Amino acid and proteins

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Amino acid and proteins
Ghollam-Reza Moshtaghi-Kashanian Biochemistry
Department Medical School Kerman University of
Medical sciences
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Classification of Bio-Molecules

• Proteins
• Wide range of roles
• Within the cell
• Enzymes
• Structural
• Gene activators / suppressors
• Membrane receptors / transporters
• Contractile elements

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• Proteins
• Wide range of roles
• Outside of the cell
• Enzymes
• Structural
• Hormones
• Antibodies
• Toxins
• Transporters
• (Membrane receptors / transporters)

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• Proteins
• How do they accomplish so many functions?
• A multitude of shapes
• Interact selectively with other molecules
• High specificity

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• Proteins
• Structure
• Polymers of amino acid (aa) monomers
• Two aspects of aa structure
• Shared properties
• Properties unique to each aa

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• Proteins
• Amino Acids Shared properties
• A carboxyl and an amino group separated by a
  carbon atom the a carbon.
• At physiological pH the a carboxyl looses a
  proton and the amino group accepts a proton

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• Proteins
• Amino Acids Shared properties
• During protein synthesis each amino acid is
  linked to the next via a peptide bond forming a
  polypeptide
• A peptide bond results from the linkage of the
  carboxyl group of one amino acid to the amine
  group of its neighbor, with the elimination of a
  molecule of water

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• Proteins
• Amino Acids Unique properties
• The side chain group or R group 20 forms
• R group properties provide the basis of the
  diverse structure and activities of proteins.

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• Amino Acids Unique properties
• The side chain group or R group 20 forms

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• Amino Acids Unique properties
• The side chain group or R group 20 forms

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• Proteins
• Structure
• Description at several levels of organization
• Primary, secondary, tertiary, quaternary

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• Proteins
• Structure
• Primary
• aa sequence
• Possible variations x 20n, where n the no.
  aa in the polypeptide
• If n 10
• X 1013
• If n 20
• X 1026

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• Proteins
• Structure
• Secondary
• Conformation of specific regions
• Two specific types
• Alpha helix
• Beta-pleated sheet composed of b strands
• Portions not organized into an a helix or a b
  sheet consist of turns, hinges, loops or
  finger-like extensions

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• Proteins
• Structure
• Secondary
• In pictorial representations a helices are shown
  as helical ribbons and b strands as flattened
  arrows

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• Proteins
• Structure
• Tertiary
• The conformation of the entire protein

Leptin
Ribonuclease
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• Proteins
• Structure
• Quaternary
• Multiples of single polypeptides linked together
• Each polypeptide is termed a subunit
• May be linked by
• Covalent disulfide bridges
• Non-covalent between hydrophobic patches
• In two-polypeptide proteins
• if the subunits are identical it is a homodimer
• If the subunits are different it is a
  heterodimer

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• Proteins
• Structure
• Dynamic changes within proteins
• Protein structure is not rigid or inflexible
• Capable of considerable internal movements
• Some random and small-scale
• Predictable changes triggered by interaction with
  another molecule are conformational changes
• Complexes of proteins form and break
• Association and Dissociation
• Interacting proteins have complementary surfaces
• As they come into close contact their interaction
  is stabilized by non-covalent bonds