Enzymes - Blue Valley temperature for two enzymes Optimal pH for pepsin (stomach enzyme) ... of an activator stabilizes the active form of the enzyme. ... Enzyme 3 Enzyme 4
Post on 31-Mar-2018
A catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction.An enzyme is a catalytic protein.Hydrolysis of sucrose by the enzyme sucrase is an Hydrolysis of sucrose by the enzyme sucrase is an example of an enzyme-catalyzed reaction
Every chemical reaction between molecules involves bond breaking and bond forming.The initial energy needed to start a chemical reaction is called the free energy of activation, or activation energy (EA).gy ( A)Activation energy is often supplied in the form of heat from the surroundings.
G < O
Progress of the reaction
Enzymes catalyze reactions by lowering the EAbarrier.Enzymes do not affect the change in free-energy (G); instead, they hasten reactions that would occur eventually.y
Animation: How Enzymes WorkAnimation: How Enzymes Work
EA withenzymeis lower
G is unaffectedby enzyme
Progress of the reaction
e Course ofreactionwith enzyme
The reactant that an enzyme acts on is called the enzymes substrate.The enzyme binds to its substrate, forming an enzyme-substrate complex.The active site is the region on the enzyme g ywhere the substrate binds.Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction.
In an enzymatic reaction, the substrate binds to the active site.The active site can lower an EA barrier by Orienting substrates correctly.
b b d Straining substrate bonds. Providing a favorable microenvironment. Covalently bonding to the substrate.
Substrates enter active site; enzymechanges shape so its active siteembraces the substrates (induced fit).
Substrates held inactive site by weakinteractions, such ashydrogen bonds andionic bonds.
Active site (and R groups ofits amino acids) can lower EAand speed up a reaction by acting as a template forsubstrate orientation,
stressing the substratesand stabilizing thetransition state,
providing a favorablemicroenvironment,Active
participating directly in thecatalytic reaction.
Substrates areconverted intoproducts.
for two newsubstrate
Each enzyme has an optimal temperature and pH in which it can f ti
Optimal temperature fortypical human enzyme
Optimal temperature forenzyme of thermophilic
0 20 40 60 80 100function.An enzymes activity can also be affected by chemicals that specifically influence the enzyme.
Temperature (C)Optimal temperature for two enzymes
0 20 40 60 80 100
Optimal pH for pepsin(stomach enzyme)
Optimal pHfor trypsin(intestinalenzyme)
pHOptimal pH for two enzymes
0 1 2 3 4 5 6 7 8 9 10
Cofactors are nonprotein enzyme helpers.Coenzymes are organic cofactors.
Competitive inhibitors bind to the active site of an enzyme, competing with the substrate.N titi
A substrate canbind normally to the
active site of anenzyme.
A competitiveinhibitor mimics the
substrate, competingfor the active site.
Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective.
Noncompetitive inhibitorNoncompetitive inhibition
A noncompetitiveinhibitor binds to the
enzyme away from theactive site, altering the
conformation of theenzyme so that its
active site no longerfunctions.
Chemical chaos would result if a cells metabolic pathways were not tightly regulated.To regulate metabolic pathways, the cell switches on or off the genes that encode specific enzymes.enzymes.
Allosteric regulation is the term used to describe cases where a proteins function at one site is affected by binding of a regulatory molecule at another site.Allosteric regulation may either inhibit or stimulate an enzymes activity. Most allosterically regulated enzymes are made from
multiple polypeptide subunits. Each enzyme has active and inactive forms. The binding of an activator stabilizes the active form
of the enzyme. The binding of an inhibitor stabilizes the inactive form
of the enzyme.
Allosteric enzymewith four subunits
Regulatorysite (oneof four) Active form
ActivatorStabilized active form
Active site(one of four)
Allosteric activatorstabilizes active form.
Inactive form Inhibitor Stabilized inactive form
Allosteric inhibitorstabilizes inactive form.
Allosteric activators and inhibitors
Cooperativity is a form of allosteric regulation that can amplify enzyme activity.In cooperativity, binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits. Binding of one substrate molecule to
active site of one subunit locks all
active site of one subunit locks allsubunits in active conformation.
Cooperativity another type of allosteric activation
Stabilized active formInactive form
In feedback inhibition, the end product of a metabolic pathway shuts down the pathway.Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is neededthan is needed.
Threoninein active site
Isoleucineused up bycell
Feedbackinhibition Active site of
enzyme 1 cantbindth i Intermediate Btheoninepathway off
Structures within the cell help bring order to metabolic pathways.Some enzymes act as structural components of membranes.Some enzymes reside in specific organelles such Some enzymes reside in specific organelles, such as enzymes for cellular respiration being located in mitochondria. Mitochondria,
sites of cellular respiration