One primer attaches to the __ end of the gene region on the 5' to 3' strand, another to the ___ end of the gene region of the 3' to 5' strand. This was maybe not explicit in the video. 3’ and 5’ refer to the orientation of the DNA strand. The 3’ end is the end that has the OH group used for adding new nucleotides. The 5’ end is the end where a phosphate sticks out from the ribose. The two strands that make up the DNA molecule run anti parallel to each other. Synthesis is always in the 5’ to 3’ direction (because that is where new nucleotides attach), and the template strand is read 3’ to 5’ (because it runs antiparallel).