UNIT-14
Biomolecules
Biomolecules-These are those organic compounds which build up living organisms and
are required for their growth and maintenance are called biomolecules,for example,
carbohydrates,,proteins,vitamins,hormones etc
Carbohydrates- These are the poly hydroxy aldehydes or ketones or those compounds
which produce these on hydrolysis
Glyceraldehyde
Classification of Carbohydrates-
* Monosaccharides-These are those carbohydrates which cannot be hydrolysed
further to give simpler carbohydrates.The general formula is (CH2O)n Wheren=3 to 7
Oligosaccharides-These are those carbohydrates which give two to ten
monosaccharide molecules on hydrolysis.They include
Disaccharides- Which produce two monosaccharide molecules on hydrolysis.e.g
sucrose and maltose and lactose etc.Their general formula is C12H22O11 .
Remainder (i) Hydrolysis product of maltose is two molecules of glucose
(ii) Hydrolysis product of Sucrose is glucose and fructose
(iii) Hydrolysis product of lactose is glucose and glactose
Trisaccharides-Which produce three monosaccharide molecules on hydrolysis. e.g
Raffinose, which on hydrolysis gives one molecule of each glucose,fructose and
galactose. Their general formula is C18H32O16
Polysaccharides- These are those carbohydrateswhich on hydrolysis produce a large
number of monosaccharide molecules. e.g Cellulose,Starch,glycogen etc. Their general
formula is (C6H10O5)n
.where n= 100 to 3000. (Imp) (2018)
Q-Which polysaccharide component of carbohydrates is commonly present in bread ? (2017)
Ans- Starch
Sugars – All the monosaccharides and oligosaccharides are crystalline solids,soluble
in water and sweet in taste are called sugars.
Non-Sugars- All the polysaccharides are amorphous solids, insoluble in water and tasteless are called
Non-sugars.
* Classify the followings into monosaccharides and disaccharides:
Ribose, 2-deoxyribose,maltose,glactose,fructose and lactose
Ans- Monosaccharides- Ribose, 2- deoxyribose,galactose and fructose.
Disaccharides- Maltose and lactose
Anomers: Such pairs of optical isomers which differ in configuration only around C1
atom are called anomers. E.g. α-D-glucopyranose and β-D- glucopyranose
(2014)
Epimers: Such pairs of optical isomers which differ in
configuration around any other C atom other than C1 atom are called epimers. E.g. D-glucose
and D-mannose are C2 epimers
Epimers: Such pairs of optical isomers which differ in
configuration around any other C atom other than C1 atom are called epimers. E.g. D-glucose
and D-mannose are C2 epimers.
Q- What are the products of hydrolysis of sucrose ?(2014)
Ans- Giucose and Fructose
Reactions of glucose- Acylation
Q- Glucose on reaction with acetic acid gives glucose pentaacetate .What it
suggest about the structure of glucose ?
Ans- It confirms the presence of five –OH groups in glucose. As glucose exist as a
stable compound, five –OH groups should be attached to different carbon
atoms.(2018)
* Glycosidic Linkage- The two monosaccharide units are joined together by an
oxide linkage formed by the loss of a water molecule is called glycosidic
linkage.
