What cause the banana to ripe?

Bananas ripen from green to yellow-green to yellow to slightly freckled to deeply freckled to bruised to black to rotten. A process called oxidation, starts. and it basically lets ethylene out of the fruit. The more ethylene that a fruit releases the more it ripens. The ethylene produces a gas called amylase which breaks down the starch in the bananas (starch is hard), and turns it into sugar, ( makes it soft.). Amylase then makes an enzyme that is called pectinase, which breaks down the cell walls of the banana (making it softer).