Molecules of The Cell
Short Questions and Answers
One Mark Questions with Answers
1. Energy liberated by catabolic reactions is immediately trapped in
Answer: (c) ATP
2. Basic unit of nucleic acid is
(a) pentose sugar
(b) phosphoric acid
(c) nitrogen base
Answer: (d) nucleotide
3. Purines of DNA are
(a) cytosine and guanine
(b) adenine and guanine
(c) adenine and cytosine
(d) uracil and guanine
Answer: (b) adenine and guanine
4. An enzyme that brings about structural changes of a compound without altering its molecular weight is
Answer: (d) isomerase
5. Specificity of a protein in its enzymatic property depends upon
(a) linear sequence of amino acids
(b) turnover number
(c) active sites
(d) km value
Answer: (a) linear sequence of amino acids
6. Adenine is
Answer: (b) purine
7. Enzymes act by
(a) lowering energy of activation
(b) increasing energy of activation
(c) maintaining energy of activation
(d) without affecting activation energy but increasing reaction time
Answer: (a) lowering energy of activation
8. Coenzyme is
(a) always a protein
(b) often a vitamin
(c) a non protein organic compound
(d) often a metal
Answer: (b) often a vitamin
9. Enzymes required to cut double strand of DNA in genetic engineering is
(b) Reverse transcriptase
(c) Restriction endonuclease
Answer: (c) Restriction endonuclease
10. Enzymes were discovered accidentally in yeast cell extract by
Answer: (c) Buchner
11. Lock and key theory of enzyme action was given by
Answer: (b) Fischer
12. Which are the most diverse molecules of cell?
(d) mineral salts.
Answer: (a) proteins
Two Marks Questions with Answers
1. What are micro and macro molecules?
Answer: Micromolecules are small sized simple chemicals that have low molecular weight, higher solubility and simple conformation. Micromolecules include water, gases, minerals, sugars, amino acids and nucleotides. Macromolecules are large sized complex chemicals that have high molecular weight, low solubility and complex conformation. They usually produce colloidal complex. Macromolecules generally belong to four classes of organic compounds i.e., carbohydrates, lipids, proteins and nucleic acids.
2. What are oligosaccharides?
Answer: Oligosaccharides are small carbohydrates which are formed by condensation of 2-9 monosaccharides. Therefore, oligosaccharides belong to the category of compound carbohydrates (polysaccharides are also compound carbohydrates). Depending upon the number of monosaccharide molecules condense to form oligosaccharides, the latter are known as disaccharides ( for example, sucrose, lactose), trisaccharides (example raffinose), tetrasaccharides (stachyose), pentasaccharide, etc. Large oligosaccharides having branched or unbranched chains occur attached to cell membrane.
3. Differentiate between oligosaccharides and polysaccharides.
Answer: Oligosaccharides contain 2-9 monosaccharide residues while polysaccharides possess a large number of monosaccharide residues. Oligosaccharides are soluble in water while polysaccharides are insoluble. Oligosaccharides are commonly sweet to taste whereas sweetness is absent in case of polysaccharides. The examples of oligosaccharides are sucrose, maltose, raffinose and the examples of polysaccharides are starch, glycogen and cellulose.
4. What are mucopolysaccharides?
Answer: Mucopolysaccharides are slimy substances or mucilages which possess acidic or an animated polysaccharides formed from galactose, mannose, sugar derivatives and uronic acids. Mucopolysaccharides or mucilages are quite common in both plants and animals. They can be observed by cutting the unripe fruits of lady’s finger. The function of mucopolysaccharide is to bind proteins in the cell walls and connective tissue. They provide lubrication in ligaments and tendons.
5. Differentiate between nucleoside and nucleotide.
Answer: Nucleoside is a compound formed by the union of a nitrogen base with a pentose sugar while nucleotide is a compound formed by the union of a nitrogen base, a pentose sugar and phosphate. Nucleoside is a component of nucleotide while nucleotide is formed through phosphorylation of nucleoside. Nucleoside is slightly basic in nature while nucleotide is acidic in nature.
Three Marks Questions with Answers
1. Differentiate between saturated fats and unsaturated fats.
Answer: Saturated fats do not possess any double bonds in their fatty acids while unsaturated fats contain one or more double bonds in their fatty acids. In case of saturated fats all carbon atoms are fully saturated whereas in case of unsaturated fats carbon atoms are unsaturated in the region of double bond. Saturated fats have straight chains while in case of unsaturated fats the chain bends at the double bond. Saturated fats are solid at ordinary temperature while unsaturated fats are liquid at ordinary temperature. Saturated fats have higher melting point while unsaturated fats have lower melting points. Saturated fats increase blood cholesterol and unsaturated fats lower blood cholesterol.
2. Explain the lock and key hypothesis.
Answer: The lock and key hypothesis was put forward by Emil Fischer in 1894. According to this hypothesis both enzyme and substrate molecules have specific geometrical shapes. In the region of active sites the surface configuration of the enzyme is such as to allow the particular substrate molecules to be held over it. The active sites also contain special groups having -NH2, -COOH, -SH for establishing contact with the substrate molecules. The contact is such that the substrate molecules or reactants come together causing the chemical change. It is similar to the system of Lock and key. Just as a lock can be opened by its specific key, a substrate molecule can be acted upon a particular enzyme. This also explains the specificity of enzyme action. After coming in contact with the active site of the enzyme the substrate molecules or reactants form a complex called enzyme-substrate complex. In the complexed state the molecules of the substrate undergo chemical change. The products remain attached to the enzyme for sometime so that an enzyme-product complex is also formed. However, the products of soon released and the freed enzyme is able to bind more substrate molecules.
3. What are allosteric enzymes?
Answer: Allosteric enzymes are enzymes which have separate areas for different types of modulators that alter the conformation of the active site so as to make it effective or ineffective. The areas are called allosteric sites. The substances which cause change in allosteric sites are known as modulators, allosteric substances or effectors. The latter are a two types activators and inhibitors. Allosteric activator binds with an allosteric site in such a way as to make active site operational. Allosteric inhibitior on the other hand, brings about such a change in the active site that it becomes unable to combine with substrate molecules. For example, the enzyme phosphofructokinase is activated by ADP and inhibited by ATP.
4. Differentiate between catalysts and enzymes.
Answer: Catalysts are inorganic in nature while enzymes are proteinaceous in nature. Catalysts are small molecules or simple mineral ions while enzymes are complex macromolecules with three-dimensional structure. Catalysts have comparatively very low molecular weight while enzymes have a high molecular weight. Catalysts operate in the nonliving or physical world while enzymes originate in biological world mediate biochemical reactions. Catalysts are less efficient while enzymes are highly efficient. Catalysts can catalyse diverse reactions while an enzyme catalyses specific reaction of a single or only a few substrates.