Enzymes COPY

Enzymes are globular proteins that act as catalysts. they alter the rate of a chemical reaction without undergoing permanent changes themseves.

the sucrose water molecules must collide with sufficient energy to alter the arrangement of their atoms to form glucose and fructose the free energy of the products must be less than that of the substrates sucrose and water many reactions require an activation energy

there is an activaion energy level, like an energy barrier which must initially be overcome before the reaction can proceed

enzymes work by lowering this activation energy level in this way enzymes allow reactions to take place at lower temperature than normal this enables some metabolic processes to occur rapidly at the human body temperature of 37 degrees Celsius

these reactions would proceed too slowly to sustain life as we know it

active site

the active site is made up of a relatively small number of amino acids he active site forms a small depression within the much larger enzyme molecule

the substrate

fits neatly into this depression and forms an enzyme-substrate complex. the substrate molecule is held within the active site by bonds that temporarily form between certain amino acids of the active site and group of the substrate molecule

the induced fit model of enzyme action proposes that the active site forms as the enzyme and substrate interact the enzyme is flexible and can mould itself around the substrate the enzyme has a certain general shape but this alters in the presence of a substrate As it changes shape, the enzyme puts a strain on the substrate molecule. the strain distorts particular bonds in the substrate and consequently lowers the activation energy needed to break the bond

any change in an enzymes environment is likely to change its shape. the very act of colliding with its substrate is a change in its environment and so its shape changes- induced fit

Substrates collide with the enzyme’s active site and this must happen at the correct orientation and speed in order for a reaction to occur An enzyme-substrate complex forms when an enzyme and its substrate join together The enzyme-substrate complex is only formed temporarily before the enzyme catalyzes the reaction and the product(s) are released

The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s)

The shape of the active site (and therefore the specificity of the enzyme) is determined by the complex tertiary structure of the protein that makes up the enzyme

an enzyme-substrate complex

Enzyme reactions can either be catabolic or anabolic

Catabolic reactions involve the breakdown of complex molecules into simpler products, which happens when a single substrate is drawn into the active site and broken apart into two or more distinct molecules (products)

cellular respiration and hydrolysis

Anabolic reactions involve the building of more complex molecules from simpler ones by drawing two or more substrates into the active site, forming bonds between them and releasing a single product

protein synthesis photosynthesis

globular proteins

Enzymes can be intracellular or extracellular referring to whether they are active inside or outside the cell respectively

Intracellular enzymes are produced and function inside the cell

Extracellular enzymes are secreted by cells and catalyse reactions outside cells (eg. digestive enzymes in the gut)