Describe the components of an enzyme.
Catalytic residues - catalyses chemical reaction
Contact residues - ensures specific conformation of active site(complementary to substrate)
Structural residues - maintain overall globular shape of molecule
Catalytic, contact residues make up active site - amino acids in 1o are brought together by folding of chain in 2o, predominantly 3o structures
How do enzymes reduce activation energy of a reaction?
1. holding substrates closer together at correct angle, orientation at active site -> successful interaction & collision (anabolic)
2. strain bonds in substrates until they break(catabolic)
Describe the Lock-and-Key hypothesis.
substrate is the "key" with shape complementary to enzyme's active site, enzyme is the "lock", enzyme's active site is the "keyhole".
when enzyme-substrate complex is formed, chances of successful reaction increase.
once products form, no longer fit into the active site & are released into medium; active site free to receive new substrate molecules.
Describe the Induced-fit hypothesis.
initial shape of active site may not exactly be complementary to that of substrate
however, as substrate enters & binds to active site, it induces a conformational change of change in shape of active site -> substrate can fit even more snugly into active site -> allows better interaction between substrate and catalytic residues @ active site for successful reaction.
How is active site complementary to substrate?
1. 3D conformation of active site is complementary to that of substrate, allows greater interaction b/w CG of substrate & catalytic residues of active site -> spatial fit
2. active site chemically compatible to substrate, capable of bonding with each other; substrate of enzyme depends on nature of amino acids making up active site -> chemical fit
What are 4 factors affecting rate of enzyme reaction?
1. pH
2. temperature
3. enzyme concentration
4. substrate
when investigating a given factor(iv), all other factors kept constant & optimum levels
Explain the effect of temperature on rate of enzyme activity.
@ low temps near/below 0oC, enzyme activity low. enzyme inactivated, minimal KE for collision w/ substrate to form E-S complexes
as temp. increase before optimum temp, rate of reaction increases. increase in heat increases KE of substrate & enzyme, increases molecular motion. freq. of successful collisions b/w substrate, enzyme increases; rate of formation of E-S complexes increases -> rate of formation of products increase
@ optimum temp, max rate of reaction. highest frequency of successful collisions b/w substrate & enzyme.
as temp. increases beyond optimum temp, rate of reaction decreases. heat disrupts H bonds, hydrophobic interactions in 2o, 3o structures -> specific 3D conformation of AS lost -> enzyme denatured. substrate can no longer bind to AS of enzyme to form E-S complexes, decreasing rate of formation of E-S complexes -> rate of formation of products decreases.
Explain effect of pH on rate of enzyme activity.
@ optimum pH, max rate of reaction. bonds maintaining 2o, 3o of enzymes intact -> highest frequency of successful collisions b/w substrate & enzyme -> increases rate of formation of E-S complexes -> rate of formation of pdt. increases.
@ pH other than optimum, rate of reaction decreases. change in pH alters ionic charge of -NH3+ and -COO- R groups -> ionic, H bonds maintaining conf. of AS disrupted; loss of specific 3D conf of enzyme & AS(denatured) -> substrate cant bind to AS, rate of formation of E-S decreases, rate of formation of pdt decreases.
Explain effect of enzyme concentration on rate of enzyme activity.
@ low conc, rate low. as conc increases, more AS available for successful collisions w/ substrates -> increase in frequency of successful collisions b/w substrate, enzyme -> rate of formation of E-S complexes increase, rate of formation of pdt increases(still LiFa)
@ very high conc, rate remains constant. increase in conc wont result in further increase in rate, no longer LiFa, substrate conc is LiFa
Explain effect of substrate concentration on rate of enzyme activity.
@ low conc, rate increases w/ increase in conc. many enzyme molecules have unoccupied AS(LiFa)
as conc increases, rate increases linearly. more substrates available for successful collisions b/w substrate, enzyme -> increase in frequency of successful collisions b/w enzyme, substrate -> rate of formation of pdt increases(still LiFa)
@ very high conc, as conc increases rate constant. all available AS saturated w/ substrates. enzyme conc now LiFa
How does competitive inhibitor work?
compound w/ similar 3D conformation to substrate, can enter & bind to AS.
when bound to AS, prevents substrate from entering AS, prevents formation of E-S complexes & pdt as E-I complexes formed instead -> decreases rate of reaction.
Explain effect of competitive inhibitor on rate of enzyme activity.
@ low substrate conc, conc of substrate=conc of CI -> frequency of E-S collisions = frequency of E-I collisions. no. of E-S complexes = no. of E-I complexes, low rate.
@ high substrate conc, substrate outcompete CI for binding to AS, frequency of E-S collisions higher than frequency of E-I collisions -> more ES complexes than EI formed, higher rate.
@ very high substrate conc, substrates outcompete CI for binding to AS, allows max rate.
CI reversible, overcome by high substrate conc
How does non-competitive inhibitor work?
compound w/ no structural similarity to substrate, binds to enzyme @ allosteric site, results in conformational change of enzyme, AS altered, substrate cant bind to AS.
formation of EI complexes prevents formation of ES complexes, prevents formation of pdt & rate decreases. effect not changed by substrate conc
can be reversible/irreversible