Summary
Summary Enzymes
- Module
- Unit 3 - C Enzymes
- Institution
- CIE
Biology A level revision notes on enzymes
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EnzymesEnzymes are protein molecules, which can be defined as biological
catalysts. A catalyst is a molecule, which speeds up a chemical reaction but
remains unchanged at the end.
Enzymes that work within cells are called intracellular enzymes. Enzymes
that are secreted by cells and catalyse reactions outside cells are described as
extracellular eg. Digestive enzymes in the gut.
Enzymes are globular proteins and are coiled into a 3D shape, with
hydrophilic R groups on the outside of the molecule to ensure that they are
soluble.
When the substrate enters the active site, it is held in place by temporary
bonds, which form between the substrate and some of the R groups of the
enzyme’s amino acids. This forms an enzyme-substrate complex.
The enzyme is always specific for the substrate but the enzyme and substrate
can sometimes change shape slightly as the substrate enters to ensure a
perfect fit.
In a chemical reaction the substrate needs
extra energy in order to react and this energy
required is called activation energy.
In a reaction, when the enzyme and substrate
are first mixed, there are a large number of
substrate molecules, which means all the
enzymes will be in constant use (binding
with a substrate to form an ESC). The rate of
reaction depends on how many enzymes
there are and the speed that the enzyme can
convert the substrate to a product. However as more substrate is converted
into product, there are fewer substrate molecules to bind with an enzyme so
the reaction slows, as enzymes have to wait for substrates. The reaction will
eventually stop when there are no more substrates.
Factors that affect enzyme action
Temperature
Increasing temperature increases the kinetic energy that molecules possess.
In a fluid, this means that there are more random collisions between
molecules per unit time.
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