SAT Subject Biology Practice Question 466: Answer and Explanation
16. β-galactosidase (β-gal) is a bacterial enzyme used in the metabolism of lactose. Three different groups of human intestinal bacteria were cultured in a glucose-based medium. At Time 1, the bacteria were transferred to media containing lactose as a nutrient source instead of glucose. At Time 2, the bacteria were returned to the glucose-based medium. Samples of bacteria were removed at five-minute intervals and tested for the presence of β-gal. The results are presented below.
Which of the following could be reasons for the inability of Group 3 to produce β-gal?
I. Error in DNA replication
II. Error in RNA transcription
III. Error in protein translation
A. I only
B. III only
C. I and II only
D. II and III only
E. I, II, and III
Correct Answer: E
E An error in any of these processes could result in a nonfunctional protein. Option I, an error in DNA replication, could cause a mutation in the β-gal gene, leading to defective mRNA and a defective protein. Option II, an error in RNA transcription, could produce a defective mRNA, resulting in a defective protein. Option III, an error in protein synthesis, could definitely produce a defective protein. Remember the I, II, III technique.