Enzymes

• Heat is often used in labratories to speed up chemical reactions, but this can damage cells.
• Chemical reactions inside cells are called metabolism.
• Enzymes are biological catalysts which are globular proteins.
• Anabolic reactions build bigger molecules, enzymes reduce the compulsion between them.
• Catabolic reactions break apart large molecules, by putting strain on the molecules so they come apart easier.
• Intracellular enzymes are inside the cell, such as catalase which breaks down hydrogen peroxide, a toxic by-product of cellular reactions, into oxygen and water.
• Extracellular enzymes are outside the cell such as pepsin, trypsin, amylase and maltase. Amylase is found in the saliva and causes hydrolysis of starch into maltose in the mouth.
• Enzymes can have a primary, secondary or tertiary structure.
• In the induced fit model, the active site is slightly altered to fit the substrate.
• The interactions formed when a substrate enters the active site can either be anabolic or catabolic.
• The lock and key model is a model of enzyme-substrate interactions in which the active site is complementary to the substrate.
• Increased temperature increases the kinetic energy of molecules, so successful collisions are more likely. After optimum temp, the rate of reaction decreases as the enzymes begin to vibrate too much which causes bonds to break, which change the shape of the enzyme. They can't fit the substrate.
• When above/below optimum pH, OH- and H+ ions break the ionic and hydrogen bonds holding the tertiary shape together. This changes the active site shape so it's can't fit the substrate. Most humans enzymes work at pH7 whilst pepsin works at pH2 as it found in the stomach.
• As enzyme conc. increases so does rate of reaction until substrate conc. becomes a limiting factor if no more are added. The rate will eventually plateau at Vmax when enzymes are available for each substrate.
• As substrate concentration increase, so does rate of reaction. This reaches saturation point when all active sites are used up, so the enzyme conc. becomes the limiting factor. Rate of reaction can decrease over time as more substrate turns into products.
• Cofactors are non-proteins compounds required for enzyme activity to occur.
• Prosthetic groups permanently bind to enzymes, now called conjugated proteins. They contribute to charges on the enzyme surface, altering the tertiary shape so that the enzyme is complimentary. An example is the iron group on haemoglobin.
• Inorganic factors are inorganic ions/molecules. They help the substrate bind to an enzyme.
• Organic cofactors (coenzymes) participate in reactions and act like substrate and are changed.
• Inhibitors prevent substrate from binding to enzymes permanently or temporarily.
• Competitive inhibitors bind to the active site temporarily, and take up the place of a substrate not allowing it to bind.
• Non-competitive inhibitors bind to the allosteric site, and change the shape of the enzyme, so substrate can't bind.
• Competitive slow rate of reaction, but they will still reach the original Vmax, whilst non-competitive prevent the rate of reaction from increasing, causing it to reach Vmax sooner, as substrate can't bind to non-complimentary enzymes.
• Reversible inhibition usually uses competitive inhibitors. They bond due to the weak hydrogen/ionic bonds.
• Irreversible inhibition is when an irreversible inhibitor covalently bonds with the enzyme, changing its structure forever. This means that the enzyme cannot be used again.
• Omeprazole reduces production of H+ ions, reducing production to acid in the stomach.
• Penicillin is a competitive inhibitor that weakens bacterial cell walls by catalysing the making of proteins in walls so that the cells can't control their osmotic pressure and burst.
• Antiviral drugs inhibit the enzyme reverse transcriptase which catalyses the replication of viral DNA.
• Cyanide is a non-competitive inhibitor, which reduces ATP production by binding to cytochrome oxidose. Malonate is competitive and binds to succinate dehydrogenase, arsenic is non-competitive and binds to pyruvate dehydrogenase. All these enzymes catalyse ATP production.
• Ethylene glycol breaks down into oxalic acid which is toxic to the body. Ethanol is a similar shape to the substrate so can act as a competitive inhibitor and prevent glycol from breaking down.
• End product inhibition is when the product of a reaction is the same as the substrate, so an increased concentration of the product will inhibit an enzyme in an earlier stage. An example of this phosphofructokinase, involved in breaking down glucose in ATP, so high levels of ATP prevent anymore being made.