4 Marks Questions

Question 14 Marks

Define the following with an example of each:
(a) Polysaccharides
(b) Denatured protein

Answer

(a) Polysaccharides : Polysaccharides are formed by the polymerization of monosaccharides. Thus these are neutral polymeric compounds in which a large number of monosaccharide units are joined by glycosidic linkage in a long linear or branched structure. They are, naturally occurring, colourless, tasteless (not sweet), amorphous powders. They have the general formula $\left( C _6 H _{10} O _5\right)_n$. Some important polysaccharides are :
Cellulose, starch, glycogen, gums and pectin.
(b) Denaturation of Proteins : A protein found in a biological system having a unique 3D structure and specific biological activity is called a native protein. Various changes in the structure of protein such as pH , temperature, pressure, presence of salts or certain chemical agents can disrupt the complex three dimensional structure of the proteins. Disruption of the native structure (conformation) of a protein is called denaturation. Due to denaturation a protein loses its biological activity.

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Question 24 Marks

What are amino acids?

Answer

Amino acids are the building blocks of the molecular structure of the important and very complex class of bio-molecules known as proteins. The proteins on hydrolysis gives mixtures of the component amino acids.
As the name suggests, amino acids are bifunctional compounds containing both amino $\left( NH _2\right)$ and carboxylic acid $( COOH )$ group. They are represented by the general formula. where $R =$ alkyl, aryl or any other group.
General Structure of an $\alpha$-amino acid

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Question 34 Marks

What are enzymes?

Answer

Enzymes are biological catalysts. Each biological system requires a different enzyme. So, as compared to conventional catalysts, enzymes are specific and efficient in their action. They are required in only small quantity and work at optimum temperature (310 K) and pH (7.4) under 1 atmospheric pressure. Chemically, they are globular proteins. However, some enzymes are also associated with some non-protein components called the co-factors for their activity. Co-factors are of two types :
(a) Inorganic ions : Such as $Zn ^{2+}, Mg ^{2+}$, $Mn ^{2+}, Fe ^{2+}, Cu ^{2+}, Co ^{2+}$, etc.
(b) Organic molecules : These are of two types :
(i) Co-enzymes : These are usually derived from vitamins such as thymine, riboflavin, niacin, etc. They are loosely held to the protein and can be easily separated by dialysis.
(ii) Prosthetic group : They are also derived from vitamins such as bictin but are tightly held to the protein molecule by covalent bonds. They can be separated only by careful hydrolysis.

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Chemistry 4 Marks Questions

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