1. The clear protein of an egg white becomes opaque and firm when cooked. Using
ID: 52678 • Letter: 1
Question
1. The clear protein of an egg white becomes opaque and firm when cooked.
Using your knowledge of macromolecules explain what happened at a molecular level
2. Proteins have various functions within a cell. Describe the characteristics of protein structures that result in this diversity. Be specific.
3) Explain the purpose of the following materials for the protein separation lab:
a. SDS
b. DTT
c. Heat
4. What is “osmotic shock” and why it is used ?
5. Which arrow points to a peptide bond?
(fromhttp://www.biology.arizona.edu/biochemistry/problem_sets/large_molecules/01Q.html as of 11/17/08)
A. 1
B. 2
C. 2 and 3
D. 3
E. 4 and 5
Explanation / Answer
1. 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 chains are raveled up in a specifically arranged 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. As an egg cooks, the heat causes the bonds within the proteins to break, a process called denaturation.
As these proteins chains unfold and entangle with other proteins, new bonds form between these amino acids and the amino acids of neighboring proteins, causing the texture to change. At 62-65°C, the most heat sensitive protein in egg white, ovotransferrin, constituting 12% of the egg white, starts its denaturation and the egg white starts setting. At 80°C, the main protein ovalbumin (54% of the egg white) denatures. The denaturation and rearrangement at 80°C has caused the egg white to be firm. When the yolk is heated, the proteins
undergo heat denaturation and precipitate.
2.
Proteins are of utmost significance to biological systems. These are most critical to life and
perform various functions. Some of their roles are given below.
1. Many proteins act as catalysts, thus usually enhancing the rate of chemical reactions to such
extents as needed by the living cells.
2. The fibrous proteins serve as components of the tissues holding the skeletal elements together.
Collagen is a structural unit of connective tissues.
3. The nucleoproteins serve as carriers of genetic characters and hence govern inheritance of
traits.
4. Proteins also perform transport functions. Many compounds enter the cells and accumulate
inside at much higher concentrations than expected from diffusion alone. These changes require the
input of energy and are usually termed active transport. The mechanism of active transport involves
proteins either as catalysts or as adsorbents or as both.
5. Various protein hormones are known. These regulate the growth of plants and animals, besides
controlling many other physiological functions
3.
a. Sodium dodecyl sulphate(SDS) is an anionic detergent and it disrupts macromolecules(proteins) whose structure has been stabilized by hydrophobic interactions. SDS bands the hydrophobic regions of the proteins which separates them into their component subunits (polypeptides). SDS imparts a larger negative charge to the denatured polypeptides which overshadows the charge present on the polypeptides. Since al the polypeptides now have the similar charge they will get separated solely on the basis of their size.
b.Dithiothreitol (DTT) is a chemical used to reduce disulfide bond s quantitatively. As a reducing agent, it is used to reduce the disulfide bonds of proteins and peptides. It prevents intramolecular and intermolecular disulfide bonds from forming between cysteine residues of proteins. Dithiothreitol(DTT) reduces disulfides to dithiols, allowing release of the DNA from its protective proteins and further degradation of the proteins by Proteinase K.
c. heat usually denatures the proteins and reaks the bonds between them, which results in its precipitation and separation.
4. Osmotic shock or osmotic stress is a sudden change in the solute concentration around a cell, causing a rapid change in the movement of water across its cell membrane. Under conditions of high concentrations of either salts, substrates or any solute in the supernatant water is drawn out of the cells through osmosis. This also inhibits the transport of substrates and cofactors into the cell thus “shocking” the cell. Alternatively, at low concentrations of solutes, water enters the cell in large amounts, causing it to swell and either burst or undergo apoptosis.
5. E- 4 and 5
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