EXPERIMENT 5: DENATURATION OF EGG WHITE PROTEIN
Introduction: Denaturation is a process in which proteins which proteins or nucleic acids lose acids lose the quaternary structure,, tertiary structure and structure structure and secondary structure which structure which is present in their native state, state, by application of some external stress or compound such as a strong acid acid or or base base,, a concentrated inorganic salt, inorganic salt, an organic organic solvent solvent (e.g., alcohol or chloroform chloroform), ), radiation or heat heat.. rotein is large molecules made up of small amino acids. rotein folding is !eys to whether a globular protein or a membrane protein can do its "ob correctly. correctly. It must be folded into the the right shape to function. #ut hydrogen bonds, which play a big part in folding, are rather wea!, and it does not ta!e much heat, acidity, or other stress to brea! some and form others, denaturing the protein. $he shape of a protein is associated with food processing properties, such as solubility, gel formation, and en%yme activity. a ctivity. In the egg whites the albumin will change from clear to white. &e will explore how the following denature egg albumin by heat that done by coo!ing, acids and bases (can form ions side groups of amino acids), by organic compound and also by heavy metal (react with disulphide bonds).
Objective:
$o study the different effect of denaturation of protein found in the white albumin.
Materials / Aarat!s:
'aw eggs * +odium chloride (a-l) * sodium bicarbonate (a-/ 0) * +ilver nitrate (1g/ 0) 2inegar $est tube +patula $ong ot plate or #unsen burner +tirring rod or 3lass rod.
Pr"ce#!re:
. 1 0 ml of water was place in a bea!er 4ml and heat to boiling. 5. $he test tube was label from until 6. 0. $he raw egg was separated and placed the egg white in a test tube until half filled. 4. 6. 7. 8. 9. .
$he egg yol! was discards. $he test tube number in the boiling water and allow coo!ing till egg turns white. $he 6 ml of * of sodium chloride was put to test tube number 5 and stir. $he 6 ml of * of sodium bicarbonate was put to test tube number 0 and stir. $he 6 ml of vinegar was put to the test tube number 4 and stir. $he 6 ml of * 1g/ 0 was put to the test tube number 6 and stir. $he observation was recorded in the table below.
Res!lts: Table 5$%: De&at!rati"& "' E(( W)ite Pr"tei&$ Test t!be
Treat*e&t
Observati"&
eat
&hite solid formed.
5
a-l ; ionic compound
-lear colour and have very little white precipitate.
0
a-/0 ; base
4
2inegar ; acid
1 lot of white precipitate
6
1g/0 = heavy metal
&hite precipitate layer on the top.
Disc!ssi"&:
In this experiment, we need to study the different effect of denaturation protein that found in white egg albumin. $he function principle tells that changing the structure of a protein will
affect its function. /ften that means that function is lost. Denaturation of a protein means loss of the protein function due to the structural change in the protein caused by some chemical physical factor such as high temperature that may cause the folded protein to unfold, to unravel. &hen the albumin was heat until it become white solid it will disrupt hydrogen bonds and non;polar hydrophobic interactions. 1s results, after heat the albumin change colour from colourless to white solid formed. $his occurs because heat increases the !inetic energy and violently that the bonds are disrupted. $he protein in eggs denatured and coagulated during coo!ing. /ther foods are coo!ed to denature the proteins to ma!e it easier for en%ymes to digest them. >edical supplies and instruments are sterili%ed by heating to denature proteins in bacteria and thus destroy the bacteria. $he denaturation of egg white protein is due to the addition strong acids or bases affect the groups that compose the protein, changing the net charge. $hese changes or the absence of one or more charge can affect the protein folding by repulsion of charges and the hydrophobic interactions, causing denaturation. In most experiments, strong acids and bases that are used are usually sodium chloride respectively. ydrophobic bonds in globular protein bac!bones can also be bro!en by organic solvent. +alt such as a-l allow the protein to salt out which causes precipitation by the binding of the salt ions to the charged side chains. eavy metal act to denature protein in much the same manner as acids and bases. eavy metal salt usually contain 1g?, -d?, b? and other metals with high atomic weights. +ince, salts are ionic they disrupt salt brides in proteins. $he reaction of a heavy metal salt with a protein usually leads to an insoluble metal protein salt. $his reaction is used for its disinfectant properties in external applications. @or example, 1g/0 is used to prevent gonorrhoea infections in the eyes of new born infants. eavy metals may also disrupt disulphide bonds because of their high affinity and attraction for sulphur and will also lead to the denaturation of protein.
+"&cl!si"&:
$here are a lot of factor that can affect the denaturation of egg white albumin. @or example heat, addition of strong acids and bases, exposure to organic solvents and also addition of
heavy metal. rotection of proteins against denaturation is one result of the buffering of biological solutions such as blood and the aqueous interior of living cells. If blood would h changed much from its normal value, proteins in the blood would begin to puc!er, buc!le, twist into different shapes, and unravel, with potential loss of function.
,!esti"&s:
) &hich method appeared to have the most dramatic denaturing effect on egg albuminA &hy do you thin! this method had a greater affectA $he heat is the most dramatic denaturing effect on egg albumin because it denatures the protein and changes the conformational shape of the protein and the bonds that maintain it shape. 5) /f the methods you tested, which would be more li!ely be used in food industryA In the food industry they most li!ely to use the method of heat as well, in fact, boiling an egg is already a favourite of many when it comes to different coo!ing method because the application of heat is safe for the food industry.
Re'ere&ces:
. 1dler, issen B, 86. Cn%ymic hydrolysis of protein for increased solubility. Bournal of 1gricultural and @ood chemistry. 54(7).;0. 5. http:dx.doi.org.7"."fca.54.9.8. 0. Dyer, B.>, lowman, -lerens,+,. 5. roteomic evaluation and location of E2#; induced photo of egg albumin. 5. 58(7).;. 4.
