We rarely use "articles" in laws except in the Constitution itself. If you look at the back of the MPEP, you would find that there are appendix pages listed as follows:
Ap. L means Law. These are under title 35 of the United States Code. It was written by Congress and modified by Congress every 50-60 years. For patent bar purpose, you pretty much need to know 35 USC 101, 102, 103, and 112 by heart. There are about 10% questions in law.
Ap. R means rules. These are under title 37 of the code of federal regulations. These are written and published by the government. For patent bar, you need to be familiar with chap 1, as 99% questions will be from this chapter.
Then you also need to know the MPEP, the procedures written by the PTO for its operation. You need to read through chapter 2100 three times. Skim chap 1800 as there are increasing numbers of questions in PCT. Be familiar with chapter 600 and 700 as well.