Difference b/w glycogen and starch- Both starch and glycogen are homopolysaccharides
because they consists of only one kind of monomer(𝛼 − 𝐷 𝑔𝑙𝑢𝑐𝑜𝑠𝑒 )
Starch- It is made up of two components Amylose(unbranched structure having 1 -4
glycosidic linkage) and amylopectins(branched structure having both 1 -4 and 1-6 glycosidic
linkage)
2. Starch is produced in plants and stored form of plants.3 It has both branched and
unbranched components.4.It has branching after 24-30 alpha glucose residue.5 It is less
branched
Glycogen- It is made up of one component-Amylopectins 2.Glycogen is produced in animals
and stored form of animals.3 It has branched components. It has branching after 8-12 alpha
glucose residue.5. It is highly branched
* Basic structural difference b/w starch and cellulose
- Starch consists of amylose and amylopectin.Amylose is a linear polymer of
alpha-D-glucose while cellulose is a linear polymer of beta-D-glucose. In
amylose, C-1 of one glucose unit is connected to C-4 of the other through
alpha- glycosidic linkage.However, in cellulose,C-1 of one glucose unit is
connected to C-4 0f the other through beta-glycosidic linkage. (2016)
Q-Which of the two components of starch is water soluble ? (2014)
Ans-Amylose
* Reducing carbohydrates or reducing sugars -These are those which reduces
Fehling’s reagent or Tollen’s reagent. e.g monosaccharides and disaccharides
Non-reducing carbohydrates - These are those carbohydrates which do not
reduce Fehling’s reagent
or Tollen’s reagent. e.g All the polysaccharides(starch,cellulose etc)
Importance of carbohydrates-1. It act as structural components of cells. 2. It act
as biofuels and provide energy for the functioning of the living system. 3.They
provide raw materials for many industries like textiles,paper etc. 4. It is found in
biosystem in combination with many proteins and lipids.
*Two main functions of carbohydrates in plants- 1) Cellulose acts as the
structural material for plant cellwalls. 2) Starch is the major reserve food
material in the plants. It is stored in seeds and acts as the reserve food
materials for the tiny plant till it is capable of making its own food by
photosynthesis.
Amino Acids- These are those organic acids havingan amino group attached
to a chain containing an -COOH group.
Neutral amino acids contain one amino group and one carboxyl group.Acidic
amino acids contain one aminogroup and two carboxyl groups.Basic amino groups
contain two amino groups and one carboxyl group.
*Essential Amino acids-These are those amino acidsthat cannot be synthesized
by the body and supplied in diet e.g valine, lysine (2018)
*Non-essential Amino acids-These are those aminoacids that can be synthesized
in our body. e.g glycine,alanine,praline etc.
Zwitter ion-The carboxyl group can lose a proton and the amino group can
accept a proton in their aqueous solution.
*Amphoteric behavior of amphoteric acids-It is due to dipolar structure, amino
acids are amphoteric in nature.The acidic nature of amino acids is due to the
NH3+ group and basic nature is due to COO ̶ group (2015,2018)
Iso-electric point- At certain pH the dipolar ion exists as a neutral ion and does not
migrate to either electrode is known as iso-electric point of the amino acid.
* Peptide linkage- The bond formed between amino group of one α –amino
acid and carboxyl group of other α –amino acid is called peptide linkage.
Proteins- They are polyamides, and derived from the α-amino carboxylic acids.A
single protein molecule contains thousands of amino acid units.
Classification based on Composition
Fibrous Protein-In this type, the proteins consist of linear molecules which are
placed side by side to form fibres. The different polypeptide chains are held by
intermolecular hydrogen bonding. These are usually insoluble in
water.Examples Keratin, myosin.
Globular protein- In this type,the proteins has spheroidal shapes.The different
polypeptide chains are held by intramolecular hydrogen bonding.These are
usually soluble in aqueous solutions.Examples enzymes, hormones,
haemoglobins.
Q-Give one example of globular and fibrousprotein.(2016)
*Effect of denaturation on the structure of proteins. Denaturation of proteins-
When proteins are heated or acted upon by reagents like alcohols,heavy metal
salts, picric acid etc,proteins are coagulated and lose their structure and
biological activities. This phenomenon is called denaturation of proteins (2018)
Classification according to hydrolysis products
1. Simple proteins-These are the proteins which when hydrolysed, form
only α-amino acids. e.galbumins, globulins etc.
2. Conjugated proteins- In this case, a protein partis linked to non-protein
part called prosthetic group.e.g nuclein, mycin
3. Derived proteins-These are the proteins formed by the partial hydrolysis of
simple conjugated proteins such as proteoses, peptones, peptides.
