Proteins Structure and Function PROTEINS Proteins are essential to the structures and activities of life... Protein Functions The seven major functions of protein are 1)Structural: 2)Contractile: 3)Storage: 4)Defense: 5)Transport: 6)Signaling: 7)Enzymes: Amino acids Monomeric subunit of polypeptides (proteins). Protein diversity is based on different arrangements of a common set of 20 amino acid monomers 20 natural amino acids .. .. The structure of the R group determines the specific properties of each amino acid Properties defined by R-group include: .. .. .. Essential Amino Acids. proteins = Cells link amino acids together by dehydration synthesis. Dipeptides are two amino acids long; polypeptides are from several to more than a thousand amino acids long Amino acid Dipeptide Amino acid Peptide bond Dehydration reaction Amino group Carboxyl group Synthesis of Polypeptides. Chain grows from amino terminus to carboxy terminus. R groups frequently interact with others A protein's specific shape determines its function. This unique folding gives each protein their specific function. A protein consists of one or more polypeptide chains spontaneously folded into a unique shape. LE 3-13 Groove A protein's shape depends on four levels of structure Primary structure Secondary structure Tertiary structure Quaternary structure Primary Structure. amino acids linked by the peptide bond. Are often similar among proteins of similar function Usually written from amino terminus to carboxy terminus Secondary Structure.. helix-stabilized by frequent polar groups -pleated sheets are formed by consecutive polar groups on two regions of polypeptide repetitive or regular folding patterns Tertiary Structure. 3 Dimension shape emerges Due to R group Interactions Hydrophobic interactions Nonpolar regions generally internalize in structure Disulfide bridge Very stable bond formed between two distant cysteine residues Ionic interactions Strong bond between oppositely charged side groups -Hydrogen bonds form between polar groups Quaternary Structure. Interactions are maintained between polypeptide chains by bonds similar to tertiary structure H-bonds, ionic interactions, hydrophobic interactions and disulphide bridges Protein Structure Revisited How many levels of protein folding are present in this image? Source: Collagen is an example of a protein with a quaternary structure Three subunits wound into a helix Structure provides great strength to long fibers Factors Affecting Folding Folding is influenced by environmental conditions .. .. .. Some proteins have more than one folding pattern (conformation) depending on the environment Many proteins undergo a conformational change when a substrate binds. Conformational changes are usually reversible. Denaturation.. Denatured proteins may refold if the conditions are appropriate. Chapperones promote or stabilise a proteins folding Proteins when heated can unfold or "Denature". This loss of three dimensional shape will usually be accompanied by a loss of the proteins function. If the denatured protein is allowed to cool it will usually refold back into its original conformation.