NCERT Exemplar Class 11 Biology Solutions Biomolecules

NCERT Exemplar Class 11 Biology Solutions Biomolecules

Multiple Choke Questions
1.It is said that elemental composition of living organisms and that of inanimate objects (like earth’s crust) are similar in the sense that all the major elements are present in both. Then what would be the difference between these two groups?
Choose a correct answer from the following.
(a) Living organisms have more gold in them than inanimate objects.
(b) Living organisms have more water in their body than inanimate objects.
(c) Living organisms have more carbon, oxygen and hydrogen per unit mass than inanimate objects.
(d) Living organisms have more calcium in them than inanimate objects.
Soln.(c): A comparison of elements present in non-living and living matter is given in the table below:

2.Many elements are found in living organisms
either free or in the form of compounds. One of the following is not found in living organisms,
(a) Silicon (b) Magnesium
(c) Iron (d) Sodium
Soln.(a): Various mineral elements present in living organisms include (i) major elements carbon (C), nitrogen (N), oxygen (O), hydrogen (H), phosphorus (P), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K) and chlorine (Cl) and (ii) trace elements, iodine (I), iron (Fe), manganase (Mn), cobalt (Co), copper (Cu), zinc (Zn), molybdenum (Mo), boron etc.

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3.Amino acids have both an amino group and a carboxylic acid group in their structure. Which amongst the following is an amino acid?
(a) Formic acid (b) Glycerol
(c) Glycolic acid (d) Glycine
Soln.(d): Glycine is the simplest amino acid with hydrogen as R group. Formic acid is simplest carboxylic acid molecule. It is chemically HCOOH. Glycerol is a polyol compound, which is chemically propane-1, 2, 3-triol and glycolic acid is chemically, 2-hydroxyethanoic acid.

4.An amino acid under certain conditions have both positive and negative charges simultaneously in the same molecule. Such a form of amino acid is called
(a) acidic form
(b) ba’sicform
(c) aromatic form
(d) zwitterionicform.
Soln.(d) :

In neutral solution, an amino acid molecule exists as a dipolar ion (zwitter ion) i.e., molecule containing positive and negative ionic groups. The charge on the ion changes with pH. In an acidic solution (low pH) the amino acid picks upH⁺ ions and becomes positively charged. In alkaline solution (high pH) the amino acid donates H+ ions to the medium and becomes negatively charged. The pH at which the amino acid is electrically neutral or the molecule exists as a zwitterion is called the isoelectric pH.

5.Which of the following sugars have the same number of carbon as present in glucose?
(a) Fructose (b) Erythrose
(c) Ribulose (d) Ribose
Soln. (a): Fructose and glucose, both are
six carbon sugars having formula C₆ H₁₂ O₆ Erythrose is a four carbon sugar. Ribulose and ribose are both five carbon sugars.

6.An acid soluble compound formed by
phosphorylation of nucleoside is called
(a) nitrogen base
(b) adenine
(c) sugar phosphate
(d) nucleotide.
Soln.(d) : Nucleoside is basically pentose sugar + nitrogenous base. Nucleotide is pentose sugar + nitrogenous base + phosphate group. DNA and RNA are composed of nucleotides.

7.When we homogenise any tissue in an acid the acid soluble pool represents
(a) cytoplasm (b) cell membrane
(c) nucleus (d) mitochondria.
Soln.(a): The acid soluble pool has roughly similar composition as that of cytoplasm. Biomolecules with molecular weights in the range of 18 – 800 Daltons come in acid- soluble fraction (with the exception of lipids). Though, the macromolecules from cytoplasm and organelles represent the acid-insoluble fraction.

8.The most abundant chemical in living organ-isms could be
(a) protein (b) water
(c) sugar (d) nucleic acid.
Soln.(b)

9.A homopolymer has only one type of building block called monomer repeated ‘n’ number of times. A heteropolymer has more than one type of monomer. Proteins are heteropolymers usually made of
(a) 20 types of monomers
(b) 40 types of monomers
(c) 30 types of monomers
(d) only one type of monomer.
Soln.(a): The function and shape of a protein is affected by sequence of 20 types of amino acids, each having an amino group -NH₂, a carboxylic acid group -COOH, a hydrogen atom each attached to carbon located next to -COOH group and a side chain R which varies from one amino acid to other. (It can be hydrogen or an aliphatic group, an aromatic or heterocyclic group).

