MDG 15

Which statement about feedback inhibition is true?

• 1. It allows a cell to adapt quickly to fluctuations in the supply of a substance it needs.

• 1. It is typically found in anabolic (biosynthetic) pathways.

• 1. The end product of the metabolic pathway controls the activity of the first enzyme in the pathway.

• 1. If the end product accumulates in the cell, the whole pathway is shut down by inhibiting enzyme activity.

• 1. All of the choices are correct.

Both the trp operon and the lac operon experience negative control.

• True

• False

Both the trp operon and the lac operon experience positive control.

• True

• False

In general, operons that encode the enzymes of a biosynthetic (anabolic) pathway, such as the trp operon, are __________, and those encoding the enzymes of a catabolic pathway (such as the lac operon) are __________.

• 1. permanently on … permanently off

• 1. inducible … repressible

• 1. repressible … inducible

• 1. easily mutated … resistant to mutations

• 1. permanently off … permanently on

In an inducible operon, the inducer is often the __________ in the pathway being regulated; the inducer binds to the __________, thus rendering it __________.

• 1. end product … repressor … inactive

• 1. end product … corepressor … inactive

• 1. substrate … corepressor … inactive

• 1. substrate … repressor … active

• 1. substrate … repressor … inactive

A scientist clones a regulatory gene that is involved in controlling the expression of other genes, and discovers that the regulatory gene encodes a histone deacetylase enzyme. It is likely that this enzyme regulates gene expression by __________.

• 1. causing looser packing of the chromatin at the target gene, thereby inhibiting transcription

• 1. causing looser packing of the chromatin at the target gene, thereby enhancing transcription

• 1. causing tighter packing of the chromatin at the target gene, thereby inhibiting translation

• 1. causing tighter packing of the chromatin at the target gene, thereby enhancing transcription

• 1. causing tighter packing of the chromatin at the target gene, thereby inhibiting transcription