Understanding Biochemistry: The Essential Study of Biological Molecules and Life Structures

of science that deals with the study of the chemical composition and the structure of living organisms

and also various chemical changes taking place within them is called biochemistry

the complex organic molecules which form the basis of life which build up living organisms and are

also required for their growth and maintenance are called biomolecules biomolecules are related to the living

organisms in the sequence living organism organs

tissues cells organelles

and biomolecules the cell the cell is the fundamental unit of life

it is too small to be seen with naked eyes it can be seen with the help of a microscope

cells are packets of chemicals essential for life the cell has the ability to grow and

divide to produce cells these daughter cells can further divide to produce new progeny of cells

cells may be combined to form tissues tissues may be grouped into organs and organs may be combined into organisms

a living cell contains about 50 elements the most abundant substance in a living cell is water which amounts to about 70

percent of the weight in addition to water the cell contains a large number of

carbon compounds carbohydrates carbohydrates constitute an important

class of compounds like glucose fructose

sucrose starch cellulose etc which play a vital role in

our everyday life are defined as polyhydroxy aldehydes or polyhydroxy ketones or the compounds

which can be hydrolyzed to them they are also known as saccharides these are the ultimate source of most of

our food they are derived mainly from plants the name carbohydrate was given to the

compounds pertaining to general formula cxh2oy classification of carbohydrates

carbohydrates are classified into three major categories depending upon their behavior towards

hydrolysis monosaccharides oligosaccharides

and polysaccharides monosaccharides these are simple carbohydrates which

cannot be hydrolyzed to still simpler carbohydrates for example

glucose and fructose oligosaccharides these are the carbohydrates which on

hydrolysis give two to nine units of monosaccharides they have subcategories depending upon

the actual number of monosaccharide units formed by the hydrolysis of a particular oligosaccharide

disaccharides give two units of monosaccharides on hydrolysis for example maltose and sucrose

trisaccharides give three units of monosaccharides on hydrolysis for example raffinose

tetrasaccharides give four units of monosaccharides on hydrolysis for example

stacchios polysaccharides these are the carbohydrates which are

polymeric molecules and can be hydrolyzed to give large number of monosaccharide units

for example starch glycogen and cellulose

monosaccharides monosaccharides containing aldehyde group are called aldosis

while those containing ketonic group are called ketosis

they can be further classified into different categories depending upon the number of carbon

atoms monosaccharides with 3 4 5 6 and 7 carbon atoms are called trioses

tetrosis pentoses hexoses

and heptosis respectively three main aldo hexoses which occur widely in nature are

d-glucose d-galactose and d-mannose

the letter d before the name of monosaccharides represents the configuration as derived

from glyceraldehyde glyceraldehyde is represented by two enantiomeric configurations

glucose c6h12o6 glucose occurs in nature in free state

as well as in combined state in free state it occurs in sweet fruits and honey

ripe grapes contain up to 20 glucose in combined state glucose is present in disaccharides and

polysaccharides maltose and starch on hydrolysis yield only

glucose the methods of preparation of glucose are following

by hydrolysis of cane sugar it can be prepared by hydrolysis of cane sugar in the presence of alcohol

using dilute hydrochloric acid glucose and fructose are formed in equal amounts

glucose is less soluble in ethyl alcohol than fructose so it crystallizes out

by hydrolysis of starch on commercial scale it is prepared by hydrolysis of starch by boiling it with

dilute sulfuric acid at 393 kelvin under a pressure of 2 to 3

bar chemical reactions of glucose the open chain structure of glucose

contains one aldehydic one primary alcoholic group

and four secondary alcoholic groups in fischer projection carbon atoms which are at the

intersection of the lines are not shown with hydrogen cyanide glucose forms an addition product called

glucose cyanohydrin glucose reacts with hydroxylamine to form corresponding oxime like

aldehydes glucose reacts with phenyl hydrazine to form phenyl hydrozone

it reacts with acetic anhydride to form penta acetate which confirms that glucose molecule

contains five hydroxy groups with mild oxidizing agent glucose is oxidized to gluconic acid

with strong oxidizing agent glucose is oxidized to glucaric acid on reduction with sodium amalgam glucose

is reduced to sorbitol a hexahydric alcohol when glucose treated with a dilute

solution of an alkali it undergoes reversible isomerization to form an equilibrium mixture of

