From: Protein Data Bank PDB ID: 1B0E Kalus, W., Zweckstetter, M., Renner, C., Sanchez, Y., Georgescu, J., Grol, M., Demuth, D., Schumacher, R., Dony, C., Lang, K., Holak, T. A.: structure of the IGF-binding domain of the insulin-like growth factor-binding protein-5 (IGFBP-5): implications for IGF and IGF-I receptor interactions. EMBO J 17 pp (1998)

 Diverse functions related to structure  Structural components of cells  Motor proteins  Enzymes  Antibodies  Hormones  Hemoglobin/myoglobin  Transport proteins in blood

 Amino acids  Amino group (NH 2 )  Carboxyl group (COOH)

 20 amino acids make up protein  8 essential amino acids (must be eaten in diet)  9 in infant (histidine)

 5 bonds or forces determine structure  Peptide bond  Hydrogen bond  Disulfide bond  Ionic bond  Hydrophobic force

 Peptide bond joins amino acids  Bond at both ends  Increases range of possible proteins  1.0 x peptides can be formed from 20 amino acids

 Linear sequence of amino acids forms primary structure (long chain of amino acids)  Sequence essential for proper physiological function

 Replacement of a single glutamine amino acid with valine in one chain of hemoglobin alters the structure and function of the protein

 Peptide chains fold into secondary structures to become more compact:   - helix   - pleated sheet

 Secondary structures fold and pack together to form tertiary structure  Usually globular shape  Tertiary structure stabilized by bonds between R groups (i.e. sidechains)

All amino acids contain a carboxyl group and an amino group. R-Groups distinguish between individual amino acids. R-Groups make them different from one another.

 Hydrogen bonds are weak electrical attractions between positively and negatively charged atoms of different molecules.

 Covalent bond between sulfur atoms on two cysteine amino acids

 Ions on R groups form bridges through ionic bonds  Ionic bonds form from the exchange of electrons between atoms  Example: NaCl (table salt)

 Close attraction of non-polar R groups in the chains  Very weak but collective interactions over large areas help stabilize the protein structure

 The arrangement of many tertiary structures into one large protein molecule  Not all proteins have or need a quaternary structure  Allows for changes in structure/function in response to chemical stimuli