* Primary Structure of proteins- It refers to the covalently bonded structure of
an amino acid and the order in which the amino acids are joined along the
chain. Any change in the primary structure, thesequence of amino acids
creates a different proteins
*Secondary Structure of proteins-It arises due to the regular folding of the backbone
of the polypeptide chain due to intramolecular hydrogenbonding between carboxyl and
amino groups
It can be classified into two types
α –Helix-The α –Helix structure is found in many proteins such as keratin
(found in hair) and myosin (found in muscles).These proteins are elastic.On
stretching, the weak intramolecular hydrogen bondsare broken and on
releasing the tension, the hydrogen bonds are reformed,restoring the original
shape
β –pleated sheet structure-This structure is obtained, when intermolecular
hydrogen bonds areformed b/w amide groups of two different protein chains. In
this conformation all peptide chains are stretched out laid side by side to form a flat
sheet
*Bonding stabilizes the alpha-helix structure of proteins-Intermolecular
hydrogen bonding b/w C=Oof one amino acid residue and the N‒H of the
fourth amino acid residue in the chain.
Q Write two types of secondary structure ofproteins (2017)
Q- Give one difference between α –Helix and β
–pleated sheet structures of
proteins.(2018)
Tertiary structure of protein- The tertiary structurearises due to folding, coiling
and bending of polypeptide chains producing three-dimensional structures.The
two molecular shapes found are fibrous such as silk collagen and keratin have
rod-like rigid shape and are insoluble in water.On the other hand other is
globular such as hemoglobin have spherical shape.
Quaternary structure of protein- The quaternary structure refers to the
determination of number of sub-units which may be identical or different
held together by non covelent forces such as hydrogen bonds,electrostatic
interactions and vander waal's interactions and their arrangement in an
aggregateprotein molecule.
*Enzymes-These are naturally occurring , simple orconjugated proteins acting
as catalysts in the biochemical reactions in the living systems
Prosthetic group-A number of enzymes possess anon -protein part is called
prosthetic group.
Coenzymes-Those prosthetic groups which get attached to the enzyme at the
time of reaction arecalled coenzymes. Examples riboflavin
Modes of enzyme action- An enzyme combine witha reactant to form
intermediate compound which affords a lower energy reaction pathway and is
more reactive than initial uncombined species
E + S → E–S → P + E
Enzyme Substrate Product
Nucleic acid- These are polynucleotides which are formed by combining a large
number of nucleotidemolecules with the simultaneous elimination of water
molecules.
Q What type of linkage is present in nucleic acids ?(2016)
Ans- Nucleic acids shows phosphodiester linkage.Nucleotide-
Eeterification of one of the hydroxyl groups of the sugar part of the
nucleoside with phosphoric acid converts a nucleoside into nucleotide
Nucleotide = Base + sugar + Phosphate Nucleoside- A base sugar
unit formed by the combination of sugar and nitrogeneous base is
called Nucleoside.
Nucleoside = Base + Sugar
Mutarotation- The process of change in specific rotation of an optically active
compound in solutionis called mutarotation.
Mutation-The chemical change in the basesequence in the DNA
strand.
Gene-The DNA base sequence which acts as the code for a specific protein
synthesis is known as agene.
Genetic code-The relationship b/w the nucleotidetriplets and the amino
acids used in protein synthesis is called genetic code.
Replication- The property of DNA to build exact copies of its own molecules
is known as replication.Translation- It involves the synthesis of protein under
instruction from m-RNA.
Transcription-It involves the formation of RNA froma DNA template.
RNA- Nucleic acids which contains sugar D-riboseare called ribonucleic acids
or RNA.
DNA-Nucleic acids which contains sugar D-2- deoxyribose are called deoxy-
ribonucleic acids orDNA
Functions of nucleic acids:- They are of two types(1)DNA (2).Their functions
are-
Functions of RNA – 1. Messenger RNA(m-RNA) – Itcarries the message of
DNA
for specific protein synthesis.
2. Ribosomal(r-RNA)- It provides the site where the protein synthesis takes
place but carries no message.
3. Transfer RNA(t-RNA)- It transfers amino acids to the site of protein synthesis.
Functions of DNA- 1. It controls the synthesis of proteins in the living cells.
