Proteins

Proteins • •

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Protein string of aminoacids. String folds in an intricate 3D structure which is unique to each proteins. Subunit of protein is aminoacid Aminoacid is composed of Central C atom (α C) An amino group (NH2)

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A hydrogen atom(H) A carboxyl group (COOH) A side chain (R)

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Polypeptide • • • •

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Polypepeptide: polypeptide is a chain of aminoacid residues linked together by peptide bonds (C-N) Structure of protein: Primary structure: Linear array of aminoacid in a polypeptide Secondary structure: Folding of localized parts of a polypeptide chain. Interaction of R groups-twist n fold in a specific way. stabilized by hydrogen bonds Two types of sec. structure: α helix: linear polypeptide twist around a cylinder.flexible. Eg. Structural protein β sheet: chain of a.acid fold back and forth upon itself instead of forming helix, regidity, eg. enzymes

Structure of protein •

Tertiary structure: packing of α helices and β sheets and random coils with the respect to each other on forming one whole polypeptide chain. Stabilized by hydrophobic interactions between polar and non polar side chain. Interaction hold the α helices and β sheets together • Quarternary structure: only exist if there is more than one polypeptide chain present in a complex protein.