Proteins

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Proteins

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Compose 10-30% of cell mass and is the basic structural material of the body. Contain C, O, H, and Nitrogen.

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Amino Acids

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The building blocks of proteins

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Two important functional groups

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An amine group (-NH2) and an organic acid group (-COOH)

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How are proteins constructed?

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They are long chains of amino acids joined together by dehydration synthesis, with the amine end of one amino acid linked to the acid of the next. This is a peptide bond.

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Structural Levels of Proteins

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Primary, secondary, tertiary, and quaternary.

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Primary structure

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The linear sequence of amion acids composing the polypeptide chain. It is the backbone of the protein molecule.

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Secondary structure

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Twists or bends formed by coiling of the primary structure.

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Alpha-helix

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Resembles a telephone coil. It is stabalized by hydrogen bonds formed between NH and CO groups in amion acids in primary chain.

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Beta-pleated sheet

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The primary chains do not coil, rather they are linked side by side by hydrogen bonds to form a pleated, ribbon like structure that resembles an accordion.

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Tertiary structure

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Achieved when alpha and beta regions of the polypetpide chain fold upon one another to produce a compact ball-like molecule that is maintained by both covalent and hydrogen bonds.

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Quaternary structure

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Two or more polypeptide chains aggregate in a regular manner to form a complex protein. (Hemoglobin)

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Fibrous proteins

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Extended and strandlike; many exhibit only secondary strucutre, but some have quaternary. Insoluble in water and very stable. Examples: collagen, keratin, elastin

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Globular proteins

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Compact, spherical proteins that have at least tertiary strucutre; some have quaternary. Water soluble, chemically active molecules, and play crucial roles in virtually all biological processes. Examples: antibodies, hormones, enzymes

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Protein denaturation

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Hydrogen bonds breaking when the pH or the temp. rises above normal levels, causing proteins to unfold and lose their specific shape. Disruption is reversible in most cases. Sometimes irreversibly denatured (egg whites)