Diverse Macromolecules

V. proteins are macromolecules that are polymers formed from amino acids monomers A. proteins have great structural diversity and perform many roles B. roles include enzyme catalysis, defense, transport, structure/support, motion, regulation; protein structure determines protein function

C. proteins are polymers made of amino acid monomers linked together by peptide bonds 1.amino acids consist of a central or alpha carbon; bound to that carbon is a hydrogen atom, an amino group (-NH 2 ), a carboxyl group (-COOH), and a variable side group (R group) the R group determines the identity and much of the chemical properties of the amino acid

there are 20 amino acids that commonly occur in proteins; pay attention to what makes an R group polar, nonpolar, or ionic (charged) and thus their hydrophobic or hydrophilic nature

plants and bacteria can usually make their own amino acids; many animals must obtain some amino acids from their diet (essential amino acids )

2.the peptide bond joins the carboxyl group of one amino acid to the amino group of another; is formed by a condensation reaction 2.two amino acids fastened together by a peptide bond is called a dipeptide, several amino acids fastened together by peptide bonds are called a polypeptide

D. the sequence of amino acids determine the structure (and thus the properties) of a protein E. proteins have 4 levels of organization or structure 1.primary structure (1  ) of a protein is the sequence of amino acids in the peptide chain

2.secondary structure (2  ) of a protein results from hydrogen bonds involving the backbone, where the peptide chain is held in structures, either a coiled α-helix or folded β-pleated sheet; proteins often have both types of secondary structure in different regions of the chain

3. tertiary structure (3  ) of a protein is the overall folded shape of a single polypeptide chain, determined by secondary structure combined with interactions between

4.quaternary structure (4  ) of a protein results from interactions between two or more separate polypeptide chains the interactions are of the same type that produce 2  and 3  structure in a single polypeptide chain when present, 4  structure is the final three- dimensional structure of the protein (the protein conformation) example: hemoglobin has 4 polypeptide chains not all proteins have 4  structure

Tertiary Structure of Hemoglobin

5.ultimately the secondary, tertiary, and quaternary structures of a protein derive from its primary structure, but molecular chaperones may aid the folding process 6.protein conformation determines function

7.denaturation is unfolding of a protein, disrupting 2 , 3 , and 4  structure changes in temperature, pH, or exposure to various chemicals can cause denaturation denatured proteins typically cannot perform their normal biological function denaturation is generally irreversible

F. enzymes are biological substances that regulate the rates of the chemical reactions in living organisms; most enzymes are proteins (covered in some detail later in this course) G. “related compounds” –amino acids; modified amino acids; polypeptides too short to be considered true proteins; and modified short polypeptides