What are enzymes? All enzymes are globular proteins → spherical in shape (Fig 1) Control biochemical reactions in cells They have the suffix "-ase" Intracellular enzymes are found inside the cell Extracellular enzymes act outside the cell (e.g. digestive enzymes) Enzymes are catalysts → speed up chemical reactions (Fig 2, Fig 3) Reduce activation energy required to start a reaction between molecules Substrates (reactants) are converted into products Reaction may not take place in absence of enzymes (each enzyme has a specific catalytic action) Enzymes catalyse a reaction at max. rate at an optimum state Lock and key theory Only one substrate (key) can fit into the enzyme's active site (lock) Both structures have a unique shape Induced fit theory (Fig 4) Substrate binds to the enzyme's active site The shape of the active site changes and moves the substrate closer to the enzyme Amino acids are moulded into a precise form Enzyme wraps around substrate to distort it This lowers the activation energy An enzyme-substrate complex forms → fast reaction E + S → ES → P + E Enzyme is not used up in the reaction (unlike substrates) Fig4 Fig1 Enzyme Activity Changes in pH Affect attraction between substrate and enzyme Ionic bonds can break and change shape → enzyme is denatured Charges on amino acids can change → ES complex cannot form Optimum pH (enzymes work best) pH 7 for intracellular enzymes Acidic range (pH 1-6) in the stomach for digestive enzymes (pepsin) Alkaline range (pH 8-14) in oral cavities (amylase) pH measures the conc. of hydrogen ions → higher conc. will give a lower pH Enzyme conc Proportional to rate of reaction, provided other conditions are constant Straight line Substrate conc. (Fig 5) Proportional to rate of reaction until there are more substrates than enzymes present Rate of reaction increases Substrate binds to active site, but more enzymes are available Rate increases if more substrate is added Eventually, curve becomes constant (no increased rate) Substrates occupy all active sites (all enzymes) Adding more substrate won't yield more product, as no more active sites are available Increased Temperature Increases speed of molecular movement → chances of molecular collisions → more ES complexes At 0-42°C rate of reaction is proportional to temp Enzymes have optimum temp. for their action (usually 37°C in humans) Above ≈42°C, enzyme is denatured due to heavy vibration that breaks -H bonds Shape is changed → active site can't be used anymore Decreased Temperature Enzymes become less and less active, due to reductions in speed of molecular movement Below freezing point Inactivated, not denatured Regain their function when returning to normal temperature Thermophilic: heat-loving Hyperthermophilic: organisms are not able to grow below +70°C Psychrophiles: cold-loving Enzymes - Heroes and Villains Analytical reagents Made up of 2 enzymes (glucose oxidase and peroxidise) and a colourless hydrogen-donor fixed on a strip The strip is dipped into a test solution (urine) Colour develops which indicates that glucose is present This method is used by diabetics to monitor their blood glucose levels In healthy people, the urine contains NO glucose Glucose oxidase Highly sensitive to low conc. of glucose Highly specific because it only reacts with one specific substrate (glucose) Catalyses the conversion of glucose to hydrogen peroxide (H2O2) Peroxidase Catalyzes reaction between colourless hydrogen-donor molecule and H2O2 A coloured molecule is formed Alpha1-antitrypsin Function White blood cells (neutrophils) in the lung help to prevent infections They also release elastase and protease (trypsin) Those enzymes break down/digest ct. and proteins inside the lungs and damage it NB: Trypsin is also found in the digestive system and digests food! The anti-protease alpha1-antitrypsin protects the lungs from elastase and protease Alpha1-antitrypsin deficiency Genetic disease that causes emphysema Trypsin is no longer inhibited and damages the lungs Walls of alveoli are damaged and surface area for gas exchange is reduced Patients can be treated by infusing alpha1-antitrypsin Smoking Increases the number of neutrophils in the lungs (more trypsin is secreted into the lungs) ALSO inactivates alpha1-antitrypsin This creates an imbalance between proteases (trypsin) and anti-proteases (α1-antitrypsin) Same lung damage as in α1-antitrypsin deficiency but much slower Lactose intolerance Lactase splits lactose (milk sugar) into β-glucose and galactose Lactose intolerant person lacks lactase → lactose is neither digested nor absorbed High levels of soluble lactose remain in small intestine Supports large populations of bacteria / ferment lactose producing gas / causing abdominal discomfort Water potential becomes more negative / H2O moves into small intestine / not reabsorbed / diarrhoea Adults rarely produce lactase / gene is switched off in adulthood Pancreatitis Pancreas is found below the stomach Produces digestive enzymes (amylase, lipase, trypsin that break down starch, lipids, proteins, respectively) Acute (sudden onset) Reversible inflammation of a previously normal pancreas Caused by gallstones, alcohol, scorpion bite, trauma Inappropriate activation of enzymes Trypsin becomes active before released from the pancreas Pancreas is made of proteins Trypsin is active and digests/hydrolyses proteins Cell wall breaks down, amylase and lipase escape into the blood Diagnosis Amylase and lipase remain elevated in blood for 3 days Chronic (gradual onset) Inflammation is caused by cystic fibrosis or long-term alcohol intake Pancreas gradually loses its ability to produce digestive enzymes Food is not digested, hence not absorbed (malabsorption) Diagnosis Amylase and lipase in blood normal Low levels of faecal elastase Too much fat in faeces → fat passes through gut without being digested and absorbed Pancreatic enzyme replacement therapy (PERT) Required for life in patients with irreversible pancreatic damage Chronic pancreatitis Cystic fibrosis Tablet contains digestive enzymes (normally produced by pancreas) Degradation of enzymes/proteins by stomach acid prevented by Coating tablet with protective layer Taking extra tablet that inhibits acid secretion