Enzymes are Essential for Life Flashcards
What are the major classes of enzymes?
oxidoreductases (redox)
transferases (transfer of a functional group)
hydroliase (hydrolysis reaction using water)
lyases (non-hydrolytic breaking or making of bonds)
isomerases (transfer of groups/atoms within a molecule to yield and isometric form)
ligases (join to molecules together by forming a bond)
what is a cofactor and what purpose do they serve?
non-protein “factors” that help enzymes catalyse reactions
what are the two major classes of cofactor and how do they work?
co-enzymes: small organic molecules that are co-substrates. they carry electrons, atoms or functional groups, and are often derived from vitamins.
metal ions: are lewis acids (ie. proton acceptors), so they can participate in acid-base catalysis. they form compounds with precise geometrics (good for positioning reactants exactly where they need to be)
what is reaction coupling and how do enzymes mediate this?
reaction coupling is when a spontaneous reaction is coupled with a non-spontaneous reaction so that both proceed (the spontaneous reaction has to have a large enough negative delta G that its still negative once coupled to the delta G positive one). enzymes allow reaction coupling.
describe how life is not at equilibrium
delta G smaller than zero will be spontaneous and energy will be released.
delta G larger than zero will be non-spontaneous and energy is required to make it happen.
when delta G is equal to zero then no work can happen.
This shows us that life is not at equilibrium, because we need changes in free energy for chemical or biological reactions to occur, but life can be at a steady state.
describe the difference between kinetics and thermodynamics
It is important to note that spontaneous does NOT mean fast.
- Thermodynamics (energy) determines whether it will be spontaneous or not
- Kinetics (rates) determines how fast the reaction will occur
describe the metabolic network
biochemical synthesis and degradation uses pathways of enzyme catalysed steps
- this network keeps (most) of the individual steps away from equilibrium
enzymes can couple a spontaneous reaction to a non-spontaneous one, to make the overall delta G less than zero
how do enzymes catalyse thermodynamically favourable reactions?
by lowering the activation energy
- by decreasing the change in Gibbs energy of the transition state, enzymes accelerate the forward and reverse reactions equally
- the overall Gibbs energy for the reaction has not changed
- enzymes are almost always proteins (occasionally RNA)
eg. glycogen phosphorylase
The enzyme glycogen phosphorylase takes a free phosphate and adds it onto the end sugar of the glucose molecule. It then splits that one glucose-1-phosphate from the rest of the glycogen. This lowers the activation energy and speeds up the rate of the reaction massively.
what are some common examples of metal ions
- Mg2+: DNA pol, hexokinase, pyruvate kinase
- Zn2+: Alcohol dehydrogenase, carbonic anhydrase
- Fe2+ or Fe3+: Cytochrome oxidase, peroxidase
