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1. MSCDFSM BIOCHEMISTRY
LIPIDS AND PROTEIN PART IV

2. PEPTIDES : PEPTIDES are formed by linking aminoacid by peptide bond formation that involves
carboxylic group and an amino group with elimination of water molecule.
.polypeptide and protein are chain of amino acid held together by peptide bond
When two amino acid join they form dipeptide ,when three aa join ,they form tripeptide and
so onwhen more than 10 aa join together they form oligopeptide.each amino acid begin with
amino group and end with carboxylic group .
Physiologically important amino acid :
1. GLUTATHIONE : it is a tripeptidemade up of glutamic acid ,cysteine and glycine .this is
important part of oxidation reduction reaction.
2. Oxytocin and vasopressin: they have 8 amino acids they help in ejection of milk and
reabsorbtion in kidney.
3. Angiotensin : ANGIOTENSIN I and Angiotensin II have 10 and 8 amino acid respectively and
has sight effect on blood parameters.
4. INSULIN : it has 51 amino acid contain 2 polypeptide chain linked together by two s-o-s
bridges.it helps in the utilization of sugar by cells.
PROTEINS :
These are the dehydration products of amino acids with each amino acid residue joined to its
neighbor by specific covalent bond
CLASSIFICATION OF PROTEIN :
1.SIMPLE PROTEIN
2.CONJUGATED PROTEINS
3.DERIVED PROTEIN

3. 1.SIMPLE PROTEIN
Protein that carry only protein and no other compounds are called simple protein eg
.albumin,globulin etc
2.CONJUGATED PROTEINS :
These are the proteins that have non protein part as well with protein part eg .Nucleoprotein
lipoprotein
DERIVED PROTEINS
These proteins are formed from either simple protein or conjugated protein due to unfolding of
tertiary structure or cleavage of peptide bond.eg primary derivatives are proteins and
metaproteins .the secondary proteins are peptones and peptides .
STRUCTURE OF PROTEINS
There are 4 levels of structures :
PRIMARY STRUCTURE
SECONDARY STRUCTURE
TERTIARY STRUCTURE
QUATERNARY STRUCTURE
PRIMARY STRUCTURE : it refers to linear arrangement of amino acid residues in given
polypeptide chain linked through peptide bond.the shortest peptide bond has 20 – 100 amino
acid ,secreating glucagons.

4. Most of protein have 100-150 aa ,rarely they have 1000 aa .the number and sequence of aa
Determine the specificity of protein and slight disturbance can create a new protein .eg.
Haemoglobinwhen glutamic acid is replaced by valine at position no 6 of haemoglobin.it
changes the hb and create the disease of sickle cell anaemia .
Secondary Structure : it refers to 3 dimensional arrangement of various atomof protein
.the polypeptide is folded and secondary confirmation is stabalizeddue to the binding
forces.hydrogen bond,disulphide bond,ionic bondhydrophobic bond are formed
some protein take the shape of coil(α- helix) eg.α –keratin. And some protein posses sheet
(β- pleated sheet )eg. Β –keratin ,collagen .
TERTIARY STRUCTURE :this term refers to tendency of polypeptide chain to undergo
extensive coiling or folding and produce a complex and rigid structure ,stabilized by
intermolecular bonds .like hydrogen ,ionic bond ,hydrophobic bond. And it attains globular
,ellipsoidal conformation.
QUATERNARY STRUCTURE :many protein like enzymes consist of peptide chain linked by
disulphide bond eg. Haemoglobin consist of 4 polypeptide chain,2 α chain and 2β chain
bound together.

5. PHYSIO CHEMICAL PROPERTIES OF PROTEINS
1. Isoelectric PH : many ionisable group are present in protein molecule .depending upon ph
some acts as proton acceptor and some proton donor .thus protein is amphoteric
compounds.at a specific phit act as dipolar ion or also called zwitter ion.this ph is called
isoelectric ph .
2. Soubility : globular protein are generally more solube in aqueous mediumias compare to
kerqtin or fibrous ones .solubility depends on PH ,nature of solvent ,temperature.
3. Precipitation :
isoelectric pH :as they donot have any charge at isoelectric ph ,aa easily become
precipitated.
Salting out : in aqueous medium ,protein can be precipitated by adding TCA (trichloroacetic
acid ) OR PCA (perchloric acid ). Salts of heavy metals ike phosphomolybdic acid or
phosphotungstic acid are used for precipitation.this process is known as salting
out.concentrated solution like MGSO4, NA2SO4 also used for precipitation.
Action of non polar organic solvents : a non polar solvent like chloroform enhances the
electrostatic attraction between ion of proteinand result in precipitation.
Chemical properties of protein are due to side chain.
• Sakaguchi reaction : the arginine side chain each containing a guadinine group react with
α naphthol in presence of sodium hypochlorite to produce red colour.
• Hopkins kole reactions : tryptophane side chainsbeing indolescan react with glyoxylic acid
in presence of concentrated sulphuric acidto form purple colour .

6. • Milion reaction : tyrosine side chains,each possessing a phenolic group undergo variety of
reactionsif it is treated with mercuric sulphate and sodium nitrate red complex is used.
this reaction are used in quantitative analysis.
STRUCTURE AND CLASSIFICATION OF NUCLEIC ACID
1. These arethe polymers of nucleotides .nucleotides are nucleoside phosphate.nucleoside is
composed of nitrogenous base and pentose sugar. nitrogenous base can be purines or
pyrimidines .adenine and guanine comes under purines and cystosine ,uracil,thymine comes
under pyrimidine. Now pentose sugar further of two types ribose sugar or deoxyribose sugar
2. When phosphate group +pentose sugar+ base combine it form nucleoside.
3. When the sugar present is ribose sugar it is calledribonuceotide
4. When the sugar present is deoxyribose ,it is called deoxyribonucleotide.
5. AMP IS most naturally occurring nucleotide.
6. During cellular metabolism,AMP with ADP (adenosine 5 diphosphate ) and adenosine 5
triphosphate (ATP)plays important role in utilization of energy.

7. COMPARISION OF RNA AND DNA
RNA
• Ribonucleic acid
• It has ribose sugar
• It has uracil in place of thymine others are
same
• RNA is single strandedand is made as
complimentary strandof one of the 2 chain of
DNA.
• RNA are small
• There are 3 types of RNA :
• mRNA (MESSENGER RNA ) ; tRNA (transfer
RNA); rRNA (ribosomal RNA).they all have
specific function during protein synthesis.
DNA
• Deoxyribonucleic acid
• It has deoxyribose sugar
• It contains 4 types of nitrogenous base; adenine
,thymine,cytosine,guanine
• It consist of 2 polynucleotide chain coiled around central
helix.the chain is held by hydrogen bond between the
bases of opposite chain . Base pairing relationship is
important to note .adenine always pairs with thymine and
guanine pairs with cytosine .A=T;G=C.