Enzymes Flashcards
enzymes
they are biological catalysts, remain unchanged so they can be used again and again, can be anabolic or catabolic, all are proteins so are made during protein synthesis, they are globular proteins and have a well developed tertiary structure, can be intracellular or extracellular
anabolic
make larger molecules from smaller molecules
catabolic
break down larger molecules into smaller molecules
what does it mean if an enzyme is intracellular?
enzymes that remain inside the cell and act as catalysts for processes taking place within the cell
what does it mean if an enzyme is extracellular?
enzymes that are secreted out of the cell and used to catalyse reactions taking place in body cavities such as the gut
lock and key hypothesis
idea of substrate fitting exactly into the active site, bonds stabilise the substrate in the active site and form an enzyme-substrate complex, bonds in the substrate are put under strain and is converted to product which is forming an enzyme product complex, products are then released and the enzyme active site is free to catalyse another reaction
induced fit model
suggests that the active site is nearly complementary to the substrate, but moulds around the substrate to fit it more closely, this helps to strain on the bonds in the substrate
activation energy
it is an energy barrier that is needed to be overcome in order for a molecule to react, can often be overcome with high temperatures or pressures
factors affecting enzyme activity
temperature - as temperature increases the kinetic energy increases of both enzyme and substrate molecules, increases chances of successful collisions and the formation of an enzyme substrate complex, if temperature gets too high the enzyme will become denatured, low temperatures do not denature enzymes just reduces rate of reaction
Q10 = rate of reaction at (x + 10)/rate of reaction at x
pH - changes in pH can affect the tertiary structure of enzymes, causing them to denature and preventing the formation of a enzyme-substrate complex
substrate concentration - the higher the substrate concentration, the higher the chances of successful collisions
enzyme concentration - if the enzyme concentration is increased, more active sites are available for the substrate molecules to fit into and more enzyme-substrates can be formed
enzyme inhibition
molecules that bind to enzymes and decrease their rate of reaction or stop it completely, affect the active site so that less enzyme-substrate complexes form or can no longer form
irreversible inhibitors
some inhibitors form covalent bonds with enzymes and inhibit them permanently known as irreversible inhibitors, enzyme is completely inactivated and the cell will need to produce more of the enzyme
reversible inhibitors
other enzymes bind temporarily with enzymes and their affect can be reversed by a change in the environment, two main categories of reversible inhibitors: competitive inhibitors and non-competitive inhibitors
competitive inhibitors
they have a similar shape to the substrate and a complementary shape to the active site and so compete with the substrate to bind to the active site, competitive inhibitors prevent the substrate binding and therefore lower the number of enzyme-substrate complexes that can be formed, if the concentration of substrate in a mixture of enzyme, substrate and competitive inhibitor then the level of inhibition is decreased
non-competitive inhibitors
they attach to another part of the enzyme known as the allosteric site and changes the shape of the active site, any change in substrate concentration will not affect the level of inhibition
metabolic pathways
series of linked, often enzyme controlled reactions that happen in an organism or cell, can be controlled by end product inhibition, if a metabolic pathway becomes too active the final product inhibits one of the enzymes that catalyses an earlier step in the metabolic pathway so less product is formed
