ashok protein chemistry
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Contents
IntroductionProtein and peptidePeptide bond and its MachanismCharacteristics of peptideMethods of peptide synthesisProtein structure(Linus pauling structure)
INTRODUCTION
• As muscles and tendons they provide the body with the means for movement; as skin and hair they give it an outer covering.
• Proteins are polyamides, and their monomeric units are composed of about 20 different a-amino acids.
• Proteins occur in every living organism, are of many different types, and have many different biological functions.
• The three groups of biological polymers are polysaccharides, proteins, and nucleic acids.
• As enzymes and hormones, proteins catalyze and regulate the reactions that occur in the body.
PROTEIN
AND
PEPTIDE
• Oligopeptide is formed of (2 – 10 ) amino acids: 2 amino acids dipeptide, 3 amino acids tripeptide, 4 amino acids tetrapeptide ….etc.• Polypeptide is formed of more than 10 amino
acids
• All proteins are polymers of amino acids.
• Each protein polymer (polypeptide chain) consists of a sequence of 20 different amino acids connected together by peptide bonds.
• For chains under 40 amino acid residues, the term peptide is frequently used instead of protein.
Peptide
bond
• This is a dehydration synthesis reaction (also known as a condensation reaction).
• The four-atom functional group -C(=O)NH- is called an amide group or (in the context of proteins) a peptide group.
• Peptide bond is an amide linkage between the carboxyl group of one amino acid and the amino group of another amino acid formed by condensation reaction with removal of one molecule of water.
Mechanism
of
peptide bond
N
H
H CH
COO
R
AMINO ACID
H2O H2O
N
H
H CH
H
C
R
O
N
CH
H
COO
R
PEPTIDE GROUP
Charac
teris
tic
s
of p
eptid
e
• Cis and Trans Peptide Bonds
• Resonance
C
O
N C
O
N
C
O
C
N
C
H
alfa c atom
alfa c atom
C N
O
C
H
Calfa C atom
alfa C atom
CH
O
CH2
N
H2C
H
cis trans
Methods of
peptide
Synthesis
[coupling method]
CouplingDeprotection
Formation of peptide bond it is necessary that the OH Group present in the carboxylic acid function is convert into a good leaving.
COOH group is to convert in to acyle group.In this method ,the protected amino acid is converted to the corresponding acyl chloride followed by reaction with amino acid or ester under Schotten - -Baumann condition or treatment with amino ester in organic solvents to give the N- protected peptide.Deportection under hydrolytic condition give the free peptide.
2HNHC
R
COOHSOCl2
NHC
R1
COCl
H
H
2HNHC
R2
C
O
OCH3
2HNHC
R1
C
O
N
H
HC
R2
COCH3HC C
O
N
H
HC
R2
COOH
R1
N
H
H
Protein
structure
• Structure of protein divided into 4 levels.• Primary structure• Secondary structure• Tertiary structure• Quaternary structure
• Protein molecule can be formed of one or more polypeptide chains which may vary in the number and sequence of amino acid residues.
primary
structue
N CH C
R
N
O
*
H H
HC C N
O
R
H
HC
R
C
O
n
Primary structure of protein refers to linearSecquence of amino acid in its polypeptide chain . It represent the number,nature and Sequence of amino acid molecule in the poly--peptide chain. Example:- simple polypeptide chain.
Secondary
structure
and
Linus
pauling
It results by hydrogen bonding between carboxylic oxygen and amide hydrogen atom of the component amino acid of the peptide chain. These hydrogen bonded arrangement ,if present ,are called secondary structure of protein.
• These bond can occure either with in the molecule of one polypeptide chain forming alpha-helix plated sheet.
• The alpha-helix structure of protein was first proposed by Linius pauling and Robert corey using X ray analysis of protein.
• In the alpha-helix (look like the right hand screw) conformation,the polypeptide chain form of spiral staircase.
• The coil of helix are held together by hydrogen bond laying parallel to the main axis and all side chain extend outward form the axis of the spiral.
• Such a structure is flexible and elastic but it gives stability of the peptide chain.
The folding of linear polypeptide chain in to a specific arrangement, represents the secondary structure of a protein molecule.
Linus Carl
Pauling
• "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances"
Example : - hairs protein ,nails protein etc.
Tertiary and
Quaternary
structure
The quaternary structure involves the non covalent association of two or more peptide chain in protein molecule.
Having more than peptide chain so called oligomers. In this structure same kind of interaction that hold the individual
protein chain in a particular three dimensional conformation. They are hydrophobic interactions, hydrogen bond and electro- -
static interaction. It decribe the way of subunits are arrange in space.
Example: hemoglobin form a globular protein.
Tertiary structure of a protein is the final three dimensional shape due to folding its poly- peptide chain.
Protein folds in solution have maximum stability due to that occur in folding are covalent –bond ,hydrogen bond and vanderwaals or hydrophobic interaction.
Example –alpha Keratin,fibrous- protein
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