d-glucose d-mannose and d-fructose it reduces tolerance reagent failing solution and benedict solution

cyclic structure of glucose some evidence suggests that the open chain structure of d-glucose exists

primarily in equilibrium with two cyclic forms many reactions indicate the absence of

cho group it is found to exist in two different crystalline forms which are named as

alpha and beta the alpha form of glucose is obtained by crystallization from a concentrated

solution of glucose at 303 kelvin while the beta form is obtained by crystallization from hot and saturated

aqueous solution at 373 kelvin it exhibits muta rotation

the change in specific rotation of an optically active compound to an equilibrium value is known as muta

rotation these observations are attributed to the fact

that sugars generally exist in the form of cyclic hemiacetal or hemiketal structures

and only a very small number of molecules exist in open chain structure hoeworth

structures as a result of cyclization the enumeric carbon becomes asymmetric and the newly formed o h group may be

either on the left or on the right in fissure projection this results in the formation of two

isomers the isomers having the hydroxyl group to the right of c1 is designated as alpha

d-glucose the isomers having the hydroxyl group to the left of c1 is designated as beta

d-glucose the lower thickened edge of the ring in howard's structure is nearest to the

observer the groups to the right in fischer projection are written below the plane

of the ring in the hogwarts structure the groups to the left in fissure projection

are written above the plane of the ring in the horwood structure fructose

fructose is a simple monosaccharide found in many plants it is one of the three dietary monosaccharides along with

glucose and galactose that are absorbed directly into the bloodstream during digestion

it is found along with glucose in the juices of ripe fruits and in honey it is also called

levulose because naturally occurring fructose is levorotatory

in combined state it occurs in sucrose and polysaccharide called inulin

on commercial scale it is prepared by hydrolysis of inulin with dilute h2so4

properties of fructose the important properties of fructose are following

it also exists in two cyclic forms which are formed by reaction of o h and c5 to ketonic group at c2

the ring thus formed is a five-membered ring and it has furanos structure

it also shows muta rotation it is colorless crystalline solid and having a sweet taste

it is more soluble in water and alcohol than glucose it also reduces failing solution

benedict's solution and tolerance reagent disaccharides

those carbohydrates which yield two units of monosaccharide on hydrolysis are called disaccharides

for example sucrose yields alpha d-glucose and beta-defructose on hydrolysis

this means the disaccharides are formed by condensation reaction between two

monosaccharide units hemiacetals of monosaccharides undergo condensation between their oh

groups with the elimination of water molecule the bond which holds the monosaccharide

units together is called glycoside linkage all disaccharides are crystalline solid

soluble in water and fall into two classes reducing sugars

if the reducing center of any monosaccharide unit is free the disaccharide is reducing

non-reducing sugars if the two monosaccharide units are linked through their respective carbonyl

groups the disaccharide would be non-reducing sucrose

sucrose is the most widely occurring disaccharide and is found in all photosynthetic plants

it is white crystalline solid and soluble in water when heated above its melting point

it forms a brown substance called caramel it is commercially obtained from

sugarcane and sugar beets when sucrose is hydrolyzed by dilute acids or enzyme inverters

it gives an equimolar mixture of d-glucose and d-fructose sucrose is dextro rotatory with specific

rotation of plus 66.5 degrees on hydrolysis

sucrose gives an equimolar mixture of dextro rotatory glucose and levo rotatory for maltose

starch is hydrolyzed by the enzyme diastase maltose is formed as one of the products

on hydrolysis with dilute acids one mole of maltose yields 2 moles of d-glucose

maltose is a reducing sugar in maltose the two d-glucose units are linked

through alpha-glycosidic linkage between c1 or one glucose unit and c4 of the other

it tastes sweet and it is not found freely in nature it has the ability to reduce the felling

solution due to its free aldehyde the aldehyde group is oxidized giving a

positive result which means that the maltose is soluble in water

in aqueous solution it exhibits muta rotation lactose

lactose is a disaccharide sugar derived from galactose and glucose lactose crystals have a characteristics tomahawk

shape that can be observed with a light microscope it is found mostly notably in cow milk

it makes up around two to eight percent of milk it is used in the pharmaceutical

industry it is added to pills as a filler because of its physical properties and low price

