How to improve DNA extraction

Question

I am using the following protocol to extract chromosomal DNA from bananas:

1. Cut up one banana into small pieces, approximately (1 cm³)
2. Add ½ a cup of warm salt water and the banana pieces into the blender and set to max for 5-10 seconds
3. Poor into a beaker and add 1 teaspoon of detergent to the beaker
4. Stir for 5 mins with a spoon to break down the plasma membrane
5. Place the mixture into a centrifuge for 30 seconds
6. Pour the mixture through a gauze with a beaker catching the liquid underneath
7. Smoothly pour cold ethanol into the mixture at a 1:1 ratio so a clear layer of liquid will form on top of your mixture

Why is the centrifuge step (5) needed? Why would that increase the yield of DNA?

Answer 1

In a protocol like this, a low centrifugation is typically used to separate DNA in solution from larger, heavier components of the mixture. By lightly pelleting the banana slurry at the bottom of the tube, the DNA in solution is less likely to stick to that fraction of the mix when you pour it through the gauze. That's where your increased yield will come from.