Imm o.l Part II. Short answers. Indicate what 1. Describe at least three factors
ID: 695632 • Letter: I
Question
Imm o.l Part II. Short answers. Indicate what 1. Describe at least three factors responsible for denaturation of proteins. type of interactions is (are) affected by each factor. ( 2. Although both starch and cellulose are polyglucose, the two materials are very different in their physical interaction with water. Describe the difference and explain the reason for the difference. (4 points) 3. What is the difference between amphipathic and non-amphipathic lipids? Give an example of each. (4 points)
Explanation / Answer
Q.1 Describe at least 3 factors responsible for denaturation of proteins? Indicate what type of interactions is /are affected by each factor?
The main forces that affect structure are electrostatic forces, hydrogen bonding forces, hydrophobic forces, and disulfide bonds. Each of these affect protein structure in different ways.The factors that contribute the denature of proteins are
1. Changes in temperature:
Heat can be used to disrupt hydrogen bonds and non-polar hydrophobic interactions. This is because heat increases the kinetic energy and causes the molecules to vibrate rapidly and violently that the bonds are disrupted. Example: The proteins in eggs denature and coagulate during cooking.
2. Changes in pH :
Most proteins at physiological pH are above their iso-electric points and have a net negative charge. When the pH is adjusted to the isoelectric point of the protein, its net charge will be zero. Charge repulsions of similar molecules will be at minimum and many proteins will precipitate.
The isoelectric point is the pH at which a particular molecule carries no net electrical charge in the statistical mean. Because a majority of weakly acid remains in nearly every protein, they are generally negatively charged at neutral pH. The isoelectric point is significant in protein purification because it represents the pH where solubility is typically minimal.
3. Changes in salt concentration :
The changes in salt concentration affect the denaturation of proteins due to the forces like electrostatic forces and hydrogen bonding.
Q.2 Both Starch and cellulose are polyglucose, the two materials are different in their interaction with water. Describe the difference and explain the reason for their difference
Starch and cellulose molecules are polysaccharides. Starch and cellulose are constructed of glucose units joined together by acetal linkages. They are different due solely to the type, number and location of the linkages. The structure formed when the molecules share oxygen is determined by which form of glucose is linked together. Starch contains alpha glucose, while cellulose is made of beta glucose. This difference may seem minor, but it plays a big role in the 3-D shape of the molecule.
Although both starch and cellulose are polymeric forms of glucose, they differ in their chemical and physical properties. These differences are mainly attributed to the difference in linkage.
(a)Structure
Cellulose is mostly linear chains of glucose molecules linked together by beta 1,4 glycosidic bonds whereas starch is found in both linear and branched chains.
The orientation of the glycosidic linkages in cellulose makes the glucose rings to be arranged in a flip flop fashion which contributes to the rigidity. There are no branching chains in cellulose. Cellulose also owes its rigidity to the numerous hydrogen bonds in the structure which in turn makes a good structural polysaccharide.
(b)Chemical bond
Cellulose has beta 1,4 linkage between the glucose units while starch has alpha 1,4 linkages. Cellulose occurs in nature as pure cellulose , hemicellulose or lignin. Starch occur in two forms- amylase and amylopectin. Amylose is simple linear form where as amylopectin is complex and branched. Glycogen is the storage form of starch in animals and more branched than amylopectin.
(c)Function
Cellulose is a structural polysaccharide. Starch is mainly a storage polysaccharide.
(d)Hydrolysis
Cellulose on hydrolysis form cellobiose and ultimately to glucose monomers by the action of celulases. These enzymes are less common and found in certain protozoa and bacteria in small quantities. Starch is acted upon by amylases which break it into glucose units.
(e)Digestibility
Starch can be broken down to maltose and then finally to glucose by the enzymes present in humans. Cellulose cannot be digested properly in the absence of the cellulase enzymes.
Although starch and cellulose are both polymeric forms of glucose, they differ in the properties. These differences tend to be the result of the difference of a single chemical bond between the monomeric units. The varied nature makes the carbohydrates to play both energy providing function as well as structural roles.
Q3. What is the difference between amphiphatic and non- amphiphatic lipids? Give an example of each?
An amphiphile is a chemical compound possessing both hydrophilic (water-loving, polar) and lipophilic (fat-loving) properties. Such a compound is called amphiphilic or amphipathic. All of the lipid molecules in cell membranes are amphipathic (or amphiphilic)—that is, they have a hydrophilic (“water-loving”) or polar end and a hydrophobic (“water-fearing”) or nonpolar end. The most abundant membrane lipids are the phospholipids. These have a polar head group and two hydrophobic hydrocarbon tails.
Examples of amphiphilic compounds are phospholipids, cholesterol, glycolipids, fatty acids, bile acids.
Non Amphiphilic molecules normally have a rigid structure which doesn’t have both polar and non polar nature .
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