Biology (11th Edition)

Published by McGraw-Hill Education
ISBN 10: 1-25918-813-2
ISBN 13: 978-1-25918-813-8

Chapter 16 - Control of Gene Expression - Review Questions - Synthesize: 2


The lac operon is negatively regulated because the lac repressor binds when lactose is absent, and no gene expression then occurs. The genes are turned off (negative/off). In contrast, the trp operon is turned on in the absence of tryptophan (positive/on).

Work Step by Step

The key here is see that negative regulation involves the turning off of genes by a regulatory protein when their expression is not needed while positive regulation involves turning on by a protein when expression of those genes is needed.
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