Bio Molecules

@ MOLECUTES'

1. Give reason :

(i) The melting points and solubility in water of amino acids are generally higher than that of thecorresponding halo acids.

Ans : Due to the presence of dipolar(Zwitter ion) in Amino acid ,the inter molecular electrostaticforce is strong between them, their melting points and solubility in water is higher .But in halo

acids there is only one hydrogen bonding between their molecules.

(ii) Vitamin B&C can't be stored in our body?

Ans :Vitamin B & C cannot be stored in our body because it is water soluble. As a result, it isreadily excreted in the urine.

(iii) The two strands in DNA are not identical but are complementary.

(iv) sucrose is not a reducing sugar? (2010)

Ans : Because it does not reduce Fehling's solution and Tollen's reagent .

2. List the reactions of glucose which cannot be explained by its open-chain structure.

(2008, Del-2OL2)

Ans : (i) open chain structure of glucose does not give 2,4-DNP test, Schiff's test, and also does

not react with NaHSOg

(ii) The pentaacetate of glucose does not react with hydroxylamine, This indicates that a free

-CHO group is absent from glucose.

(iiiJ The crystallisation of o<-form (m.p. = 419 K) and p-form (m.p = 423k) cannot be explained

by the open chain structure ofglucose.

3. Explain the following terms :

(i) A peptide linkage (2008,2009,2011, Del - zOtZ)

Ans : The amide formed between -C00H group of one molecule of an amino acid and

-NH2 group of another molecule of the amino acid by the elimination of a water molecule is

called a peptide linkage.

HzN -CH -COOH HzN -CH -COOH (_Hzo) HzN -CH -CO -HN -CH -COOH1+1-1LcH(cH3)z cHs cH(crys)z cHs

Valine Alanine Valylalanine I val - ala)

(iiJ A glycosidic linkage (200e)

Ans : A linkage formed between two monosaccharide units through an oxygen atom by the loss

of a water molecule is called glycosidic linkage

!ryry,

GlWn*idieiir*k4ge

* l1 -gluenxt * t}* Sui:tor*

$$w$

(iii) Invert sugar

Ans : The mixture of equimolar solution of of

(ivJ Polypeptides

Ans : The polymer of amino acids which have large number of peptide bonds is called polypeptides.

[v) pyranose structure of glucose

[vi) (a)Denaturation

Ans : A process that changes the physical and biological activity of proteins without changing the

chemical composition of protein is called Denaturation. It is caused by changes in PH,

temperature, presence of salt e't,c'

(b) Effect of denaturation

Effect ofdenaturation on the structure ofproteins:

As a result of denaturation , Secondary and tertiary structures of protein are destroyed, but the

primary structures remain unaltered and so the enzyme loses its activity.

Due to denaturation, the globular proteins(soluble in H2O) get unfolded and helixes get

uncoiled and so changed into fibrous proteins(insoluble in H2O) and their biological activity is

lost. For example,boiled egg which contain coagulated proteins can not be hatched'

(viiJ Enzyme (2ot2)

Ans : Enzymes are proteins that catalyse biological reactions. Globular proteins acts as a

catalyst.

Example: ceH22oy mattase

c6Hpo6

[viii) Biocatalyst (Del - 2012)

Ans : A catalyst which catalyses biological reactions is called Biocatalyst ' Generally enzymes

are considered as biocatalYst.

(ix) Amphoteric behaviour of amino acids?

(?OtO,?OtZ)

glucose and fructose is called invert sugar '

(zoog-F ,zoto,zotz)

(2011)

(2008)

2_

Ans : In aqueous solution, the carboxyl group of an amino acid can lose a proton and the amino

group can accept a proton to give a dipolar ion known as zwitter ion. It is an ion formed by

neutralisation of acidic and basic centres present within the molecule .

llltft" *tn-- t -"-".3 """. 14 @ x *" {:tr - - { *" {t'

'L

:\H- '\ll1

Ir*,itter icm

Therefore, in zwitter ionic form, the amino acid can act both as an acid and as a base.

0rnA[xJ Nucleic acids their two important functions.

A

Nucleic acid is a bio molecule which are found in the nuclei of all living cells in the form of

nucleo proteins or chromosomes.

It is of two rypes.(i) deoxyribonucleic acid [DNA) (ii) ribonucleic acid [RNA)

Two main functions of nucleic acids are:

(D DNA is responsible for the transmission of hereditary effects from one generation to another.

(ii) Nucleic acids (both DNA and RNA) are responsible for synthesis of all proteins essential for

the growth and maintenance of our body.

