If a stimulus plus a response results in a satisfying outcome, the probability of that responds occurring again

Increases. When an outcome is good our recompense centre makes us feel well, good about it. We then associate such feelings to the response. Next time we receive such stimulus, we will likely respond in the same way so we can feel the same rewarding feelings. For example, if when I have a test (stimulus), I study (response), and then have a good grade (satisfying outcome), the probability of studying again when I have a test increases.

Dna strands are split apart to allow an opening for replication. the opening has two replication forks so synthesis goes toward them in 5' to 3' direction.