1. Protein is made up of amino acids that are linked together through peptide bonds to form polypeptide chains. The sequence and structure of these chains determines the protein's function. 2. There are four levels of protein structure: primary, secondary, tertiary, and quaternary. The primary structure is the sequence of amino acids. Secondary structures include alpha helices and beta sheets. Tertiary structure involves folding into a 3D shape. Quaternary involves multiple protein subunits. 3. Examples of important proteins and their structures include hemoglobin, which has a quaternary structure to transport oxygen in red blood cells, and collagen which has a triple helix structure that provides structure and connective

1. PROTEIN
Presented by INSHA UR RAHMAN
Presented to MISS ASIA FAZAL
Sub: Biochemistry
DPT BATCH-I (SEM-III)
KIHST
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2. Introduction
• Protein derived from the Greek word “proteios” meaning “of the first rank”.
• Protein is a polymer consist of repeating units of Amino acid (monomers).
• Amino acids act as a building block of proteins.
• Every protein synthesised in accordance with instructions contained in DNA.
• They act as biological catalyst (enzyme).
• Participate cell signal and recognition factor.
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3. Basic Structure of Protein
• Amino acid is building block of protein.
• More than 20 amino acids combine thru peptide bond form a polypeptide chain
(protein).
• Carboxyl group of one amino acid and amino group of other amino acid combine
thru peptide bond by releasing water molecule.. This process is called as
“Condensation”.
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6. Structure of Protein
The structure of protein depends upon the special arrangement of
polypeptide present in a molecule.
I. Primary structure
II. Secondary structure
III. Tertiary structure
IV. Quaternary structure.
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7. Primary structure
• The sequence of amino acids in a protein is called primary structure of protein.
• Amino acids combine thru peptide bond.
• Each component Amino acid in a polypeptide chain is called a “residue” or
“moiety”
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8. Diagrammatic representation of primary
structure
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• The end of the peptide with a free carboxyl group is called the carboxy-
terminus or C-terminus.
• The terms amino-terminus or N-terminus describe the end of the sequence with a
free α-amino group
• Chain always start with N-terminus
• A specific sequence of nucleotides in DNA is transcribed into mRNA
(Transcription) which is read by the ribosome in a process called translation
• proteins have unique amino acid sequences, which defines the structure and
function of that protein
• The sequence of a protein can be determined by methods called Edman
degradation
• For example, insulin is composed of 51 amino acids in 2 chains. One chain has 31
amino acids, and the other has 20 amino acids.

10. Characteristics of Peptide bond.
• Peptide bond has partial double bond feature that is shorter than single bond.
• Bond is rigid and planar & prevent free rotation around bond b/w carbonyl
carbon and nitrogen of peptide bond.
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11. Secondary structure
• Peptide chains may acquire spiral shape or may be present in a zig zag manner.
This zig-zagging of chain is called secondary structure.
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It consists of
α-helix
β-sheet (composed of β-
strands)
β-bends ( reverse, β-turns)
Nonrepetitive secondary
structure
Supersecondary structures
(motifs)

12. Contd…….
α-Helix
• It is rigid & right handed spiral structure.
• A very diverse & most common group.
• spiral structure, consisting of a tightly packed, coiled polypeptide
backbone core, with the side chains of the component amino acids
extending outward from the central axis.
• stabilized by extensive hydrogen bonding.
• Amino acids 3 or 4 residues apart in primary sequence.
• The H-bond form b/w the O of C=O and Of each peptide bond in
the strand and the H of the N-H group of the peptide bond four
amino acid below it in the helix.
• Each turn of helix contains 3.6 amino acids.
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13. Contd…
• Some amino acids disrupts an α-helix like:
1. Proline
• its secondary amino group is not geometrically compatible with the
α-helix
• inserts a kink in the chain
2. charged amino acids (glu, arg, asp, his, lys)
• disrupt the helix by forming ionic bonds, or by electrostatically
repelling each other. 13