10.Proteins perform many physiological functions. For example, some proteins function as enzymes. One of the following represents an additional function that some proteins performs.
(a) Antibiotics
(b) Pigment conferring colour to skin
(c) Pigment making colours of flowers
(d) Hormones.
Soln.(d) :Most of the body functions are regulated by hormones like growth, vegetative and sexual development, thermal regulation, cellular oxidation, metabolism of carbohydrates, proteins, fats etc. Hormones are needed in very small quantity to carry out these functions. Some hormones are proteinaceous, e.g., insulin (regulates sugar metabolism), growth hormone of pituitary, parathyroid hormone i.e., parathormone (regulates Ca and phosphate transport).

11.Glycogen is a homopolymer made up of (a) glucose units (b) galactose units (c) ribose units (d) amino acids.
Soln.(a): Glycogen is a branched polymer of glucose. It is readily soluble in water. It consists of a-D glucose units, mostly linked by 1-4, a glycosidic linkage, and is highly branched via frequent 1-6 linkages. Glycogen is found mostly in muscles and liver of animals and is also called animal starch. It gives red colour with iodine solution. It has about 30,000 glucose residues and a molecular weight of about 4.8 million. The straight part is helically twisted with each turn having six glucose units. The distance between two branching points is 10-14 glucose residues. In a polysaccharide chain of glycogen, the right end is called reducing end and the left end is called non-reducing end.

12. The number of ends’ in a glycogen molecule would be
(a) equal to the number of branches plus one
(b) equal to the number of branch points
(c) one
(d) two, one on the left side and another on the right side.
Soln.(a)

13. The primary structure of a protein molecule has
(a) two ends   (b) one end
(c) three ends (d) no ends.
Soln.(a): Primary structure of a protein is simply the amino acid sequence of it which has two ends the carboxyl and amino terminals.

14. Which of the following reactions is not enzyme- mediated in biological system?
(a) Dissolving C02 in water
(b) Unwinding the two strands of DNA
(c) Hydrolysis of sucrose
(d) Formation of peptide bond
Soln.(a) : DissolvingC0₂ in water does not require any enzyme. C0₂ has higher solubility in water than 02. Solubility of C0₂ in water can be increased with decrease in temperature, a principle used in carbonated drinks.

Very Short Answer Type Questions
1.Medicines are either man made (i.e., synthetic) or obtained from living organisms like plants, bacteria, animals etc. and hence the latter are called natural products. Sometimes natural products are chemically altered by man to reduce toxicity or side effects. Write against each of the following whether they were initially obtained as a natural product or as a synthetic chemical.
(a) Penicillin________
(b) Sulfonamide________
(c) Vitamin C________
(d) Growth hormone_______
Soln.
(a) Natural
(b) Synthetic
(c) Natural
(d) Natural

2.Select an appropriate chemical bond among ester bond, glycosidic bond, peptide bond and hydrogen bond and write against each of the following.
(a) Polysaccharide
(b) Protein
(c) Fat
(d) Water
Soln. (a) Glycosidic bond
(b) Peptide bond
(c) Ester bond
(d) Hydrogen bond

3.Write the name of any one aminoacid, sugar, nucleotide and fatty acid.
Soln. Amino acid – Lysine Sugar – Fructose
Nucleotide – Adenosine monophosphate Fatty acid – Palmitic acid

4.Reaction given below is catalysed by
Soln.oxidoreductase between two substrates A and A’, complete the reaction. A reduced + A’ oxidised >
HDOxidoreductase is an enzyme that takes part in oxidation and reduction reactions. This enzyjne is involved in transfer of electrons from one molecule called as electron donor to another molecule called electron acceptor. The complete reaction is :

5.How are prosthetic groups different from co-factors?
Soln. Co-factors are the non-protein constituents of conjugated or compound enzymes, associated with the apoenzyme of the enzyme (protein portion). Co-factor is small, heat-stable and dialysable part of conjugate enzyme. It may be inorganic, e.g., Ca, Fe, Cu, Zn etc. or organic (e.g. prosthetic group and coenzyme). Prosthetic groups are non-protein organic cofactors firmly attached to the apoenzymes, e.g., haem, biotin, etc.