polysaccharides polysaccharides are polymers of monosaccharides joined together by

glycosidic linkage these are known as glycons polysaccharides that are polymers of a

single monosaccharide are called homo polysaccharides a homo polysaccharide

consisting of glucose monomeric units is called a glucan three important polysaccharides in which

all are glucans starch glycogen

and cellulose they are polymers of glucose and differ from each other in molecular weight

the nature of linkage between glucose molecules and degree of polymer chain branching

glycogen glycogen is a multi-branched polysaccharide that serves as a form of

energy storage in animals and fungi in humans it is made and stored primarily in the cells of the liver and

the muscles and functions as the secondary long-term energy storage it is a polymer of glucose with 1 4

alpha glucosidic linkage and having considerable chain branching it is white powder soluble in water it

gives purple color with iodine molecular weight of glycogen is very high

and ranges from 2 into 10 raised to the power 5 to 10 raised to the power 8.

it is found in nearly all animal tissues liver is the principal site in which it is stored

when body needs glucose for energy enzymes break glycogen down to glucose in proteins

proteins are the most abundant biomolecules of the living system chief sources of proteins are milk

cheese pulses peanuts fish meat etc

they occur in every part of the body and form the fundamental basis of structure and functions of life

they're also required for growth and maintenance of body proteins perform a vast array of

functions within living organisms including catalyzing metabolic reactions replicating dna

responding to stimuli and transporting molecules from one location to another amino acids

these are amino substituted carboxylic acids the alpha amino acids are the building blocks of peptides and proteins

in alpha amino acids the amino group is present on the alpha carbon atom

amino acids are classified as neutral acidic or basic depending upon the relative number of

amino and carboxyl groups in the molecule neutral amino acid

if the number of amino groups and carboxyl groups is equal in the molecule the amino acid is neutral

for example glycine basic amino acid

if the number of amino groups is more than carboxyl groups then the amino acid is basic

for example lysine acidic amino acid

if the number of amino groups is less than carboxyl groups then the amino acid is acidic for

example aspartate essential and non-essential amino acid

amino acids can be synthesized by all living organisms plants and animals the amino acids which can be synthesized

in the body are known as non-essential amino acids many animals are not able to synthesize

all the amino acids they need for their proteins those amino acids which cannot be

synthesized in the body and must be obtained through diet are called essential amino acids

for an adult human there are 10 essential amino acids deficiency of essential amino acids in

the diet may cause diseases such as quashoca peptide polypeptide and proteins

enzymes can cause alpha amino acids to polymerize to give peptides through elimination of water molecule

the conh linkage that forms between the amino acids is known as a peptide bond or peptide linkage amino acids when

joined in this manner are called amino acid residues the polymers that contain many amino

acid residues are called polypeptides polypeptides are linear polymers one end of a polypeptide chain

terminates in an amino acid residue that has an nh2 group is known as n-terminal the other terminates in an amino acid

residue with cooh group is known as c-terminal proteins are molecules that contain one

or more polypeptide chains and have molecular mass higher than ten thousand

the precise order of bonding in a peptide is called its amino acid sequence

the amino acid sequence is specified by using three letter amino acid abbreviations for the respective amino

acids and connected by hyphens classification of proteins proteins can be classified into two

broad classes on the basis of their structure fibrous proteins

and globular proteins fibrous proteins when polypeptide chains run parallel

and are held together side by side at many points by hydrogen and disulfide bonds a thread-like structure is formed

such proteins are called fibrous proteins they are insoluble in water

they serve as the chief structural material of animal tissues

for example keratin in skin hair

nails horn and wool globular proteins the polypeptide chain in these proteins

is folded around in such a manner so as to give the protein molecule almost spheroidal shape

they have weak intermolecular forces they are soluble in water they catalyze biological reactions

for example insulin and thyroglobin they act as regulators of metabolic

processes for example maintains blood sugar level they act as antibodies and protect the

body from diseases structures of proteins the structures of proteins are quite

complex there are four levels at which the structure of proteins can be described

primary secondary tertiary

and quaternary structures primary structure the sequence in which various amino

acids are arranged in a protein is called its primary structure any change in the sequence of amino

acids creates different protein which alters biological functions secondary structure

