The document discusses the structure of proteins from primary to quaternary structure. It defines proteins as polymers of amino acids linked by peptide bonds. There are four levels of protein structure: primary structure refers to the amino acid sequence; secondary structure involves hydrogen bonding of alpha helices and beta sheets; tertiary structure describes the overall 3D shape from interactions between R groups; and quaternary structure involves the aggregation of multiple polypeptide subunits, as seen in hemoglobin. Understanding protein structure is crucial to explaining their diverse functions.
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Introduction to protein structure
1. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Introduction to protein structure
Bilal El Houdaigui
National School of Applied Science of Tangier
bilal.elhoudaigui@gmail.com
September 22, 2016
3. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Importance of protein structure
Proteins are the building blocks of all cells.
In the world of proteins:
Structure ≡ Function!
DNA encodes life..Yes! But proteins carry
out life processes, replication,
reproduction, defense etc!
4. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Protein
Protein
Proteins are large macromolecules, consisting of one or more
long chains of amino acid residues.
Figure 1: A representation of the 3D structure of the protein
myoglobin
5. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Amino Acide Structure (1/2)
Definition
Amino acids are biologically important organic compounds
containing amine (-NH2) and carboxylic acid (-COOH)
functional groups, usually along with a side-chain (R group)
specific to each amino acid.
The key elements
of an amino acid
are :
Carbon
Hydrogen
Oxygen
Nitrogen
Figure 2: The structure of an amino acid
7. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Peptide
Peptide
Peptides are biologically occurring short chains of amino acid
linked by peptide bonds.
Figure 4: Tetrapeptide structural formulae
Polypeptide is a long, continuous, and unbranched
peptide chain.
8. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Peptide bond
Peptide bond
A peptide bond is a covalent chemical bond linking two
consecutive amino acid along a peptide or protein chain.
Figure 5: Peptid formation
9. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Covalent bond
Covalent bond
A covalent bond, also called a molecular bond, is a chemical
bond that involves the sharing of electron pairs between atoms.
Figure 6: Covalent bond - hydrogen
10. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Primary structure : Definition
Definition
The primary structure of a protein refers to the linear sequence
of amino acids in the polypeptide chain. The primary structure
is held together by covalent bonds such as peptide bonds.
Figure 7: Primary protein structure (a)
11. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Primary structure : Characteristics
Characteristics
Unique sequence of amino
acid.
Sequence determined by
DNA.
Amino acids are covalently
linked by peptide bonds.
By convention, the
structure of a protein
starts from the
amino-terminal (N) end
and ends in the
carboxyl-terminal (C) end.
Figure 8: Primary protein structure
(b)
12. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Secondary structure : Characteristics & Types
Characteristics
Results from hydrogen bonds at regular intervals along the
polypeptide backbone.
Not found in all proteins.
Two major Types of secondary structure:
1 α-helix.
2 β sheet.
13. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Secondary structure : Alpha Helix
Characteristics of the
alpha-Helix structure:
Spiral structure.
Tightly packed, coiled
polypeptide backbone
core.
Side chain extend
outwards.
Stabilized by H bonding
b/w carbonyl oxygen and
amide hydrogen.
The helix has 3.6 residues
per turn. Figure 9: Alpha Helix
14. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Secondary structure : Beta sheet
Characteristics of the beta sheet
structure:
Each β strand is fully extended.
Stabilized by H bonding b/w
carbonyl oxygen and amide
hydrogen the of adjacent chains.
Types of the beta sheet:
Parallel β sheet.
Antiparallel β sheet.
Figure 10: Beta sheet
15. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Tertiary structure : Characteristics
Characteristics
Tertiary structure is the three
dimensional conformation of a
polypeptide.
The common features of
protein tertiary structure reveal
much about the biological
functions of the proteins and
their evolutionary origins.
The function of a protein
depends on its tertiary
structure. If this is disrupted,
it loses its activity.
Figure 11: Tertiary structure
16. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Tertiary structure : Interactions
Interactions between:
R groups and R groups.
R groups and backbone.
Types of interaction:
Hydrogen bonds
Ionic bonds.
Hydrophobic interactions
(Often in interior of
protein)
Covalent bonds
(Disulfide bridge: formed
between the sulfhydryl
groups (SH) of cysteine
amino acids).
Figure 12: interactions in tertiary
structure
17. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Quaternary structure : Characteristics
Characteristics
Aggregation of two or more polypeptide subunits.
Not found in all proteins.
Hemoglobin (Example):
Hemoglobin is a protein that
exist in the red blood cells.
It carries oxygen from the
respiratory organs to the rest of
the body.
Figure 13: Structure of human
hemoglobin
19. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Conclusion
Proteins are extraordinarily complex molecules. Of all the
molecules encountered in living organisms, proteins have
the most diverse functions.
So a basic understanding of the structure of proteins is
necessary to comprehend its role in organisms.
Further researches will provide more insight into the
structure of several other proteins in the coming year.
20. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
The End
22. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
Disulfide bond
Definition
A disulfide bond, also called an S-S bond, or disulfide
bridge, is a covalent bond derived from two thiol groups. In
biochemistry, the terminology R-S-S-R connectivity is
commonly used to describe the overall linkages.
Figure 14: Formal depiction of disulfide bond formation as an
oxidation
23. Structure of
proteins
Introduction
Why ?
Some definitions
Primary
structure
Definition
Characteristics
Secondary
structure
Characteristics
& Types
Alpha Helix
Beta sheet
Tertiary
structure
Characteristics
Interactions
Quaternary
structure
Characteristics
Recap
Conclusion
What Is the Difference Between a Peptide and a
Protein?
Peptide VS Protein
The basic distinguishing factors are size and structure.
Peptides are smaller than proteins. Traditionally, peptides
are defined as molecules that consist of between 2 and 50
amino acids, whereas proteins are made up of 50 or more
amino acids. In addition, peptides tend to be less well
defined in structure than proteins, which can adopt
complex conformations known as secondary, tertiary, and
quaternary structures.
Figure 15: Protein, Peptide and Amino Acid
