While the food is in the stomach, it is mixed with acid, and enzymes, so chemical digestion takes place. During this, the peristaltic movements on the muscles in the wall of the stomach will mix the food until it is almost a fluid while is called chyme. After some, time the circular muscle between the stomach and the small intestine called pyloric sphincter opens briefly and a small amount of acid chyme is allowed into the duodenum.
The wall of the stomach is made of protein, and pepsin works on proteins in order to avoid self-digestion of the stomach wall, pepsin is released as an inactive form (Pepsinosion), which is activated by the acidic environment that’s why stomach secretes HCL
In this experiment, we are investigating the action of the enzyme pepsin on the egg white (the protein). We know that enzymes are proteins that catalyze a reaction by lowering the activation energy. The substrate used in this experiment consists of the egg white(albumen).It has been heated in order to solidify it, thus denaturizing it ,permanently damaging its protein structure and it has also been finally divided and suspended in water to form an opaque white liquid. The enzyme pepsin is from a mammalian digestive system. Depending on the conditions in the surrounding medium, it may break down (digest) the egg white to different extents, thus clearing the liquid.
All proteins, including those in egg white, are made of long chains of amino acids, which are similar to beads on a string. In a raw egg, these strings are raveled up in a tangled compact mass. Chemical bonds and interactions between the amino acids within each protein hold this mass in a specific shape and stop it from unraveling. Heat causes the bonds within the proteins to break, a process called denaturation. As these proteins strings unfold and entangle with other proteins, new bonds form between these amino acids and the amino acids of neighboring proteins, causing the texture change (change the structure.) and that is what happened in test tube (4). (Source: www.yahoo.com)
The optimum PH for pepsin is 2-3, so it is activated only in an acidic environment that s why pepsin has been activated only in test tube (3) that contains HCL+Pepsin (the length of egg white in the tube decreased which mean that it is digested.)
While in the other tubes the lengths of the egg white does not change, because:
1. Test tube (1) does not contain an enzyme, it contains (HCL+Water only) so no reaction will occur.
2. Test tube (2) contains pepsin, but without the acid HCL, that causes the decrease in PH to become 2-3 that is the optimum for pepsin.
3. Test tube (4) contains HCL+Water+boiled Pepsin, which means that the pepsin is denaturized.
4. Test tube (5) contains only water that does not affect proteins.
Sources of error:
In the instruction sheet, it is written that we must leave the test in the boiling water for 30min, but we did not because we hadn’t enough time. In addition, we were inaccurate in measuring the lengths of egg white.
We must leave the test in the boiling water for 30 min, and measure the lengths of egg white more accurate.