Enzymes Flashcards
(19 cards)
Enzyme
-A biological catalyst that speeds up metabolic reactions without being used up.
-Does this by lowering the activation energy required for two substrate molecules to join.
-Eg in the formation of collagen, cartilage, blood vessel walls and connective tissue.
Turnover
-Number of reactions an enzyme can catalyse per second.
Active site
-Where substrate molecules bind to the enzyme.
-Each substrate only has one active site.
-Defined by the tertiary structure, only 6-10 amino acids.
-Some enzymes have more than one active site.
Catabolic pathways
-Break down into smaller molecules and release energy.
Anabolic pathways
-Synthesise large molecules from smaller ones using energy.
Intracellular reactions
-Made and kept inside the cell.
-Over 1000 different reactions.
-Reactants and products in these reaction are known as metabolites.
Catalase
-Found in all organisms exposed to oxygen.
-Breakdown of hydrogen peroxide into water and oxygen.
-Turnover of 6 million per second.
-2H2O2 -> O2 + 2H2O
Extracellular reactions
-Made in the cell but work outside of them.
-During digestion enzymes are secreted into the gut lumen to digest food.
-Amylase is produced in the salivary gland and breaks down polysaccharide starch into maltose.
-Trypsin is produced in the pancreas and acts in the small intestine to break down proteins into smaller peptides.
Lock and key model
-Old model for enzyme bonding.
-Shows a specific shaped enzyme on a complementary active site.
Induced fit model
-Newer model.
-Active site changes shape to fit the substrate.
-Moves back after reaction.
Effect of temperature on enzyme activity
-Higher kinetic energy, so more successful reactions and quicker formation.
-Highest at the optimum temperature.
-Afterwards the energy of temperature breaks bonds in enzymes, causing them to break and the enzyme to denature irreversibly.
-Active site can no longer bind with substrate.
Temperature coefficient
-Q10 = rate at higher temp/rate and a lower temperature.
-Shows how much rate of reaction changes every 10C raised of temperature.
-Value of 2 means in doubles, while of 3 means it triples.
Effect of pH on enzyme activity
-Enzymes have optimum pH’s at which the work best.
-Too high or low a pH will lead to H+ and OH- ions binding to the tertiary structure and active site, upsetting it.
-After a certain point the enzyme with denature.
pH buffer
-Something that resists a change in pH to keep it constant.
Effect of substrate concentration on enzyme activity
-Few substrates mean many active sites are free and there is a low rate of reaction.
-An increase meaning more active sites engage.
-Once all active sites are in use no further substrates can bind. The enzyme concentration is now the limiting factor.
Competitive inhibitors
-Have a similar shape to the substrates, bind to active site and block it.
-Means the substrate molecule cannot enter and no reaction is catalysed.
-Affected by concentrations of inhibitors compared to substrates.
Inactivators
-A competitive inhibitor that is non-reversible.
-Most competitive inhibitors are not also inactivators.
Non-competitive inhibitors
-Bind to a site other than the active site (allosteric)
-Disrupt tertiary structure, means active site changes shape.
-Therefore substrates can no longer bind.
-Most of the reactions are irreversible as the shape of the enzyme is altered.
Reversible/non reversible bonds
-Reversible: weaker hydrogen or ionic. Inhibitor can be removed.
-Non reversible: strong covalent bonds. Cannot be removed easily.