6.Glycine and alanine are different with respect to one substituent on the a-carbon. What are the other common substituent groups?
Soln. General formula of amino acid is —

In Glycine, R is represented by hydrogen (H) and in alanine, by methyl group(CH₃).  COOH,H₂N and H are common substituent groups in both glycine and alanine.

7.Starch, cellulose, glycogen, chitin are polysac-charides found among the following. Choose the one appropriate and write against each.
Cotton fibre________
Exoskeleton of cockroach_________
Liver________
Peeled potato________
Soln.
Cotton fibre – cellulose
Exoskeleton of cockroach – chitin
Liver – glycogen
Peeled potato – starch

Short Answer Type Questions
1.Enzymes are proteins. Proteins are long chains of aminoacids linked to each other by peptide bonds. Aminoacids have many functional groups*in their structure. These functional groups are, many of them at least, ionisable. As they are weak acids and bases in chemical nature, this ionization is influenced by pH of the solution. For many enzymes, activity is influenced by surrounding pH. This is depicted in the curve below, explain briefly.

Soln. Everv enzyme has an optimum pH when it is most effective. A rise or fall in pH reduces enzyme activity by changing the degree of ionisation of its side chains. A change in pH may also start reverse reaction. Fumarase catalyses  fumarate -> malate at 6.2 pH and reverse at 7.5 pH. Most of the intracellular enzymes function near neutral pH with the exception of several digestive enzymes which work either in acidic range of pH or alkaline, e.g., 2 pH for pepsin and 8.5 pH for trypsin.

2.Is rubber a primary metabolite or a secondary . metabolite? Write four sentences about rubber.
Soln. Rubber is a secondary metabolite. Natural rubber is a polymer of 2 methyl-1, 3-butadiene which is more commonly known as isoprene. Its molecular weight is typically between 100,000 and a million which is equivalent to between 1500 and 15000 monomer units. Rubber is extracted from latex which is a milky suspension produced by plants to heal wounds. Latex has rubber, water, resins, terpenes, proteins and sugars. Latex is collected from rubber trees using a process called tapping. In natural state rubber deforms easily but is not very elastic because the long, unbranched polymer can easily slide past each other. It is also very tacky, which makes it useful for application such as adhesives. However, for a majority of its uses rubber is crosslinked using sulphur in a process called vulcanisation.

3.Schematically represent primary, secondary and tertiary structures of a hypothetical polymer say for example a protein.
Soln.Primary structure of a protein includes number of polypeptides, number and sequence of amino acids in each polypeptide.

The development of new stearic relationships of amino acids present in linear sequence inside the polypeptides leads to the formation of secondary structure of proteins.

Tertiary structure involves interactions that are caused by binding and folding of a-helix or P sheets leading to the formation of rods, spheres or fibres. Tertiary structure is stabilised by several types of bonds such as, H-bonds, ionic bonds, covalent bonds, van der Waal’s interactions hydrophobic bonds, etc.

4.Nucleic acids exhibit secondary structure, justify with example.
Soln. Nucleic acids show a wide variety of secondary structures. DNA or deoxyribose
nucleic acid is a helically twisted double chain polydeoxyribonucleotide macromolecule. A DNA molecule has two unbranched comple¬mentary strands. They are spirally coiled. The two spiral strands of DNA are collectively called DNA duplex. The two strands are not coiled upon each other but double strand is coiled upon itself around common axis. The double helical structure of DNA is stabilised by phosphodiester bond, hydrogen bond and ionic interactions.
5. Comment on the statement “living state is a non-equilibrium steady state to be able to perform work”.
Soln.Metabolites or biomolecules occur in organisms in concentrations characteristic of each of them. The living systems maintain this concentration of biomolecules because they are in metabolic flux, always remaining in nonequilibrium steady state where equilibrium is seldom achieved. No work can be carried out in equilibrium state. Therefore, living systems are regularly receiving an input of energy to prevent reaching an equilibrium and remain always in nonequilibrium steady state. Energy is obtained from metabolism. Metabolism and living state are, therefore, complementary. There cannot be a living state without metabolism.

