Question

when substrate level phosphorylation occurs,
multiple choice
atp is converted into adp plus a phosphate group.
amp is converted into nadh by adding a phosphate group
nad⁺ is converted into nadh
adp is converted into atp by addition of a phosphate group.

Explanation:

1. Analyze the first option: Substrate - level phosphorylation is about ATP synthesis, not ATP breakdown. So "ATP is converted into ADP plus a phosphate group" is incorrect as it describes ATP hydrolysis.
2. Analyze the second option: AMP and NADH are different molecules with different functions and structures. AMP cannot be converted into NADH by adding a phosphate group, so this option is wrong.
3. Analyze the third option: The conversion of \(NAD^+\) to \(NADH\) is related to redox reactions (electron transfer), not substrate - level phosphorylation. Substrate - level phosphorylation is about ATP production from ADP and a phosphate group, so this option is incorrect.
4. Analyze the fourth option: Substrate - level phosphorylation is defined as the process where a phosphate group is transferred from a substrate molecule to ADP, resulting in the formation of ATP. So "ADP is converted into ATP by addition of a phosphate group" correctly describes substrate - level phosphorylation.

Answer:

D. ADP is converted into ATP by addition of a phosphate group. (Note: Assuming the last option is labeled D. If the original options had different labels, adjust the label accordingly based on the position of "ADP is converted into ATP by addition of a phosphate group" in the options list.)