Biochem

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amino acid

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an organic molecule that serves as the building block of proteins. Each amino acid contains:

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protein

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a large, complex molecule made up of one or more long chains of amino acids linked together by peptide bonds.

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Peptide Bond

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a covalent bond that links two amino acids together.

It forms between the carboxyl group (–COOH) of one amino acid and the amino group (–NH₂) of another, with the release of a water molecule — a type of dehydration (condensation) reaction.

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disulfide bond (bridge)

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a covalent bond formed between the sulfur atoms of two cysteine amino acids.

It helps stabilize the tertiary or quaternary structure of proteins.

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hydrophobic (attraction)

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the tendency of nonpolar (water-fearing) molecules or parts of molecules to cluster together and avoid contact with water.

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electrostatic attraction (salt bridge)

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a non-covalent interaction (electrostatic attraction) between oppositely charged side chains of amino acids

typically between a positively charged basic group and a negatively charged acidic group.

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α helix

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a common secondary structure in proteins, formed when the polypeptide chain coils into a right-handed spiral.

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β pleated sheet

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a type of secondary protein structure formed when segments of the polypeptide chain align side-by-side, creating a sheet-like arrangement stabilized by hydrogen bonds between backbone atoms.

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isoelectric point pI or pHi)

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the pH at which the molecule has no net electric charge — meaning the positive and negative charges balance out.

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zwitterion

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a molecule that contains both a positive charge and a negative charge, but the overall molecule is neutral