(xi) Essential amino acids

Ans : That amino acids which cannot be synthesised in our body and must be taken through

food is called essential amino acids. For example: valine and leucine

(xii JNon-essential amino acids (2010)

Ans : That amino acids which can be synthesised in our body are called Non-essential amino

acids , For example: glycine, and alanine

4. How are vitamins classified? Name the type of vitamin, their chemical name, deficiency

disease and source.

On the basis of their solubility in water or fat, vitamins are classified into two groups.

(i) Fat-soluble vitamins: Vitamins that are soluble in fat and oils, but not in water, Example:

Vitamins A, D, E, and K

(iiJ Water-soluble vitamins: Vitamins that are soluble in water. B group vitamins (81,82,86'

812, etc,) and vitamin C. Vitamin 812 is insoluble in water and store in liver. (2009)

However, biotin or vitamin H is neither soluble in water nor in fat.

Vitamin Chemical name Deficiencv disease Source of vitaminA Retinol(bright

eye vitamin)Xerophthalmia i.e.hardening ofcornea or night blindness

Cod liver oil, shark liveroil,carrot, rice polishing,liver,kidnev

'I

B1 Thiamine Beri-Beri: disease of nervoussvstem.

Milk, rice,yeast,nuts,eggs,sreen vesetables,

B2 Riboflavin Glossitis[dark redtongue),dermatitis andcheilosis[fissuring at cornersof mouth and lipsl

Turnip, milk, eggs,yeast,vegetables,liver,kidney

B5 Pyridoxine Dermatitis and convulsions Meat, fish,egg yolk,wholecereal.srams

Bo Cyanocobalamine Pernicious anaemia(RBCdeficient in haemo-slobin')

Mea! eggs, Iiver of ox,fish,sheep

C Ascorbic acid Scurvy(bleeding of gum),Pyorrhea

Citrous fruits like orange,lemon,tomato,greenveeetable

D Ergocalciferol Rickets[bone deformities inchildren) & Osteomalacia [softbones and joint pains inadults)

Exposure to sun light,fish,egg yolk,cod liver oil

E Tocopherols Sterility,increase fragility ofRBCs and muscular weaken-ss

Oils like cotton seed oil,sovabean oil, sun flower oil

K Phvlloouinone Increased blood clottins time Cereals,leafv veeetables

H Biotin Dermatitis, Ioss of hair andparalvsis.

Yeast, liver,kidney and milk.

5. [a) Name the products of hydrolysis of :

(iJ sucrose. (2010)

Ans : Sucrose on hydrolysis gives equal amount of Glucose & Fructose:

cpH22oy+ H2o Inlrertase>

c6Hpo6 + CoHnoo

This reaction is also called enzyme catalysed reaction'

(ii) Maltose

Ans : Maltose on hydrolysis gives two molecules of glucose :

[iii) Lactose

Ans : Lactose on hydrolysis yields equal amounts of D(+)glucose and D(+) galactose,

(b) What are reducing sugars and non-reducing sugars ?

Ans : Those carbohydrates which reduces Fehling's solution and Tollen's reagent are called

reducing sugars. AII monosaccharides and disaccharides, excluding sucrose, are reducing

sugars.

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Those carbohydrates which do not reduce Fehling's solution and Tollen's reagent are called

non-reducing sugar.

(c) State clearly what are known as nucleosides and nucleotides' (2010)

Ans : Nucleotide : - The repeating units of nucleic acid is called nucleotide. It consists of Nitrogen

containing base, 4 carbon sugar and a phosphate group'

Complete hydrolysis of a nucleotide from DNA containing thymine will yield;

(i) phosphoric acid (ii) p - D - 2 - Deoxy ribose sugar [iii) Thymine,cystosine (pyrimidine)

(iv) adenine and guanine.

Nucleoside ;- It is a nitrogen containing base like purines and pyrimidines and has 4 carbon

sugar. Nucleoside on hydrolysis gives a sugar,two purines and two pyrimidines'

(dJ Name the four bases present in DNA . Which one of these is not present in RNA . (2009)

Ans : DNA contains, Adenine, Thymine, Guanine and Cytosine ' Thymine is not present in RNA

(e) Name the bases present in RNA. Which one of these is not present in DNA ' (20tL)

Ans : Uracil , Cytocine, Guanine, Adenine are present in RNA. Uracil is not present in DNA'

(f) Mention the names of the bases produced on hydrolysis of DNA . (2010)

Ans: Thymine, Guanine and CYtosine

(g)Write two main functions of carbohydrates in plants' (2008- F)

Ans : Two main functions of carbohydrates in plants are:

(i) In making cell wall of bacteria and plants

(ii) It acts as a biofuel and provide energy for the functioning of living system'

