Proteins are involved in Proteins are essential to the structures and activities of life Proteins are involved in structure movement defense transport communication storage regulation of chemical reactions ENZYMES!! Structural proteins Support: Silk from spiders, hair of mammals, fibers that make up tendons and ligaments Contractile proteins Provide muscular movement. Ex. actin/myosin Storage proteins- storage of amino acid. Ex. casein, the protein of milk, stores amino acids for baby mammals. Defensive proteins Protection against disease. Antibodies combat bacteria and viruses. Transport proteins Transport of other substances. Hemoglobin Signal proteins Coordination of organism’s activities: Insulin, a hormone, helps regulate the concentration of sugar in the blood of vertebrates. Enzymes Serves as chemical catalyst (changes the rate of a reaction) Promote and regulate virtually all chemical reactions in the cell Mammalian hair is composed of structural proteins

Their diversity is based on different arrangements of amino acids Proteins are the most structurally and functionally diverse of life’s molecules Their diversity is based on different arrangements of amino acids The key to variation is the sequence in which the monomers are strung together.

20 Amino Acids used in Human Proteins

Each amino acid contains: an alpha (α) carbon a hydrogen an amino group a carboxyl group an R group, which distinguishes each of the 20 different amino acids Figure 3.12A By having 20 amino acids, the monomers can join together in different combinations and create a wide variation of differing proteins.

Each amino acid has specific properties Note the functional groups present. Some are nonpolar, polar, acidic and basic. Leucine (Leu) Serine (Ser) Cysteine (Cys) HYDROPHOBIC HYDROPHILIC Figure 3.12B

Amino acids can be linked by peptide bonds Cells link amino acids together by dehydration synthesis The resulting covalent linkage is called a peptide bond Product is called a dipeptide (2 amino acids)

Glycine: Dehydration Synthesis

Amino acids can be linked by peptide bonds Cells link amino acids together by dehydration synthesis The bonds between amino acid monomers are called peptide bonds Carboxyl group Amino group PEPTIDE BOND The resulting covalent linkage is called a peptide bond Product is called a dipeptide (2 amino acids) Dehydration synthesis Amino acid Amino acid Dipeptide

Polypeptide Chains Molecules formed by strings of hundreds of amino acids linked together by peptide bonds Chain of amino acids = polypeptide Range in length from a few monomers to a thousand or more Peptide bond Peptide bond Peptide bond Peptide bond Peptide bond Peptide bond

A protein’s specific shape determines its function! A protein consists of polypeptide chain(s) folded into a unique 3-D shape = tertiary structure The shape determines the protein’s function A protein loses its specific function when its polypeptide(s ) unravels = denaturation =  Each polypeptide has a unique sequence of amino acids and assumes a unique 3-D shape in a protein Nearly all proteins must recognize and bind to some other molecule in order to function. Therefore their shape matters! The function of each protein is a consequence of its specific shape, which is lost when a protein denatures. The function of each protein is a consequence of its specific shape During denaturation, polypeptide chains unravel, losing their specific shape and as a result, their function. Denaturation may be causes by high temperatures or various chemical treatments. Example: egg white cooking Figure 3.14B

A protein’s primary structure is its amino acid sequence For proteins to perform its specific function, it must have the correct collection of amino acids arranged in a precise order. Primary structure is the sequence of amino acids forming its polypeptide chains For proteins to perform its specific function, it must have the correct collection of amino acids arranged in a precise order. Even a slight change in a protein’s primary structure may affect its overall shape and its ability to function For example, a single amino acid change in hemoglobin (O2 carrying blood protein) causes sickle-cell disease Figure 3.15, 16

A protein’s primary structure is its amino acid sequence The substitution of one amino acid for another at a particular position in hemoglobin causes sickle cell disease Normal red blood cells are disk-shaped, but in sickle-cell disease, the abnormal hemoglobin molecules tend to crystallize, deforming some of the cells into a sickle shape. Causes sickle cell crises which occur when the angular cells clog tiny blood vessels, impeding blood flow.