it refers to shape in which a long polypeptide chain exists they have two types of structures

alpha helix structure and beta pleated structure the alpha helix structure results due to

regular coiling of polypeptide chain which is stabilized by intramolecular hydrogen bonding

for example keratin in beta pleated sheet structure all

peptide chains are stretched to nearly maximum extension and then arranged side by side and held

together by intramolecular hydrogen bonding for example silk

tertiary structure it represents further folding of the secondary structure

quaternary structure some of the proteins are composed of two or more polypeptide chains referred to

as subunits the spatial arrangement of these subunits with respect to each other is

known as quaternary structure enzymes are biological catalysts they are generally globular proteins which

act as biological catalysts in living systems they have the remarkable ability to

cause reactions to take place faster for example if enzymes were not present in our

digestive tract it would take about 50 years to digest a single meal some common and important

characteristics of enzymes are their action is highly specific each enzyme catalyzes only a specific

reaction enzyme speed up uncatalyzed reaction to a very large extent

their efficiency is maximum at about 310k temperature at a moderate ph even very small amounts of an enzyme are

sufficient to speed up a reaction mechanism of enzyme action the substrate molecule binds itself to

the active sites on the surface of the enzyme the active site in a given enzyme is so

shaped that only a specific substrate can fit in it just like a lock and key the specific

binding results in the formation of enzyme substrate complex enzymes lower down the activation energy

of the reaction for example activation energy of acid hydrolysis of

sucrose is 6.22 kilo joule per mole but activation energy is only 2.15 kilojoule per mole

when hydrolysis takes place in presence of sucrase enzyme humans their sources and deficiency

diseases vitamin a is soluble in oils and fats but insoluble in water

it is essential for growth and vision vitamin b1 is soluble in water and destroyed by heat

vitamin b2 is soluble in water it is stable to heat and destroyed by light deficiency of vitamin b6 causes nervous

disturbances and convulsions vitamin b12 is soluble in water and also contains cobalt

it is red crystalline in nature vitamin c is soluble in water it is destroyed by cooking and exposure to air

it maintains healthy skin and helps in development of body resistance against diseases

vitamin d is soluble in fats and oils but insoluble in water it is stable towards heat and oxidation

vitamin e is soluble in fats and oils but insoluble in water it is stable to heat and oxidation

vitamin h is neither soluble in fat nor in water vitamin k is soluble in fats but

insoluble in water it is stable to heat and oxidation nucleic acid

nucleic acids are long chain polymers of nucleotides they play an important role in transmission of hereditary

characteristics and biosynthesis of proteins proteins combined with nucleic acids are

called nuclear proteins the nucleic acids are of two types deoxyribonucleic acid

and ribonucleic acid nucleic acids contain two types of n-containing heterocyclic bases purine

and pyrimidine purine bases adenine and guanine belong to purine

bases because they contain heterocyclic compound as present in purine

pyrimidine it is the parent substance of a group of compounds which include cytosine

thiamine and uracil which are constituents of nucleic acids dna and rna

deoxyribonucleic acid it contains a pentose sugar deoxyribose and adenine guanine

thiamine and cytosine bases a phosphate group is present at c5 of the sugar unit

the repeating units of deoxyribonucleotides are linked by phosphate group

thus they are the biopolymers of deoxyribonucleotides and have double helix structure of

polynucleotides the two strands of dna are said to be complementary to each other

they are the carrier of genetic characteristics and send information and instruction to the cell for the

synthesis of specific protein ribonucleic acid it contains ribose sugar

bases from pyrimidine bases and two bases from purine base a phosphate group is present at c5 of

the sugar unit the repeating units ribonucleotides are linked by phosphate

group they are the polymers of ribonucleotide and have a single helix structure

rna is associated with the process of learning and memory storage and helps in biosynthesis of protein

biological functions of nucleic acid heritage transfer the double helix of dna is the

storehouse of the genetic information of the organism the process by which a dna molecule

produces two identical molecules of itself in the nucleus of the cell is called replication

protein synthesis it plays a major role in the synthesis of protein

this is brought about in two steps transcription which is copying of sequence of bases from the dna strand on

the rna molecule is called transcription translation in this process mrna directs protein synthesis in the

cytoplasm of cell with involvement of transfer rna and ribosomal particles

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