1.4- Enzymes Flashcards
What are enzymes?
tertiary proteins- where the polypeptide chain is folded back on itself into a spherical globular shape which increase the rate of a metabolic reaction by lowering the activation energy
How are enzymes specific?
each enzyme reacts with a particular substrate molecule
each enzyme will catalyse only one particular reaction
each enzyme has its own 3D globular shape maintained by tertiary protein bonding
What’s an enzyme -substrate complex?
the substrate molecule is complimentary to the active site which fits into and binds to the active site within the enzyme
What’s the lock and key theory?
there is an exact fit between the substrate and the active site of the enzyme
What’s the induced fit theory?
when the enzyme and substrate form a complex, the structure of the enzyme is altered so that the active site of the enzyme fits around the substrate
What’s an example of an induced fit theory?
lysozyme
What are anabolic enzymes?
build larger products from smaller substrate molecules
What are catabolic enzymes?
break large substrate molecules into smaller products
What is activation energy?
the energy needed to break existing chemical bonds inside molecules at the start of the reaction
What does intracellular mean?
catalyse reactions inside of cells e.g ATP Synthase, DNA helicase which unwinds the helix
What does extracellular mean?
catalyse reactions outside of cells e.g digestive enzymes secreted by the cell
What factors affect enzyme activity?
temperature
pH
substrate concentration
enzyme concentration
How does an increase in temperature affect enzyme activity?
it increases the rate of reaction because it gives the molecules greater kinetic energy, the enzyme and substrate molecules move around more quickly, increasing the chance of molecules colliding, this leads to the formation of more successful enzyme-substate complexes, which will continue until the optimum temperature is reached
What is the optimum temperature?
the temperature enzymes work best
where the most successful collisions take place
What happens to then enzyme when the temp is further increased after the optimum temp?
the kinetic energy increases to a point where vibrations in the enzyme molecule weaken some bonds holding the 3D tertiary structure of the active site together. The active site loses its shape, the substrate is no longer complementary to the active site, no further enzyme-substrate complexes can be made, and the enzyme is denatured, decreasing the rate of reaction
What happens to the enzyme activity at low temperatures?
as there’s low kinetic energy, the enzyme and the substrate molecules collide less often, so fewer successful enzyme substrate complexes form, meaning the product is produced slowly
What happens when the substrate concentration is increased?
As enzyme reaction relies on successful collisions between enzymes, an increase in the substrate concentration will increase collisions and the rate of reaction. Therefore, at low substrate concentrations, it is this factor that is limiting the rate of reaction
Any further increase in substrate concentration, has no effect on the rate of reaction. It is no longer the limiting factor. The rate of reaction plateaus as the active sites are occupied, having formed successful enzyme substrate complexes
The enzyme concentration is the limiting factor now
How does pH affect enzyme activity?
Small changes from the optimum pH, either above or below, make small reversible changes in the enzyme molecule reducing its efficiency. Large changes in pH can disrupt ionic and hydrogen bonds in the enzyme causing permanent changes to the shape of the active site. This prevents the formation of enzyme/substrate complexes, denaturing the enzyme
What does limiting factor mean?
a factor is limiting when an increase in its value causes an increase in the rate of reaction
What happens when the enzyme concentration is increased?
the rate of reaction increases as enzyme concentration increases as there are more active sites for substrates to bind to, however increasing the enzyme concentration beyond a certain point has no effect on the rate of reaction as there are more active sites than substrates, so substrate concentration becomes the limiting factor
What is an inhibitor?
is a substance which slows down or stops a reaction by affecting the binding of substrate to the enzymes
What are two types of inhibitors?
reversible and irreversible
What is a reversible inhibitor?
bind to the active site through hydrogen bonds and weak ionic interactions therefore they do not bind permanently
What are the types of reversible inhibitors?
competitive and non-competitive inhibitors
