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Terms in this set (71)

• The primary structure of a protein is its unique sequence of amino acids.
Lysozyme, an enzyme that attacks bacteria, consists of 129 amino acids.
The precise primary structure of a protein is determined by inherited genetic information.
• Even a slight change in primary structure can affect a protein's conformation and ability to function.
The substitution of one amino acid (valine) for the normal one (glutamic acid) at a particular position in the primary structure of hemoglobin, the protein that carries oxygen in red blood cells, can cause sickle-cell disease, an inherited blood disorder.
The abnormal hemoglobins crystallize, deforming the red blood cells into a sickle shape and clogging capillaries.
• Most proteins have segments of their polypeptide chains repeatedly coiled or folded.
• These coils and folds are referred to as secondary structure and result from hydrogen bonds between the repeating constituents of the polypeptide backbone.
The weakly positive hydrogen atom attached to the nitrogen atom has an affinity for the oxygen atom of a nearby peptide bond.
Each hydrogen bond is weak, but the sum of many hydrogen bonds stabilizes the structure of part of the protein.
• Typical secondary structures are coils (an alpha helix) or folds (beta pleated sheets).
• The structural properties of silk are due to beta pleated sheets.
The presence of so many hydrogen bonds makes each silk fiber stronger than a steel strand of the same weight.
• Tertiary structure is determined by interactions among various R groups.
These interactions include hydrogen bonds between polar and/or charged areas, ionic bonds between charged R groups, and hydrophobic interactions and van der Waals interactions among hydrophobic R groups.
While these three interactions are relatively weak, strong covalent bonds called disulfide bridges that form between the sulfhydryl groups (SH) of two cysteine monomers act to rivet parts of the protein together.
• Quaternary structure results from the aggregation of two or more polypeptide subunits.
Collagen is a fibrous protein of three polypeptides that are supercoiled like a rope.
This provides structural strength for collagen's role in connective tissue.
Hemoglobin is a globular protein with quaternary structure.
It consists of four polypeptide subunits: two alpha and two beta chains.
Both types of subunits consist primarily of alpha-helical secondary structure.
Each subunit has a nonpeptide heme component with an iron atom that binds oxygen.