Question

mutant n. crassa cells that cannot make arginine on their own must be supplied with arginine for arginine synthesis:
metabolic pathway
precursor
enzyme 1
ornithine
enzyme 2
citrulline
enzyme 3
arginine
16.1.
if a mutant lacked enzyme 2, would it still be able to grow if it were provided with (a) ornithine or (b) citrulline in its diet? see section
(a) yes; (b) yes
(a) no; (b) yes
(a) yes; (b) no
(a) no; (b) no

Explanation:

1. Understanding the Metabolic Pathway: The pathway is Precursor → (Enzyme 1) → Ornithine → (Enzyme 2) → Citrulline → (Enzyme 3) → Arginine. The mutant lacks Enzyme 2, so it can’t convert ornithine to citrulline on its own.
2. Analyzing Part (a) (Ornithine Supplied): If ornithine is provided, the mutant still can’t use it to make citrulline (because Enzyme 2 is missing). So it can’t produce arginine from ornithine, but wait—no, wait: Wait, the mutant needs arginine to grow. Wait, no—wait, the pathway is for arginine synthesis. The mutant can’t make arginine on its own. If we supply ornithine, but the mutant lacks Enzyme 2 (to turn ornithine into citrulline), then it can’t proceed to make arginine from ornithine. Wait, no—wait, maybe I got it wrong. Wait, the question is: “would it still be able to grow if it were provided with (a) ornithine or (b) citrulline”. Wait, the mutant lacks Enzyme 2. So:

• For (a) Ornithine: The mutant needs to convert ornithine → citrulline (Enzyme 2) → then citrulline → arginine (Enzyme 3). But Enzyme 2 is missing, so it can’t turn ornithine into citrulline. So even with ornithine, it can’t make arginine. Wait, no—wait, maybe the mutant can’t make ornithine on its own, but if we supply ornithine, does it need Enzyme 2 to use ornithine to make arginine? Yes. So without Enzyme 2, ornithine can’t be converted to citrulline, so no arginine. So (a) No.
• For (b) Citrulline: If we supply citrulline, the mutant can use Enzyme 3 (which it presumably has, since the mutation is only in Enzyme 2) to convert citrulline to arginine. So with citrulline, it can make arginine and grow. So (b) Yes.

Wait, but the options: Let's check the options. The options are:

• (a) Yes; (b) Yes
• (a) No; (b) Yes
• (a) Yes; (b) No
• (a) No; (b) No

So the correct one is (a) No; (b) Yes, which is the second option (the one labeled (a) No; (b) Yes). Wait, looking at the image, the options are:
First option: (a) Yes; (b) Yes
Second: (a) No; (b) Yes
Third: (a) Yes; (b) No
Fourth: (a) No; (b) No
So the correct answer is the second option: (a) No; (b) Yes.

Answer:

(a) No; (b) Yes (the second option, e.g., the option with " (a) No; (b) Yes " text)