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Amino acid and proteins

Ghollam-Reza Moshtaghi-KashanianGhollam-Reza Moshtaghi-KashanianBiochemistry DepartmentBiochemistry DepartmentMedical SchoolMedical SchoolKerman University of Medical sciencesKerman University of Medical sciences

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Classification of Bio-Molecules

ProteinsWide range of roles

Within the cellEnzymes

Structural

Gene activators / suppressors

Membrane receptors / transporters

Contractile elements

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ProteinsWide range of roles

Outside of the cellEnzymes

Structural

Hormones

Antibodies

Toxins

Transporters

(Membrane receptors / transporters)

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ProteinsHow do they accomplish so many functions?

A multitude of shapesInteract selectively with other molecules

High specificity

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ProteinsStructure

Polymers of amino acid () monomers

Two aspects of structureShared properties

Properties unique to each

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ProteinsAmino Acids – Shared properties

A carboxyl and an amino group separated by a carbon atom – the carbon.

At physiological pH the carboxyl looses a proton and the amino group accepts a proton

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ProteinsAmino 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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ProteinsAmino 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 propertiesThe side chain group or R group – 20 forms

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Amino Acids – Unique propertiesThe side chain group or R group – 20 forms

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ProteinsStructure

Description at several levels of organizationPrimary, secondary, tertiary, quaternary

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ProteinsStructure

Primary sequence

Possible variations x = 20n, where n = the no. in the polypeptide

If n = 10

X = 1013

If n = 20

X = 1026

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ProteinsStructure

SecondaryConformation of specific regions

Two specific types

Alpha helix

Beta-pleated sheet – composed of strands

Portions not organized into an helix or a sheet consist of turns, hinges, loops or finger-like extensions

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ProteinsStructure

SecondaryIn pictorial representations helices are shown as helical ribbons and strands as flattened arrows

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ProteinsStructure

TertiaryThe conformation of the entire protein

Ribonuclease

Leptin

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ProteinsStructure

QuaternaryMultiples 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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ProteinsStructure

Dynamic changes within proteinsProtein 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 breakAssociation and Dissociation

Interacting proteins have complementary surfaces

As they come into close contact their interaction is stabilized by non-covalent bonds