enzymes Flashcards
(16 cards)
what are the four categories of amino acid residues
- catalytic amino acid residues (making or breaking of chemical bonds)
- binding amino acid residues (hold the substrate(s) in
position via non-covalent bonds) - structural amino acid residues (maintaining the specific 3D
conformation of the active site) - non-essential amino acid residues (no specific function)
what are the three main types of cofactors
- inorganic metal ions (bind reversible to enzymes and alter the active/allosteric site to facilitate catalysis)
- coenzymes (transient carriers of specific functional groups, hydrogen or electrons)
- prosthetic group (permanently, tightly bound to enzyme)
how do enzymes lower activation energy
- orientating substrates in close proximity and in correct orientation
- straining critical bonds in substrate to attain unstable transition state
- providing a micro environment that favours the reaction
describe the lock and key hypothesis
there is an exact fit/complementary shape/conformation between substrate and enzyme’s active site , just like how a key fits into a lock very precisely — the enzyme is viewed as a rigid structure
describe the induced fit hypothesis
in addition to substrate specificity in ‘lock and key’ hypothesis, this further explains group specificity. the enzyme has an active site that is flexible rather than rigid in conformation, allowing more than one type of substrate to bind (not in precise complementary conformation before binding). upon binding, the active site changes its conformation slightly the substrate fits even more firmly/snugly so that the R groups of the catalytic amino acids at the active site are:
moulded into a specific conformation
brought into close proximity to the chemical bonds in the substrate hence facilitating catalysis
how does substrate concentration affect rate of enzymatic reaction
at low conc: proportional/steep/rapid increase. not all active sites are occupied, rate is limited by substrate conc., increase in frequency of effective collisions, increase in e-s complex formed + amount of product formed per unit time
at high conc: increase is more gradual, graph eventually reaches a plateau. active sites are saturated, added substrates must wait for existing e-s complexes to dissociate to release products then form new e-s complexes; enzyme conc is limiting instead of substrate conc
how does enzyme concentration affect rate of enzymatic reaction
at low conc: proportional/steep/rapid increase. provides more active sites. increases frequency of effective collisions, more e-s complexes and product formed per unit time.
at high conc: gradual increase, graph reaches a plateau. not enough substrate molecules competing for active sites, substrate conc is limiting instead of enzyme conc.
how does temperature affect rate of enzymatic reaction
below optimum temp: rate increases as temp increases. enzymes are inactivated at low temperatures, increase in temp increases KE, thus increasing frequency of effective collisions etc…
beyond optimum temp: decrease in rate despite increasing frequency of collisions. thermal agitation disrupts non-covalent interactions that stabilise the specific 3D conformation of the protein — loss in 3D conformation/denaturation, active site is no longer complementary fit with tithe substrate. frequency of effective collisions decreases etc etc
how does pH affect rate of enzymatic reaction
alters the ionic charge of acidic and basic R groups, disrupts ionic/hydrogen bonds maintaining the 3D conformation of enzyme — denaturation.
At pH values only slightly above and below the optimum pH, many enzymes will
have a marked decline in enzyme activity as the 3D conformation is altered and
affinity for the substrate is correspondingly decreased.
structural amino acid residues: conformation of the active site is no longer complementary to the substrate; binding amino acid residues: substrate cannot be held in correct orientation; catalytic amino acid residues: no longer possess correct ionisation charge to catalyse reaction
what are competitive inhibitors
Competitive inhibitors are structurally similar
to the substrate molecule and compete with
the substrate for binding to the active site. Although it is not acted upon by the enzyme, it remains bound to the active site and prevents substrate binding to active site.
describe and explain how competitive inhibitors affect rate of enzymatic reaction
initial rate of reaction is reduced. when [S] is very high, both reactions reach the same Vmax, but requires a longer period of time to
produce the same amount of product.
increase in [S] reduces effect of inhibition. substrate and the inhibitor are in direct competition for the enzymes’
active sites and the greater the proportion of the substrate molecules, the greater the
chance a substrate can out-compete the inhibitor to enter the active site
what are non-competitive inhibitors
Non-competitive inhibitors bear no structural resemblance to the substrate. It does not compete with the substrate for the active site; it binds to a part of the enzyme molecule that is not the active site altering the 3D conformation of the
enzyme molecule and active site
describe and explain effect of non-competitive inhibitors on rate of enzymatic reaction
initial rate of reaction is reduced. Even when [S] is very high, the initial rate of reaction in the presence of inhibitor does not reach the same Vmax as the reaction that is uninhibited. substrate molecules are unable to bind, certain proportion of enzymes are rendered inactive. As the substrate and the inhibitor are not in direct competition for the same site, an
increase in substrate concentration has no effect on the inhibition. The final amount of product formed is the same as the substrate continues to be converted by any enzymes molecules that are unaffected by the inhibitor.
what is allosteric regulation
regulation of an enzyme by the binding of molecules at an
allosteric site. allosteric activation: stabilised active form of enzymes and increases affinity; allosteric inhibition: stabilise inactive form of enzyme and decreases affinity
what is cooperativity
binding of one
substrate molecule to an active site of a multimeric enzyme triggers the same favourable conformation change in the active sites of all other subunits of the enzyme
advantages of metabolic pathways catalysed by enzymes
- no accumulation of products — products are substrates of subsequent reactions
- reactions modified in a series of small steps, energy can be released in controlled amounts
- each step is catalysed by a specific enzyme, each enzyme cats a point of control, finely balanced portioning of cell metabolites among different pathways.
- products of one reaction is located to become substrate of next enzyme — build up of high local concentrations and reactions can proceed rapidly
- multi-enzyme complex — orders the sequence of reactions and increases efficiency
