When the new word is ready from the memory, it is latched into the MBR register by setting MBR-LD to 1, and then back to 0, as shown in step 4 and 5. In step 5 memory is "turned off" by setting MA back to 0.

Also in step 5, we add +1 to the binary number in the PC register by setting PC-INCR to 1. This causes the PC to point to the next memory address for its next fetch, thereby implementing sequential execution of a list of commands kept in memory. If the instruction that is yet to be executed is a jump, it will merely overwrite PC, so it doesn't hurt to add 1 to PC anyway. If that old value is completely overwritten by a jump instruction, so what.