(h) Write the reaction of D-glucose with the following reagents? (2008 - F)

ti) HI (iil Bromine water [iii) HN03

When D-glucose is heated with HI for a long time, n-hexane is formed.

rifi)IIilt

tt rI0,th -t--} CbE-z * t3\* Ct{2-*ffH; *(}t1* fftlI

Cffg{}tt n - bex*ne

t)* gilaar*e

(ii) When D-glucose is treated with Br2 water, D- gluconic acid is produced'

I

{1{{}

I((rlt)Hu

I

Br: wfil*r

(sfit{

I(?H*lLl,,

CH2CIH

I}-.g{Leirx

fll{*flfl{

1) - glur:rse

c14,a$ra

D * gtam*it **irX

{o{}Hli*cd**xe a*iri

(iii) On being treated with HNO3, D-glucose get oxidised to give saccharic acid.

CIfi} CSCII{

| ffr$*1 tt+t$lq{ -*-*-*--}, ((}li$t}4ll

(i) What are the different types of RNA found in the cell?

Ans: (i) Messenger RNA [m-RNA) (ii) Ribosomal RNA (r-RNA) (iii) Transfer RNA [t-RNA)

[) When RNA is hydrolysed , there is no relationship among the quantities of different bases

formed . What does this fact suggest about the structure of RNA ? (2008 O.D. Comp)

Ans : It suggest that A pairs with U and C pairs with G is not followed . Thus unlike RNA has

single brand .

6. Distinguish between the following :

[i) Globular and Fibrous proteins.

S.N. Fibrous proteins Globular proteins

ti) It has thread like structure. It has soherical shape.

riil It is usually insoluble in water. It is usuallv soluble in water.

riiil It forms B - pleated structure' It formsa - helix.(iv) It has H-bonds in some cases

between polypeptide chains.It has intramolecular H-bonds, disulphidelinkages,ionic or salt bridges and hydrophobicinteraction.

(ii) Amylase and AmYIoPectin

S.N. amylase amvlopectin

I It is soluble in water It is insoluble in water

2 It is a Ions straight chain It is lons branched chain

3 It sives blue colour with iodine It does not give blue colour with iodine

(iii) a- helix and p - pleated sheet structure.

S.N. a- helix B - oleated sheet structure

ti) The peptide chain coils and acquire a

coil shape

The peptide chain coils and acquire a

B - nleated sheet structure

tiD Intra molecular H-bonding takesplace.

lntermolecular H-bonding takes place.

S.N. a- slucose B -slucoseril Its specific rotation is +1110 Its specific rotation is +19.20

riil Its polvmer is readily disested. Its polvmer is not digested.

[ivJ a- glucose and P -glucose

[v] Glycogen and Starch.

(viiJ Elastomers and Fibres (2008 -o.D.)

(vii) Structural and Functional differences between DNA

The structural differences between DNA and RNA are as follows:

The functional differences between DNA and RNA are as follows:

S.N, DNA RNA

DNA undereoes replication . RNA does not undergo replication .

riil It is responsible for hereditary effects. It controls the synthesis of proteins.

7. [aJ Write the main structural difference between DNA and RNA.0f the four bases, name those which

are common to both DNA and RNA. (?OL].,Del - ZOLZ)

(b) Of the two bases named below, which one is present in RNA and which one is present in DNA

[i) Thymin (ii) Uracil (20l2,Del-2OLZ)

Ans : (i) Thymine is present in DNA (ii) Uracil is present in RNA

[c) Mention the type of Iinkages responsible for the formation of the following : (2008 O.D')

1

Clvcosen Starch

Glycogen is a branched chain polymer of a

- glucose similar to amylopectinStarch is a mixture of amylopec-tin(branched chain polymer of amylaseand linear polymer of a-glucose).

Elastomers Fibres

1. They are rubber like solid with elastic properties They are thread like solid with high tensilestrenqth.

2. They are held together by weakestintermolecular forces .

They are held together by strong intermolecularforces like H - bondine..

3.Example : Buna-S &Buna- N. Nvlon 6.6 and polvesters .

S.N, DNA RNA

(i) Its molecular mass varies from six tosixteen million.

Its molecular mass varies from twentyto forw thousands.

II DNA contains thvmine [T) . RNA contains uracil [u).riiil DNA contains double helix structure RNA contains sinsle helix structure.

[i) Primary structure of proteins

(iii) a - helix formation

Ans: [i) peptide linkage

(iiiJ H - bond

(ii) Cross - linking of polypeptide chains

(ivl f-sheetstructure

(ii) polypeptide linkage

[iv) IntermolecularH - bond

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