Enzymes are essential for life Flashcards
What are the three types of change in gibbs free energy a biological process can be in?
G less than 0 (negative) you’re releasing energy (high energy to low energy state), spontaneous, does not mean fast - speed refers to the kinetics/rate of the reaction
G more than 0 (positive) you’re using energy (low energy to high energy state), non-spontaneous
G = 0 you’re at equilibrium, can’t do work
What is the metabolic network?
Biochemical synthesis and degradation uses pathways of enzyme-catalysed steps.
Network of all of these reactions 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 negative (proceed in forwards direction)
How do enzymes affect the timescale of life?
Enzymes speed up reactions to the ‘timescale of life’. Reactions pass through high-energy transition states. Activation energy is required to reach transition state and enzymes lower the activation energy of the system allowing the reaction to occur (can reduce activation energy)
How are enzymes catalysts?
Enzymes mainly affect the speed and kinetics of the reaction, accelerate forwards and reverse reactions equally, overall delta G is not changed. Enzymes are almost always proteins (occasionally RNA)
What are some classes of enzymes?
Oxidoreductases : redox i.e. transfer of electrons, enzymes either reducing or oxidising things
Transferases : transfer of a functional group
Hydrolases : hydrolysis reactions using H2O
Lyases : Non hydrolysis breaking or making bonds (not using water)
Isomerases : Transfer of atoms/groups within a molecule to yield an isomeric form
Ligase : Join two molecules together (i.e. for a new bond; usually coupled to ATP cleavage)
What are co-factors?
Cofactors are non-protein factors that can help many enzymes catalyse reactions. They sit at the active site and provide chemical properties that can’t be provided by the native amino acids. Two classes of a cofactor are metal ions and coenzymes
How are metal ions involved with enzymes?
Metal ions are lewis atoms (electron acceptors), so they can participate in acid-base catalysis very effectively. Form coordination compounds with precise geometrics for positioning reactants exactly where they need to be e.g. magnesium ions, zinc ions and iron irons
What are co-enzymes?
Coenzymes are small organic molecules, co-substrates, carriers of electrons, atoms or functional groups and are often derived from vitamins
How does hexokinase allow reaction coupling?
Reactants lower than products so non-spontaneous, delta G is positive 13.8 however if we add hexokinase (which has the ability to hydrolyse ATP) the difference between reactants and products for hydrolysing ATP is -35 hence it is spontaneous so will give out energy so overall G is -16.7 hence the reaction is spontaneous and can proceed
Key points regarding enzymes and catalysis
Enzymes catalyse thermodynamically favourable reactions by lowering the activation energy and can couple non-spontaneous reactions with spontaneous reactions allowing them to proceed
