Chapter 4 Enzymes Flashcards
Why are enzymes important
Enzymes are biological catalysts and interact with substrate molecules causing them to react at faster rates.
The role of enzymes in reactions
Living organism need to built and maintained, which involves synthesis of large polymers.
Enzymes are required for anabolic (building up) reactions and catabolic (breaking down) reactions.
Activation energy
The energy required for the reaction to start. Enzymes decrease the activation energy allowing reactions to occur more efficiently.
Lock and Key hypothesis
Enzymes have an active site which can only have one substrate fitting into it. The same way that only the right key will fit into a lock, only a specific substrate will fit the active site of an enzyme. When a substrate is bound to the active site it is called the enzyme substrate complex. Once reacted they are called the enzyme product complex.
The R- groups in the enzyme interact with the substrate creating temporary bonds.
Induced fit hypothesis
Enzymes active sites actually change shape slightly as the substrate enters - called induced fit hypothesis.
The initial interaction between enzymes and substrates is weak but this induces changes in the enzymes tertiary structure that strengthen binding, putting strain on the molecule. The weakens bonds, hence lowering activation energy.
Intracellular enzymes
Work within the cells that produce them
They have anabolic and catabolic pathways
anabolic - build complex molecules from simpler ones
catabolic - break down complex molecules to simpler ones.
E.g. catalase breaks down hydrogen peroxide ( toxic) into oxygen and water in the plant and animal tissues
Extracellular enzymes
Extracellular enzymes act outside the cells that produce and secrete them.
E.g.
Amylase - This is secreted by the salivary glands, pancreas, and small intestine to break down starch into maltose.
Trypsin - This is secreted by the pancreas into the small intestine to break down proteins into smaller polypeptides.
Temperature
As temperature increases, the rate of reaction increases. The molecules have more kinetic energy, causing more collisions and enzyme-substrate complexes
The maximum rate is reached at the optimum temperature. The optimum temperature is the temperature this enzyme works fastest at.
As temperature increases past the optimum, the rate of reaction decreases until the reaction stops. Too much kinetic energy causes the active site to change shape and the enzyme denatures.
Temperature coefficient
The temperature coefficient (Q10) is a value that shows how much the rate of reaction changes when the temperature is increased by 10°C.
Temperature 10°C = RoR at 10°C higher/ RoR at original.
pH
Below the optimum pH, the rate of reaction is low or zero. In acidic conditions, H+ ions break ionic/hydrogen bonds and denature enzymes.
The maximum rate of reaction is reached at the optimum pH. The optimum pH is the pH the enzyme works fastest at.
Above the optimum pH, the rate of reaction is low or zero. In alkaline conditions, OH- ions break ionic bonds or hydrogen bonds and denature enzymes.
Substrate concentration
As the substrate concentration increases, the rate of reaction increases. There are more substrate molecules to form more enzyme-substrate complexes.
As the substrate concentration increases further, the rate of reaction plateaus (levels off).This is the saturation point, which is when all active sites are occupied by a substrate and enzyme concentration becomes the limiting factor.
Enzyme concentration
As the enzyme concentration increases, the rate of reaction increases. There are more enzyme molecules to form more enzyme-substrate complexes.
As the enzyme concentration increases further, the rate of reaction plateaus (levels off). All substrate molecules available are being acted upon and substrate concentration becomes the limiting factor.
What are inhibitors
they are molecules that prevent enzymes from carrying out their normal function of catalysis. There are two types of enzyme inhibition - competitive and non-competitive.
How does competitive inhibition occur?
a molecule or part of a molecule that has a similar shape to the substrate of an enzyme can fit into the active site of the enzyme.
this blocks the substrate from entering the active site, preventing the enzyme from catalysing the reaction.
the enzyme can’t carry out its function so it is inhibited.
the non-substrate molecule that binds to the active site is a type of inhibitor, it will compete with the substrate to go to the active site and for this reason it slows down the rate of reaction. For this reason they are called competitive inhibitors.
Effects on rates of reaction - competitive
it reduces the rate of reaction for a given concentration of a substrate but it doesn’t change the Vmax of the enzyme it inhibits. If the substrate concentration is increased then there will be so much of the substrate that they will out compete the inhibitors and the original Vmax can be reached.