Long Answer Type Questions
1.Formation of enzyme-substrate complex (ES) is the first step in catalysed reactions. Describe the other steps till the formation of product.
Soln.Each enzyme has an active site. The active sites of enzymes have a specific conformation for attracting and holding substrate. 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 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 by a particular enzyme. After coming in contact with the active site of the enzyme, the substrate molecules or reactants form a complex called enzyme-substrate complex. The active site of enzyme is now in close proximity with the substrate and break its chemical bonds and a new enzyme product complex is formed. The products are soon time so that an enzyme-product complex is also formed. However, the products are soon released and the freed enzyme is able to bind more substrate molecules.

Thus we see that the chemical reactants do not cause any alteration in the composition or physiology of the enzyme. The same enzyme molecule can be used again and again. Hence, enzymes are required in very small concentrations.

Upper series – Breakdown reaction Lower series – Biosynthetic reaction

2.What are different classes of enzymes? Explain any two with the type of reaction they catalyse.
Soln. According to International Union of Biochemistry (IUB) enzymes are grouped into the following six categories.
(i) ’Oxidoreductases : They take part in oxidation and reduction reactions or transfer of electrons.

Oxidoreductases are of three types- oxidases, dehydrogenases and reductases, c.g., cyto-chrome oxidase, succinate dehydrogenase, nitrate reductase.
(ii) Transferases : They transfer a group from one molecule to another c.g., glutamate pyruvate transaminase (transfers amino group from glutamate to pyruvate during synthesis of alanine). The chemical group transfer does not occur in the free state.

(iii) Hydrolases : They catalyse hydrolysis of bonds like ester, ether, peptide, glycosidic, C—C, C—halide, P—N, etc. which are formed by dehydration condensation. Hydrolases break up large molecules into smaller ones with the help of hydrogen and hydroxyl groups of water molecules. The phenomenon is called hydrolysis. Digestive enzymes belong to this group, e.g., amylase (hydrolysis of starch) sucrase, lactase.

(iv)Lyases : These enzymes cause cleavage, removal of groups without hydrolysis, addition of groups to double bonds or removal of a group producing double bond, e.g., histidine decarboxylase (breaks histidine to histamine and COz), aldolase (fructose-1, 6-diphosphate to dihydroxy acetone phosphate and glyceraldehyde phosphate).

(v)Isomerases : These enzymes cause rearrangement of molecular structure to effect isomeric changes. They are of three types, isomerases (aldose to ketose group or vice-versa like glucose 6-phosphate to fructose 6-phosphate), epimerases (change in position of ope constituent or carbon group like xylulose phosphate to ribulose phosphate) and mutases (shifting the position of side group like glucose-6-phosphate to glucose-1- phosphate).

(vi)Ligases (Synthetases) : These enzymes catalyse bonding of two chemicals with the help of energy obtained from ATP resulting in formation of such bonds as C—O, C—S, C—N and P—O, e.g., pyruvate carboxylase. It combines pyruvic acid with C02 to produce oxaloacetic acid.
Pyruvic acid + C0₂ + ATP + H_zO

