The shape of the DNA molecule is called a double

The shape of the DNA molecule is called a double helix.

Idk if this is the answer you need but a double helix

Hope this helped srry if it didn't.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.