C 1.1 - ENZYMES AND METABOLISM

• what is a catalyst


  a substance that increases the rate of a chemical reaction but is not changed by the reaction (does not use itself)
• what is a benefit of catalysts not being used up

  can catalyse reactions many times thus allowing only small quantities needed to be used in relation to the reactants
• what is an example of a catalyst

  platinum which is an inorganic catalyst
• where/what is platinum used for

  used in the catalytic converters fitted to vehicles with combustion engines, to help convert unburned hydrocarbons in exhaust gas to CO2 and water
• What are enzymes?

  proteins which are biological catalysts
• how are enzymes made

  made via protein synthesis to speed up biochemical reactions
• general equation for an enzyme-catalysed reaction

  substrates -- enzyme --> products
• what would happen if cells did not make enzymes

  chemical reactions would happen slowly
• what is metabolism

  sum of all the interdependent and interacting chemical reactions that occurs in living organisms
• give an example of extracellular reactions happening


  digestion of food inside the intestine
• relationship between metabolic reactions and enzymes

  almost all metabolic reactions are catalysed by enzymes
• are enzymes specific?

  Enzymes are specific to one reaction or a group of reactions
• what is the difference between enzymes and non-biological catalysts

  enzymes are specific but non-biological catalysts can catalyse any reaction
• what must happen due to enzyme specificity

  the body must make large amounts/numbers of different enzymes
• benefits of enzyme specificity

  allows organisms to control metabolism, can control rate of reactions and there are mechanisms to stop enzymes working temporarily
• what are two parts of metabolism

  anabolism and catabolism
• what are anabolic reactions

  build up smaller molecules into larger ones - require energy
• example of anabolism

  photosynthesis (uses energy from light)
• examples of anabolic reactions


  protein synthesis, DNA synthesis, synthesis of complex carbohydrates including starch, cellulose and glycogen
• which anabolic reactions are condensation reactions


  making of macromolecules from monomers using energy form ATP
• What are catabolic reactions?

  break down larger molecules into smaller ones, releasing energy
• in some cases how is energy captured

  by coupling the catabolic reaction to the synthesis of ATP, which can then be used in the cell
• what is an example of catabolic reactions


  digestion of food, cell respiration, digestion of complex carbon compounds
• what kind of proteins are enzymes

  they are globular proteins, with precise three-dimensional structure and chemical properties allowing them to function as catalysts
• what must happen for something to be catalysed


  the substrate/s must bind to the active site
• What is an active site?

  the region on the enzyme where the substrate binds
• what happens when a substrate has bound to the active site

  the shape and chemical properties of the active site and substrate match each other allowing binding
• what happens after the substrate has bound to the active site

  converted into products which will then be released allowing more products to be catalysed
• what is a substrate

  the substance on which an enzyme acts
• how do active sites vary

  depending on the size of substrate
• What forms the active site of an enzyme?

  amino acids which are brought together by the folding of the polypeptides
• state the 4 interactions between substrate and active site to allow induces fit binding

  substrate approach vacant active site, substrate bind, second substrate bind, substrate converted into product
• define induced fit

  enzyme changes shape when it binds the substrate, which alters the shape of the active site
• substrate approaching active site

  until substrate is near enzyme, their direction of movement is random; when it is close enough to interact, chemical properties of the enzyme surface attract the substrate molecule towards the active site
• first substrate binding

  when the first substrate is binding the bond angles and lengths are altered which change the 3D molecular shape of the substrate and active site - induced fit binding
• if there is a second substrate binding

  binds to another part of the active site causing the active site to alter again allowing binding
• substrates converted to product

  products are then released allowing enzyme to become vacant again and return to original state - allow further binding
• what do changes to substrate molecule allow

  make it easier for bonds within them to break and form, converting substrates into products
• when can a substrate bind to the active site of an enzyme


  when it moves very close to it - result of molecular motion
• what is molecular motion

  the movement of particles or molecules in a certain direction