"Excellent. Answered all those questions I had that are never covered in text books, such as how big is a piece of DNA?"
Beta cells are specialised to produce insulin. They have a well-developed rough endoplasmic reticulum, to produce the protein hormone. This is then stored in cytoplasmic vesicles before it is secreted. The process requires energy and beta cells contain many mitochondria to provide ATP.
Roll over the image to see the parts of the cell involved in insulin production.
Insulin is a protein and there are several stages in its production. The animation shows the process of protein synthesis. When insulin is being produced, it is the insulin gene in the nucleus that is transcribed into messenger RNA.