __ structural genes __ inducer Max. 4 Function Max. 4 __ binds RNA polymerase* at 3' site on DNA (* also cAMP-CAP) __ produces repressor protein: stops RNA polymerase attaching to promoter __ site of attachment of repressor protein __ codes for sequential protein __ serves to inactivate repressor CONTROL OF mRNA PRODUCTION & CONSEQUENCES re PROTEIN SYNTHESIS: Max. = 5 __ Inducible model: derepression (lactose example) [gene always off] = 3 points __ Repressible model: corepression (tryptophan-histidine) [gene always on] = 3 points __ CAP model: catabolite induction: with decrease in glucose -> increase in cAMP cAMP-CAP binds to promoter site therefore, transcription -> lactose metabolism = 3 points (above require explanation & example) __ Adaptive significance = 2 points __ Final fate of mRNA transcribed = 2 points