7.5 Proteins

Four levels of protein structure and their significance

Primary structure: sequence of amino acids attached by peptide linkage.

Secondary structure: parts of polypeptide chain take up particular shape; alpha helix, beta pleated sheet.

Tertiary structure: molecule is farther folded in held in particular complex shape, 3D shape due to interaction of R groups + surrounding medium.

Quaternary structure: 2 or more proteins become held together forming a complex biologically active molecule - like hemoglobin.

Structures of protein (biologyexams4u.com)

Difference between fibrous and globular proteins

Fibrous: protein elongated shapes, insoluble in water and physically tough.

Examples: keratin, collagen.

Globular: compact and rounded and water soluble.

Examples: enzymes, antibodies.

Significance of polar and non-polar amino acids

Polar amino acids have hydrophilic R groups; non-polar amino acids have hydrophobic R groups.

Water soluble proteins, non-polar amino acids found in center of protein (stabilizing structure) while polar amino acids found on surface (interacting with water molecules).

Membrane bound proteins - non-polar amino acids tend to be localized on surface in contact with membrane, polar amino acids line interior pores (to create hydrophilic channels).

Enzymes - active site depends on location and distribution of polar/non-polar amino acids as hydrophobic/hydrophilic interactions play role in substrate binding to active site.

Four functions of protein

Collagen (fibrous) - protein strengthening tissues.

Insulin (Globular) - hormone involved in regulation of blood sugar.

Sucrase (Globular) - enzyme that breaks down sucrose into glucose/fructose.

Immunoglobulins (Globular) involved in defense against disease.