Question

Why is the answer C? Is it because SAICAR/CAIR includes all the other intermediates, which helps ADE5? Please provide an explanation. Thanks.

ADE5 21. Review the partial diagram of arginine biosynthesis pathway. PRA, GAR, FGR, FGM, AIR, CAIR and SAICAR designate different intermediate compounds, while ADE5, ADES, ADE6, ADEZ, ADE2, and ADE1 designate enzymes encoded by different genes. Which of the following statements are true: GAR ADES FGAR ADE6 FGAM ADET AIR a. Growth of the ade5 mutant can be rescued by addition of PRA b. Growth of the ade1 mutant can be rescued by addition of CAIR or SAICAR c. Growth of the ade5 mutant can be rescued by addition of CAIR or SAICAR d. Growth of the ade1 mutant can be rescued by addition of PRA e. All of the above statements are true. ADE2 CAIR ADE1 SAICAR

Answer 1

True statements,

B. Growth of the ade1 mutant can be rescued by addition of CAIR or SAICAR.

C. Growth of the ade5 mutant can be rescued by addition of CAIR or SAICAR.

This is because the final product of the pathway is SAICAR. So, mutation of any intermediate enzyme or non-availability of intermediate products can be compensated by the availability of the final product.