Proteins

Protein Proteins are polymers of molecules called amino acids.

Protein Proteins perform many varied functions: controlling the rate of reactions regulating cell processes

Protein Other functions: forming cellular structures transporting substances into or out of cells helping to fight disease.

Structure and Function Amino acids differ from each other in a side chain called the R-group, which have a range of different properties. More than 20 different amino acids are found in nature. This variety results in proteins being among the most diverse macromolecules.

Levels of Organization Proteins have four levels of structure. A protein’s primary structure is the sequence of its amino acids. Secondary structure is the folding or coiling of the polypeptide chain.

Levels of Organization Tertiary structure is the complete, three-dimensional arrangement of a polypeptide chain. Proteins with more than one chain have a fourth level of structure, which describes the way in which the different polypeptide chains are arranged with respect to each other. For example, the protein shown, hemoglobin, consists of four subunits.

Proteins in the Diet Proteins supply raw materials for growth and repair of structures such as skin and muscle.

Proteins in the Diet The body is able to synthesize only 12 of the 20 amino acids used to make proteins. The other eight are called essential amino acids and must be obtained from the foods that you eat.

Proteins Meat, fish, eggs, and milk generally contain all eight essential amino acids. Foods derived from plants, such as grains and beans, do not.

Proteins Many enzymes are made of proteins.

Enzymes Enzymes speed up chemical reactions that take place in cells. Catalysts – substance that speeds up the rate of chemical reactions Enzymes = Catalysts

Nature’s Catalyst Enzymes are proteins that act as biological catalysts. They speed up chemical reactions that take place in cells. Enzymes act by lowering the activation energies, which has a dramatic effect on how quickly reactions are completed.

Enzyme-Substrate Complex The reactants of enzyme-catalyzed reactions are known as substrates. For example, the enzyme carbonic anhydrase converts the substrates carbon dioxide and water into carbonic acid (H 2 CO 3 ).

Enzyme-Substrate Complex The substrates bind to a site on the enzyme called the active site. The active site and the substrates have complementary shapes. The fit is so precise that the active site and substrates are often compared to a lock and key.

Regulation of Enzyme Activity Enzymes work best under ideal conditions. Temperature, pH, and regulatory molecules are all factors that can affect the activity of enzymes.

Regulation of Enzyme Activity Enzymes produced by human cells generally work best at temperatures close to 37°C, the normal temperature of the human body. Enzymes work best at certain pH values. For example, the stomach enzyme pepsin, which begins protein digestion, works best under acidic conditions.

Regulation of Enzyme Activity Human homeostasis is very important for the proper functioning of the body’s enzymes!