Year 12 Biology OCR Planning Exercise

Introduction

In this investigation I am going to investigate the effect of calcium ions on the rate at which Rennin Coagulates milk. Rennin, is a protease, which coagulates milk, and is most commonly found in the stomachs of calves, however the rennin which I am going to be using is sourced from Fungi. The calcium ions in this investigation are the enzyme co-factor, which means that they help to form the enzyme-substrate complex by helping mould either the enzyme, or the substrate into a more suitable shape so that they may fit together easier. In this case, the substrate will be the milk protein, Casein.

Casein is a protein which makes up approximately 80% of milk proteins (http://www.sciencebyjones.com/milk_notes.htm), and is present in the milk in small, microscopic globules called Casein Micelles. These Micelles are a similar to standard micelles, in the fact that they are composed of proteins which have a hydrophilic head facing towards the outside, and a hydrophobic tail facing to the inside. These Casein Micelles are held together by calcium ions; therefore the more Calcium ions present in the solution, the greater the amount of micelles present and the stronger the force of attraction between them. The coagulation of the milk is where the Hydrophilic head is split from the hydrophobic tail; therefore they clump together in the solution, precipitating out in the form of flecks of milk protein.

As shown in the diagram overleaf, the casein micelle is made up of sub micelles, which are these hydrophobic and hydrophilic clusters, which contain calcium, which holds them together.

Structure of a micelle and sub micelle

(http://www.foodsci.uoguelph.ca/deicon/casein.html)

Safety

General lab rules must be followed at all times, so safety goggles must be worn at all times, no eating or drinking and any glass breakages must be reported then cleaned up.

Rennin

Rennin is an enzyme protease; therefore safety goggles must be worn to prevent any from going into the eyes. ...