As I know, not only in 5G, also in LTE the TPC command is required for SRS transmission.
The sequence is :
TPC control a transmit power of its PUSCH,SRS or PUCCH transmissions.
In power control the closed loop depends on eNodeB providing feedback to the UE in the form of Transmit Power Control (TPC) commands & TPC commands are signaled to the UE via Downlink Control Information (DCI) formats.
example: DCI format 3 & 3A.
Similarly in 5G NR,
DCI Format 2_2 is used for the transmission of TPC commands for PUCCH, PUSCH & Format 2_3 used for SRS transmission.
