Protein StructureAmino Acids, PolypeptideLevels of Structure
Monomer The single unit that makes up a protein is an amino acid Question: Based on its name, which 2 functional groups would be found in an amino acid? An amino acid is sometimes referred to as a residue
Amino acid structure four components attached to a central carbon: amino group H carboxylic acid (carboxyl) group | hydrogen atom H2N – C – COOH | variable R group (or side chain) R Question: Determine which functional group is acidic and basic. Explain how you know.
Amino acid structure H Amphiprotic: containing both | acidic and basic functional groups H2N – C – COOH | The ionized form is observed in R aqueous solutions because the +H2O acidic group can donate H+ ion to H the basic group | +H N 3 – C – COO- | R
Amino acid R groups (side chains) differences in R groups produce the 20 different amino acids 8 are essential: body cannot synthesize them
Amino acid R groups (side chains) Physical and chemical characteristics of the R group determine the unique characteristics of an amino acid Amino acids are classified into 4 groups based on their R groups: Nonpolar H | Polar H2N – C – COOH Acidic | basic R
Activity Given the 20 amino acids, group them into the 4 categories based on the properties of their R groups The 4 categories are: Nonpolar Polar Acidic basic
Protein shape determines function Amino acid order determines the shape (conformation) of a protein Conformation determines function Function depends on its ability to recognize and bind a molecule Amino acids conformation function binding
Protein binding examples Antibodies bind to particular foreign substances that fit their binding sites. Enzymes recognize and bind to specific substrates, facilitating a chemical reaction. Neurotransmitters pass signals from one cell to another by binding to receptor sites on proteins in the receiving cell.
Levels of protein structure Primary (1o) organizes folding within Secondary (2o) a single polypeptide Tertiary (3o) interactions between two Quaternary (4o) or more polypeptides that make a protein
Tertiary (3o) Structure: Proline kink Proline is the only amino acid in which the R group is attached to the amino group Forms a natural kink in the polypeptide Helps to shape tertiary structure
Tutorial: Protein Folding http://www.wiley.com/legacy/college/boyer/0470003790/ani mations/protein_folding/protein_folding.htm
Conformational Change Changing the shape of a protein Reversible Does not disrupt a proteins function but rather is what defines the protein’s function Change occurs in response to the physical and chemical conditions.