Proteins & Enzymes

What are proteins? Large organic molecules Always contain nitrogen Essential to the structure and function of living things Made up of smaller units called ‘amino acids’ Amino Acid

Amino Acids Join together to form long chains know as proteins or polypeptides Order and number of amino acids in these chains determines the type of protein 20 identified amino acids in the human body

Sources of essential amino acids Non-essential: can by synthesized from other amino acids in the body Essential: cannot be manufactured by the body, must be present in food Sources of essential amino acids

Transport Proteins Found in the membrane of cells Control the movement of substances into and out of organelles and cells Channel proteins, a type of transport protein, act like gates to allow large compounds (e.g. – glucose) to move across membranes

Structural Proteins Link membranes, cytoplasm and the nucleus, allowing for communication Structural protein, collagen, is found in the bones, cartilage, tendons, ligaments, connective tissue and skin of humans

Enzymes Enzymes are one of the most important groups of proteins They speed up and control all chemical reactions within the body Generally specific enzymes act as catalysts for specific reactions

Types of enzymes Intracellular enzymes: occur inside cells, where they speed up and control metabolic reactions Extracellular enzymes: produced by cells, but catalyze reactions outside the cell (e.g. – digestion)

1. Enzymes generally work very rapidly Properties of enzymes 1. Enzymes generally work very rapidly One of the fastest enzymes is catalase Converts hydrogen peroxide into oxygen and water Accumulation of hydrogen peroxide can be toxic to the body

2. Enzymes are not destroyed or altered by the reactions they catalyze Properties of enzymes 2. Enzymes are not destroyed or altered by the reactions they catalyze This means they can be used again However, cannot be used forever, as there shape can be altered over time

Enzyme catalyses reaction Properties of enzymes 3. Enzymes can work in either direction, as metabolic reactions are generally reversible A + B Substrate C + D Products Enzyme catalyses reaction The reaction will go in either direction until an equilibrium between the substrate and products is reached NOTE: Substrate: substances that enter a reaction Products: substances at the end of the reaction

Properties of enzymes 4. Enzymes are affected by temperature and have an optimal range at which they operate Below optimal range, they do not function efficiently Above this range, they are denatured – enzyme changes shape and can no longer function efficiently Optimal range varies between organisms (mammals: 35-40*C)

5. Enzymes are sensitive to pH Properties of enzymes 5. Enzymes are sensitive to pH Most intracellular enzymes function at their best around neutral (pH 7) An excessively acidic (below pH 7) or basic (above pH 7) denatures the enzyme However, digestive enzymes behave differently ‘Pepsin’ functions better in acidic environment ‘Trypsin’ functions better in a basic environments

6. Enzymes are usually specific to particular reactions Properties of enzymes 6. Enzymes are usually specific to particular reactions Generally, one enzyme will only catalyze one type of reaction Extracellular enzymes can work on a variety of substrates

Enzyme-substrate complex enzyme + substrate(s) When an enzyme controlled reaction takes place, the enzyme and substrate join briefly to form an enzyme-substrate complex Substrate molecules then react together and the end product leaves the enzyme enzyme-substrate complex enzyme + end product(s)

Lock-and-key mechanism Is thought that each enzyme has a precise place (‘active site’) to which its substrate molecules becomes attached Recent research questions this theory

Induced-fit hypothesis New theory suggests that when a substrate combines with an enzyme, the enzyme changes shape slightly to fit the substrate into the active site