Although the expression of most genes is tightly regulated,some genes are expressed at roughly constant rates (i.e. ,constitutively).Which of the following genes would you predict to be constitutively expressed?
A)genes involved in the biosynthesis of the amino acid tryptophan
B)genes involved in the degradation of tryptophan
C)genes involved in the degradation of arabinose,a sugar
D)genes that code for ribosomal RNAs
E)genes involved in the transport of the sugar maltose

Question

Quizplus · Accepted Answer

Genes that code for ribosomal RNAs are essential for protein synthesis, which is necessary for cell growth and division. Therefore, it is advantageous for these genes to be constitutively expressed to ensure that the cell has a constant supply of ribosomes. Genes involved in biosynthesis or degradation of specific molecules may be regulated depending on the cell's needs, and genes involved in transport may also be regulated depending on the availability of the transported molecule. Therefore, choices A, B, and E are less likely to be constitutively expressed. Choice C may or may not be constitutively expressed depending on the organism's preferred energy source.

Although the Expression of Most Genes Is Tightly Regulated,some Genes