Enzymes Flashcards
What are enzymes and how do they work?
Enzymes are biomolecules (mostly proteins) that contain an active site comprised of amino acids with reactive groups (e.g. Asp, Lys, Cys, His & Ser) that catalyse the conversion of the substrate (S) to product (P) usually with exquisite specificity. They work by using different catalytic mechanisms (eg. weak interactions, acid-base, covalent & metal ion catalysis) that lower the activation energy of the reaction and thus enhance the reaction rate, but do not affect the reaction equilibrium.
What are enzymes in biology?
Metabolism: in vivo processing of carbon food sources into energy (ATP) and the synthesis of important biomolecules (e.g. DNA, glycogen, lipids, proteins, RNA) that are essential for supporting life.
What are enzymes in medicine?
Many drugs target essential enzymes (e.g. RELENZA or zanamivir inhibits neuriminidase from influenza virus) - Clinical enzymology for diagnosis & prognosis of medical conditions, such as a myocardial infarction (which results in the release of enzymes from cardiac muscle cells, such as CK, AST & LDH)
What are enzymes in the industry?
Involved in the manufacturing of foods (e.g. chymosin used in cheese production), as well as detergents, soaps, chemicals, etc.
Define the active site
These are areas on the enzyme that are lined with amino acid residues with substituents that bind the substrate and catalyse its transformation. Normally found in a cleft or cleave (hole) in the enzyme.
Define activation energy
The energy barrier (ΔGǂuncat) required for the substrate to transform into the desired product. Enzymes lower the activation energies through stabilising the transition states.
Define transition state
This is the unstable formation of a substrate that is required to transition the substrate to the product, the configuration associated with the activation energy.
Define initial state
This is the initial enzymatic linear rate when substrates are introduced to the enzymes. Generally, the higher the [S], the faster this initial rate
Define steady-state kinetics
The period of time in which the concentration of the enzyme-substrate (ES) intermediate is constant, whilst S is decreasing in concentration and P increasing in concentration
Define Km
½ Vmax, which is equal to the [S] at ½ Vmax also.
Define Vmax
This is the maximum velocity achieved at increasing [S], it is an asymptote which is controlled by the enzyme concentration because at this point the enzymes are saturated by substrate.
How do you experimentally determine Km and Vmax for an enzyme?
First you have to experimentally determine the initial velocity (V0) of differing substrate concentrations by plotting [S] against time. This then allows you to plot V0 against [S], which will allow you to find the Vmax asymptote. ½ Vmax equals Km, which also equals [S].
You can also plot the inverse, creating Lineweaver-burk plot. Where the lone crosses the y-axis = 1/Vmax, and where it crosses the x-axis = -1/km.
