Structure and functions of peptides and proteins

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Peptides and Proteins Structure and Functions
R.C. Gupta Professor and Head Dept. of
Biochemistry National Institute of Medical
Sciences Jaipur, India
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Peptides
Peptides are relatively small polymers
Generally, polymers having less than 100 amino
acids are known as peptides those with 100 or
more are known as proteins
E M B - R C G
Many peptides are formed from breakdown of
proteins
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E M B - R C G
EMB-RCG
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Glutathione
Glutathione is a tripeptide
(g-glutamyl-cysteinyl-glycine)
E M B - R C G
EMB-RCG
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E M B - R C G
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E M B - R C G
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Bradykinin
E M B - R C G
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E M B - R C G
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Angiotensin
E M B - R C G
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E M B - R C G
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Oxytocin
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Thyrotropin-releasing hormone (TRH)
PyroglutamateHistidineProline
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Met-enkephalin
Tyr-Gly-Gly-Phe-Met
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Proteins
Large polymers of amino acids
E M B - R C G
Have complex structures
Perform important functions in living organisms
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E M B - R C G
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E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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Structural organization of proteins
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E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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Peptide bonds
E M B - R C G
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EMB-RCG
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Disulphide bonds
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?
Another cysteine residue
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E M B - R C G
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Non-covalent bonds
E M B - R C G
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Hydrogen bonds
E M B - R C G
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Electrostatic bonds
E M B - R C G
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Hydrophobic bonds
E M B - R C G
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E M B - R C G
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E M B - R C G
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Primary structure
E M B - R C G
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Arg-Val-Cys-Ala-Tyr-Lys-Gly-Phe-Ser
Arg-Val-Cys-Ala-Lys-Tyr-Gly-Phe-Ser
Two different primary structures
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E M B - R C G
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E M B - R C G
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E M B - R C G
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Secondary structure
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a-Helix
E M B - R C G
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E M B - R C G
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E M B - R C G
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E M B - R C G
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b-Pleated sheets
Portions of same peptide chain or different
peptide chains running side by side are joined
They are joined by hydrogen bonds formed between
peptide linkages
This produces an extended zigzag structure
resembling a series of pleats
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E M B - R C G
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E M B - R C G
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a-Helix (ribbon)
b-Pleated sheets (arrows)
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Tertiary structure
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E M B - R C G
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E M B - R C G
EMB-RCG
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The spatial arrangement of amino acid residues
forming a specific three-dimensional conformation
constitutes the tertiary structure of the
protein
Tertiary structure
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Quaternary structure
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Sub-unit
Sub-unit
Quaternary structure
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Quaternary structure
Tertiary structure
Secondary structure
Primary structure
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E M B - R C G
EMB-RCG
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Heat
Denatured protein
Native protein
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E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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Addition of urea and mercaptoethanol
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Protein folding
If the primary structure is correct, the
nascent protein will fold spontaneously
E M B - R C G
It will automatically attain higher orders of
structure and the correct conformation
However, spontaneous folding
is a slow process
Rapid and correct folding of the protein is
ensured by some enzymes and proteins
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Proteins involved in folding
E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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Acquired CJD
E M B - R C G
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Human beings who consumed beef from cows having
mad cow disease developed a variant of CJD
E M B - R C G
They had misfolded prion protein in their brains
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Fractionation of proteins
E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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Salt fractionation
E M B - R C G
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E M B - R C G
EMB-RCG
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Alcohol fractionation
Different proteins are precipitated at different
concentrations of alcohol
E M B - R C G
Thus, differential alcohol precipitation can be
used for protein fractionation
Acetone can also be used for this purpose
EMB-RCG
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Centrifugation
E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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Chylomicrons rin
VLDL rin
IDL rin
LDL rin
HDL rin
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Electrophoresis
E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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Bands of serum proteins
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Densitometry of serum proteins
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E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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Chromatography
E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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E M B - R C G
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E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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When the adsorbent is packed into a column, it
is known as column chromatography
E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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Functions of proteins
E M B - R C G
EMB-RCG
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A small change in primary structure can
alter conformation and function of protein
E M B - R C G
EMB-RCG
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E M B - R C G
EMB-RCG
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Structural proteins
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E M B - R C G
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E M B - R C G
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Each polypeptide chain is coiled into a
left-handed helix in which three amino acid
residues are present in each turn
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E M B - R C G
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E M B - R C G
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E M B - R C G
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Two aldehyde groups may undergo aldol
condensation resulting in cross-linking
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Cross-linking may also occur due to formation
of Schiff bases
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E M B - R C G
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E M B - R C G
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E M B - R C G
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E M B - R C G
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E M B - R C G
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E M B - R C G
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E M B - R C G
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E M B - R C G
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E M B - R C G
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Catalytic proteins
E M B - R C G
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E M B - R C G
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Membrane transport proteins
E M B - R C G
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Membrane channels
E M B - R C G
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Contractile proteins
E M B - R C G
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Receptors
E M B - R C G
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Signal transducers
E M B - R C G
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Storage proteins
E M B - R C G
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Carrier proteins
E M B - R C G
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E M B - R C G
EMB-RCG
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Antibodies
E M B - R C G
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E M B - R C G
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Complement proteins
E M B - R C G
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Coagulation factors
E M B - R C G
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Lubricant proteins
E M B - R C G
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Thank you