A protein’s primary structure is its amino acid sequence Secondary structure is polypeptide coiling or folding produced by hydrogen bonding Primary structure Amino acid Primary structure is the sequence of amino acids forming its polypeptide chains For proteins to perform its specific function, it must have the correct collection of amino acids arranged in a precise order. Secondary structure Secondary structure: polypeptide coil or folds into local patterns Coiling of a polypeptide chain results in an alpha helix Folding of the polypeptide chain results in a pleated sheet. Coiling and folds maintain the hydrogen bonds Secondary structure Hydrogen bond Pleated sheet Alpha helix

Secondary structure is polypeptide coiling or folding produced by hydrogen bonding Both the oxygen and nitrogen atoms of the backbone are electronegative, with partial negative charges. The weakly positive hydrogen atom attached to the nitrogen atoms has an affinity for the oxygen atoms of a nearby peptide bond. A helix: delicate coil held together by hydrogen bonding between every 4th amino acid. B pleated: two or more regions of polypeptide chain lie parallel to eachother. Hydrogen bonds hold structure together.

Tertiary structure is the overall 3-D shape of a polypeptide Polypeptide (single subunit of transthyretin) Tertiary structure refers to the overall, 3-D shape of a polypeptide. Contains both alpha helix and pleated sheet regions This particular arrangement of coils and folds give the polypeptide the specific shape appropriate to its function Hydrophobic side chains usually end up in the interior of the protein, away from water. Hydrogen bonds between polar side chains and ionic bonds between positively and negatively charged side chains help stabilize tertiary structure. Reinforced by strong, covalent bond called disulfide bridges. Disulfide bridges form when amino acids with sulfhydral groups (-SH) are brought close together by the folding of the protien. Quartenary structure Many proteins consist of 2 or more polypeptide chains or subunits Figure 3.17, 18

Tertiary structure is the overall shape of a polypeptide Hydrophobic side chains usually end up in the interior of the protein, away from water. Hydrogen bonds between polar side chains and ionic bonds between positively and negatively charged side chains help stabilize tertiary structure. Reinforced by strong, covalent bond called disulfide bridges. Disulfide bridges form when amino acids with sulfhydral groups (-SH) are brought close together by the folding of the protien.

Tertiary structure is the overall 3-D shape of a polypeptide Quaternary structure is the relationship among multiple polypeptides of a protein Tertiary structure Polypeptide (single subunit of transthyretin) Tertiary structure refers to the overall, 3-D shape of a polypeptide. Contains both alpha helix and pleated sheet regions This particular arrangement of coils and folds give the polypeptide the specific shape appropriate to its function Hydrophobic side chains usually end up in the interior of the protein, away from water. Hydrogen bonds between polar side chains and ionic bonds between positively and negatively charged side chains help stabilize tertiary structure. Reinforced by strong, covalent bond called disulfide bridges. Disulfide bridges form when amino acids with sulfhydral groups (-SH) are brought close together by the folding of the protien. Quartenary structure Many proteins consist of 2 or more polypeptide chains or subunits Quaternary structure protein, with four identical polypeptide subunits Figure 3.17, 18

Quaternary structure is the relationship among multiple polypeptides of a protein Many (but not all) proteins consist of more than one primary chain. Quaternary bonding is largely by polar and hydrophobic interaction. Collagen- fibrous protein consisting of 3 helical polypeptides that are supercoiled to form a ropelike structure of great strength. Accounts for 40% of the protein in the human body, collagen strengthens connective tissues throughout the body. (connective tissue in skin, bone, tendons, ligaments) Hemoglobin: Another good example of a protein with quaternary structure is hemoglobin: 4 polypeptide subunits, two of one kind (a chain) and two of another kind (b chains). Each subunit has a nonpolypeptide unit called a heme, with an iron atom that binds to oxygen. Transthyretin, with four identical polypeptide subunits Four Levels