Enzymes and coenzymes Flashcards
what is an enzyme?
biological catalysts which speed up rate of reaction - without altering the final eqm between reactants and products
they are not used up and are regenerated
are enzymes efficient?
extremely - catalase catalyses break down of H2O2 to water 10^4 times faster than the uncatalyzed reaction at 30C
how do enzymes catalyse reactions?
they provide an alternative pathway for the reaction with a lower activation energy
- binding energy decreases overall energy by stabilising the transition state, orienting the substrates correctly and distorting reactants to a reactive state
- it is reversible reaction
what is an isoenzyme?
enzymes that catalyse the same reaction but are different gene products
what does enzyme specificity mean
enzymes will only catalyse one reaction with specific substrate(s), including differences in stereoisomers
what is specificity determined by?
the shape of the active site where only the correct shaped and charged substrate can fit
what are the consequences of enzyme specificity?
group of enzymes present together in one compartment of a cell e.g. cytoplasm of muscle cells, can give rise to a complex and co-ordinated metabolic pathway
what are the 6 main classes of enzyme?
oxidoreductase transferase lyase hydrolase isomerase ligase
what does oxidoreductase enzyme do?
catalyse transfer of H atoms and electrons (redox reactions)
what does transferase enzyme do?
catalyse transfer of functional groups from donors to acceptors
what does lyase enzyme do?
catalyse cleavage of C-C, C-O, C-N bonds (addition of groups to double bonds or formation of double bonds by removal of groups)
what does hydrolase enzyme do?
catalyse cleavage of bonds by addition of water (hydrolysis)
what does isomerase enzyme do?
catalyse transfer of functional group within the same molecule
what does ligase enzyme do?
use ATP to catalyse formation of new covalent bonds
what are the other three enzymes and what do they do?
phosphorylase - addition of inorganic P group
kinase - addition of P from ATP
phosphatase - removal of P group
what is the structure of an enzyme?
tertiary proteins - folded into complex 3D structures
stabilised by many weak bonds
what bonds stabilise enzymes?
H bonds, ionic bonds, hydrophobic interactions
what are the weak bonds in enzymes affected by?
easily broken
affected by temp and pH
generally sensitive to their environment
what determines the shape of the active site?
amino acid side chains
- they are involved in the formation of ESCs
other parts if aa are used to channel the enzyme to the active site as part of the catalysis process
what are the two models that allow binding of substrate to AS?
lock and key
induced fit
how does lock and key work?
substrate fits directly into active site
how does induced fit work?
conformation of the enzyme
- substrate binds in closed configuration
- active site forms around the substrate
how does temp affect enzymes?
- ROR inc up until the optimum temperature
- rate then dec as weak bonds in tertiary structure are broken so enzyme denatures and loses active site
hoe does pH affect enzymes?
pH affects the weak bonds and so ROR will be fastest at optimum pH
-pH changes cause reversible changes to the enzyme as they will accept/donate a proton depending on the environment
what is a co factor?
any substance that is required for an enzyme to be catalytically active
what are coenzymes?
organic cofactors e.g. NAD
what do co substrates do?
transfer groups from one enzyme to another
what are prosthetic groups and their function?
co factors that are tightly bound to the enzyme and remain attached to it when catalysing the reaction; remain unchanged at the end of the reaction cycle
