Biology: Protein
Classification
A brief tour throughout how proteins are
classified; structure-, shape-, and
function-wise.
Protein Classification
» Protein can be differentiated depending on their:
• Structure (Primary and Secondary structure)
• Shape (Globular and Fibrous proteins)
• Function (Enzymatic, Defensive, Storage, Transport,
Hormonal, Receptor, Contractile and Motor, and
Structural proteins)
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Protein classification – Structure
Classification of protein according to their structure
» Structure classification is divided into two parts:
• Primary structure
• Secondary structure
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Protein Classification – Structure – Primary
Classification of protein according to their primary structure
» The sequence of amino acid residues along the peptide
is called primary.
» It’s the structure of the peptide.
» It also include the determination of the number of amino
acid residues in a peptide chain.
» Primary structure of human insulin:
•
•
CHAIN 1: GIVEQ CCTSI CSLYQ LENYC N
CHAIN 2: FVNQH LCGSH LVEAL YLVCG ERGFF YTPKT
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Protein Classification – Structure – Secondary
Classification of protein according to their secondary structure
» Secondary structure may take one of the following
forms:
•
•
•
•
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Alpha – Helix
Beta Pleated Sheet
Loop or Coil Conformation
Super secondary motifs
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Protein Classification – Structure – Secondary (Continue)
Pictures of the possible secondary structures.
» Alpha(α)- Helix
» β- Pleated Sheath
» Loop or Coil Conformation
» Super secondary Motifs
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Protein Classification – Shape
Classification of protein according to their shape
» Proteins can be classified according to their shape into:
• Globular Protein
• Fibrous Protein
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Protein Classification – Shape (Continue)
Fibrous Proteins
Globular Proteins
» Their axial ratio more than 10.
» They are long thread like molecule.
» Their axial ratio less than 10.
» They are spheroid or ovoid in shape.
» Their helical strands mainly form fibers.
» Enzymes are mostly globular in shape.
» These protein are insoluble in water.
» They subdivided into two type of proteins:
» They form structure of the tissue.
• Albumins: Water soluble.
» They are present where support is required.
• Globulin: Soluble in dilute salt solution.
» Examples:
• Collagen
• Elastin
• Keratin
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Protein Classification - Function
» Proteins can be classified according to function into:
•
•
•
•
•
•
•
•
Enzymatic proteins
Defensive proteins
Storage proteins
Transport proteins
Hormonal proteins
Receptor proteins
Contractile and motor proteins
Structural proteins
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Protein Classification – Function – Enzymatic and Defensive proteins
Enzymatic proteins
Defensive proteins
» Function: Selective acceleration of chemical reactions.
» Function: Protection against disease.
» Example: Digestive enzymes catalyze the hydrolysis
of bonds in food molecules.
» Example: Antibodies inactive and help destroy viruses
and bacteria.
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Protein Classification – Function – Storage and Transport proteins
Storage Proteins
Transport proteins
» Function: Storage of amino acids.
» Function: Transport of substances.
» Examples: Casein, the protein of milk, is the major
source of amino acids for baby mammals. Plants have
storage proteins in their seeds. Ovalbumin is the
protein of egg white, used as an amino acid source for
the developing embryo.
» Examples: Hemoglobin, the iron-containing protein of
vertebrate blood, transports oxygen from the lungs to
other parts of the body. Other proteins transport
molecules across membranes, as shown in the picture
below.
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Protein Classification – Function – Hormonal and Receptor proteins
Hormonal Proteins
Receptor Proteins
» Function: Coordination of an organism‘s activities.
» Function: Response of cell to chemical stimuli.
» Example: Insulin, a hormone secreted by the pancreas,
causes other tissues to take up glucose, thus regulating
blood sugar concentration.
» Example: Receptors built into the membrane of a
nerve cell detect signaling molecules released by other
nerve cells.
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Protein Classification – Function – Contractile and Motor, and Structural proteins
Contractile and Motor Proteins
Structural Proteins
» Function: Movement.
» Function: Support.
» Examples: Motor proteins are responsible for the
shrinkage, widening, and twisting of cilia and flagella.
Actin and myosin proteins are responsible for the
contraction of muscles.
» Examples: Keratin is the protein of hair, horns,
feathers, and other skin appendages. Insects and
spiders use silk fibers to make their cocoons and webs,
respectively. Collagen and elastin proteins provide a
fibrous framework in animal connective tissues.
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Thank You
Fady Adel Kamal
Ahmed Mohammed Magdy
Abd El-Rahman Abd El-Nasser
Mahmoud Mohammed Gomaa