Answer: The part of DNA that the teacher was modelling would be the backbone of DNA.
Step-by-step explanation:
The DNA is made of double helical structure which is twisted. In the structure of DNA two strands are coiled among each other.
The DNA consists of the nitrogenous bases, phosphate groups and deoxy-ribose sugar.
The backbone of DNA is made up of sugar( alternating )and phosphate group.The nitrogenous bases such as adenine, cytosine ,guanine and thymine are joined to the deoxy-ribose sugar.
This backbone part was part that the teacher was making as a model by using two coiled springs.