21. DNA is methylated at
A. AC sequences
B. TATA sequences
C. CAAT sequences
D. CG sequences
22. Why are several structural genes regulated as a unit in bacteria?
A. An accident of evolution
B. It allows coordinating regulation of genes with a common function
C. The bacteria chromosome is so small; many different genes must be controlled by the same promoter
D. none of the above
23. Alternate splicing of RNA transcripts is a mechanism to regulate
A. tubulin
B. tachykinins
C. DNA methylation
D. leucine zippers