Which of the following are CORRECT about protein structure?

1. Secondary structure is formed by a repeating pattern of interactions among the polypeptide backbone atoms
2. Tertiary structure is the three-dimensional arrangement of the polypeptide backbone atoms only
3. Quaternary structure refers to an assembly of multiple polypeptide subunits

1. $\text{P}$ and $\text{Q}$ Only
2. $\text{P}$ and $\text{R}$ Only
3. $\text{Q}$ and $\text{R}$ Only
4. $\text{P, Q}$ and $\text{R}$