2. It has the property of building up exact copies ofI its own molecule,This
property is called replication.
3. It causes mutation and which is responsible for structural and
functional changes in subsequent generations.
Difference B/w DNA and RNA (V Imp)
Structural differences
RNA 1. It contains the sugar ribose in its nucleotides. 2. It contains
cytosine and uracil as pyrimidine bases in it. 3. It is mainly formed in the
cytoplasm in the cell. 4. It is a single stranded molecule.
.DNA- 1. It contains the sugar 2-deoxyribose in its nucleotides. 2. It contains
cytosine and thymine aspyrimidine bases in it.3.It is mainly found in the
nucleus of the cell.4. It is a double stranded
Q- Name the base that is found in nucleotide ofRNA only.(2018)
Functional differences
DNA-(1) DNA has unique property of replication (2) DNA controls the
transmission of hereditary effects.RNA-(1) RNA usually does not replicate (2)
RNA controls the synthesis of proteins.
*The two strands in DNA are not identical but arecomplimentary-The two
strands in DNA molecule are held together by hydrogen bonds b/w purine
base of one strand and pyrimidine base of other
and vice-versa. Because of the different sizes and geometries of the
bases,the only possible pairing in DNA are G(guanine) and C(cytosine)
through three hydrogen bonds and between A(adenine) and T(thiamine)
through two hydrogen bonds.Due to this base pairing principle,the sequence
of bases in one strand automatically fixes the sequence of bases in the other
strand. Thus,the two strands are complimentary and not identical.
Vitamins-These are biomolecules which are required in small amounts for the
growth and health of human beings and animals.
Types of Vitamins
Water insoluble vitamins-These includes VitaminsA, D , E , and k. These are
fat soluble.
Water soluble vitamins- These includes vitamins B,H and C. These are soluble
in water.
Give two examples of water soluble vitamins(2017)
Some important vitamins and their deficiencydiseases (VImp)
*VitaminA- Night blindness, xerosis(drying of
skin),xerophthalmia(cornea becomes opaque)
Source-milk,butter,egg,fish etc.
Vitamin B - B1(Thiamine) Beriberi( paralysis of legs),B2(R(iboflavin)
Cheilosis(fissuring of cornersof mouth and lips),digestive disorders and
burningsensation of skin. B6(Pyridoxine) Convulsions B12
anaemia(bloodlessness)
Source- egg, milk,rice,wheat,meat etc.
*VitaminC- Scurvy(bleeding of gums), pyorrhea(loosening of teeth and
bleeding of gums)Source- oranges, lemon,grape,cabbage etc
Vitamin D- Rickets(bending of bones) ( Imp) (2018)Source-
eggs,fish,butter,meat etc
*Vitamin K- haemorrhage(blood clotting)Source- green leafy
Structure of amylose
Structure of Amylopectin
Structure of Cellulose
Important questions
28. Glucose on reaction with acetic acid gives glucose penta acetate
.What does it suggestsabout the structure of glucose ?
Ans- It conferms the presence of five –OH groupsin glucose.As glucose exist as a
stable compound,five –OH groups should be attached to different carbon atoms.
29. Write one difference between α-helix and -pleated structures of
proteins.
Ans - α-helix structure of proteins hasintramolecular hydrogen bonding while
-pleated structure of proteins has intermolecularhydrogen bonding
30. Glucose on reaction with acetic acid gives glucose penta acetate
.What does it suggestsabout the structure of glucose ?
Ans- It conferms the presence of five –OH groupsin glucose.As glucose exist as a
stable compound,five –OH groups should be attached to different carbon atoms.
31. Write one difference between α-helix and -pleated structures of
proteins.
Ans - α-helix structure of proteins has intramolecular hydrogen bonding while
-pleated structure of proteins has intermolecularhydrogen bonding.
32. What is invert sugar ?
Ans- It is an edible mixture of two simple sugarsglucose and fructose that is made
by heating