14. Contd…..
β-Sheet
• Form of secondary structure in which all peptide bond components are involved in
hydrogen.
• Because beta-sheet appears “pleated” they are often called β-pleated sheet.
• Sheet is formed by two or more peptide chains (β-strands) aligned laterally &
stabilised by H-bonds b/w carboxyl & amino groups of amino acid.
• the H-bonds are perpendicular to the polypeptide back bone.
• H-bond found between the two strands, the O of C=O in one strand with the H of
the Amino group of the adjacent strand (Interchain bond)
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16. Parallel and antiparallel sheets:
• polypeptide chains of β-sheets are arranged either
Parallel
• Adjacent polypeptide chains running in the same direction.
• formed by a single polypeptide chain
folding back on itself.
Antiparallel
• when the adjacent polypeptide chains
run in opposite direction
• More stable due to well-aligned H-bond
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18. Contd…..
β-bends (reserve turn,β-turn)
• composed of four amino acids, one of which may be proline—the amino acid that
causes a “kink” in the polypeptide chain. Glycine (simplest amino acid).
• Reverse the direction of a polypeptide chain to get folded structure, helping it form a
compact, globular shape
• often include charged amino acids
• usually found on the surface of protein molecules
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19.  Nonrepetitive secondary structure
• Approximately one half of an average globular protein is
organized into repetitive structures, such as the α-helix and/or β-
sheet
• the remainder of the polypeptide chain is described as having a
loop or coil conformation
• They may be irregular or unique.
• 50% of globular proteins are nonrepetitive
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20.  Supersecondary structures (motifs)
• Globular proteins are constructed by combining secondary structural elements (α-
helices, β-sheets, nonrepetitive sequences).
• These form primarily the core region—that is, the interior of the molecule.
• They are connected by loop regions (for example, β-bends) at the surface of the protein.
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22. Tertiary Structure
• Twisting or folding polypeptide chains, three dimensional structure represents
tertiary structure of protein.
• Tertiary refers to both folding of domain & to final arrangement of domains in
polypetide.
• Bondings that stabilize the structure are disulphide bonds (-s-s-) covalent
linkage, hydrophobic interaction, hydrogen bonds & ionic interaction.
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23. Contd…
The three-dimensional & stabilized structure of globular protein is due to
the:
• Hydrophobic interactions (Interior of the chain b/w uncharged Amino acids)
• Hydrophilic Interaction (at the surface of chain b/w Charged Amino acids)
• Hydrogen bonds (b/w polar groups of amino acids on the surface of proteins)
• Ionic interactions (b/w charged amino acid)
• Disulfide bonds (formed from the sulfhydryl group (–SH) of each of two cysteine
residues (separated from each other by many amino acids) to produce a cystine
residue.
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25. Contd…
• fundamental functional and three-dimensional structural units of
polypeptides
• Form by Folding of the peptide chain
• Polypeptide chain have >200 amino acids in length generally consist of
two or more domains.
• The core of a domain is built from combinations of supersecondary
structural elements (motifs)
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26. Quaternary structure
• Quaternary means four.
• Quaternary protein is the arrangement of multiple folded protein or coiling
protein molecule in a multi subunit complex.
• A variety of bonding interaction include H-bonding, salt bridges, & disulphide
bonds.
• E.g Hemoglobin
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29.  Classification of Protein
• Globular proteins
• Fibrous proteins
According to
structure
• Simple protein
• Conjugated protein
According to
composition
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According to
function

30. Classification according to Structure
a) Globular Protein
• Globular proteins or spheroproteins are spherical ("globe-like") proteins and
are one of the common protein .
• Globular proteins are somewhat water-soluble (forming colloids in water),
unlike the fibrous or membrane proteins.
• There are multiple fold classes of globular proteins, since there are many
different architectures that can fold into a roughly spherical shape.
EXAMPLES
Hemoglobin, myoglobin
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31. Structure of hemoglobin
• Hemoglobin is composed of four polypeptide chains: two α chains and
two β chains—held together by noncovalent interactions
• Quaternary structure of hemoglobin is composed of two identical dimers,
(αβ)1 and (αβ)2.
• The two polypeptide chains within each dimer are held tightly together
by hydrophobic interactions (both in the interior & on the surface).
• Ionic and hydrogen bonds also occur between the members of the dimer.
• Weak ionic interaction b/w dimers—position of dimers different in
deoxyhemoglobin & oxyhemoglobin
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32. T.form:
• The deoxy form of hemoglobin is
called the “T,” or taut
• the two αβ dimers interact through
a network of ionic bonds & H-
bonds
R.Form
• The oxygenated form of hemoglobin
is called the R.form (Relaxed form).
• The binding of oxygen to
hemoglobin causes the rupture of
some of the ionic bonds and H-
bonds b/w the αβ dimers
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33. Function of Hemoglobin
• Hemoglobin is found exclusively in red blood cells (RBCs), where
its main function is to transport oxygen (O2) from the lungs to the
capillaries of the tissues.
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34. b) Fibrous protein
• A Fibrous protein is a protein with an elongated shape. Fibrous
proteins provide structural support for cells and tissues.
• There are special types of helices present in two fibrous proteins α-
keratin and collagen.
• These proteins form long fibres that serve a structural role in the
human body.
Examples are,
I. Collagen
II. Elastin 34

35. Collagen
• Collagen is the most abundant protein in the human body
• A typical collagen molecule is a long, rigid structure in which three polypeptides (referred
to as “α chains”) are wound around one another in a rope-like triple helix.
• The three polypeptide α chains are held together by hydrogen bonds between the
chains.
• Each helix contain approximately 1,000 amino acids.
• Per turn contains 3 amino acid.
• α chains are combined to form the various types of collagen found in the tissues.
• Collagen is rich in proline and glycine.
• Collagen contains hydroxy - proline (hyp) and hydroxylysine (hyl), which are not present
in most other proteins
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36.  Structure of collagen
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37.  Types of Collagen
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38.  Formation of Collagen
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39. Elastin
• Elastin is a highly elastic protein in connective tissue that can stretch and bend
in any direction, giving connective tissue elasticity. .
• composed of elastin and glycoprotein microfibrils are found in the lungs, the
walls of large arteries, and elastic ligaments
• Elastin helps skin to return to its original position when it is poked or pinched.
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40.  Structure of Elastin
• linear polypeptide composed of about 700 amino acids (primarily nonpolar).
• rich in proline & lysine but little number of hydroxyproline and hydroxy lysine.
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43. Classification a/c to Composition
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44. Functional Classification of Protein.
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45. Any Questions ?
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