3.Nucleic acids exhibit secondary structure. Describe through Watson-Crick Model.
Soln.Nucleic acids are long chain
macromolecules which are formed by end to end polymerisation of large number of repeated units called nucleotides. Nucleic acids show a variety of secondary structures. There are two types of nucleic acids – deoxyribonucleic acid or DNA and ribonucleic acid or RNA. Deoxyribonucleic acid (DNA) is genetic material found in the nucleus of all living cells with the exception of some viruses. The structure of DNA was elucidated by Watson and Crick based on X-ray diffraction studies. They proposed a double helix model of DNA. According to this model, DNA exists as a double helix and consists of two strands of polynucleotides that are antiparallel to each other, i.e., both run in opposite directions, one in 5′ -> 3′ direction and other in 3′ -> 5′ direction.
The backbone of DNA strand is formed by alternate sugar and phosphoric acid group. The phosphate group is connected to carbon 5’of the sugar residues of its own nucleotide and 3′ of the sugar residue of the next nucleotide by phosphodiester bonds.The nitrogen bases are projected more or less perpendicular to the backbone of DNA and face inside. A and G of one strand base pair with T and C respectively on the other strand. Between A and T (A=T), there are two hydrogen bonds while, there are three hydrogen bonds between G and

4.What is the difference between a nucleotide and nucleoside? Give two examples of each with their structure.
Soln. Differences between nucleoside and nucleotide are as follows :

5.Describe various forms of lipid with a few examples.
Soln. Lipids are fatty acids esters of alcohols and related substances which are insoluble in water but get dissolved in a number of non-polar organic solvents like ether, benzene, chloroform, acetone, etc.
Depending upon their composition and characteristics lipids are often classified into . simple lipids, compound lipids and derived lipids.
(i) Simple lipids – These are formed from fatty acids and alcohol. They do not have any additional group, e.g., fats, suberin, cutin, wax.
(a) Neutral or true fats – They are triglycerides which are formed by esterification of three molecules of fatty acids with one molecule of trihydric alcohol, glycerol (glycerine or trihydroxy propane). Three molecules of water are eliminated.
In fats the three fatty acids are only rarely similar (e.g., tripalmitin, tristearin, triolein). They are called pure fats. Usually they are dissimilar or two of the three fatty acids are similar. They are known as mixed fats, e.g., Butter. Fats are named after the names of fatty acids, e.g., dipalmito-stearin, palmito-oleio-stearin, steario-oleio-palmitin.
(b) Waxes – They are fatty acid esters of long chain monohydric alcohols like cytyl, ceryl or mericyl.
(c) Cutin – It is a complex lipid produced by cross-esterification and polymerisation of hydroxy fatty acids, as well as other fatty acids with or without esterification by alcohols other than glycerol.
(d) Suberin – It is a mixture of fatty material having condensation products of glycerol and phellonic acid or its derivatives.
(ii)Compound or conjugated lipids: These are the esters of fatty acids and alcohol but contain other substances also, e.g., phospholipid, glycol’ipids, sphingolipids etc.
(a) Phospholipids- They are triglyceride
lipids where one fatty acid is replaced
by phosphoric acid which is often linked to ‘additional nitrogenous groups like choline (in lecithin), ethanolamine (in cephalin), serine or inositol. ”
(b) Sphingolipids – They are lipids
having amino alcohol sphirigosine.
Sphingomyelins contain an additional
phosphate attached to choline like
phospholipids.
(c) Glycolipids – These are sugar containing
lipids, in which the lipids portion of the
molecule is usually based on glycerol or sphingosine and the sugar is typically
galactose, glucose or inositol.
(iii)Derived lipids: These are lipid-like substance such as sterol or derivatives of lipids, e.g., steroids, prostaglandins and teapenes.
(a) Steroids – They are a group of complex
lipids that possess a hydrogenated
cyclopentano-perhydrophenanthrene
ring system.
(b) Prostaglandins – They are derivatives
of arachidonic acid and other 20 carbon
fatty acids.
(c) Terpenes – They are lipid like hydrocarbons
formed of isoprene (C5H8) units. Steroids like cholesterol are also derived from terpenes having 6 isoprene units. .
Fats are also differentiated into two main
types, on the basis of their melting points at room temperature as follows.
(a) Hard Fats are solids at room temperature and contains long chains of fatty acids, e.g., Animals fat.
(b) Oils are usually liquid at room temperature
because they have low melting point, e.g.,
groundnut (peanut) oil, cotton seed oil, mustard oil, etc.

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