8.4 and 8.5 Enzymes speeding up processes and regulation of enzymes

a catalyst

a chemical agent that speeds up a reaction without being consumed by the reaction

an enzyme

biological catalyst

Example of an enzyme

hydrolysis of sucrose by the enzyme sucrase is an example of an enzyme catalyzed reaction

Free energy of activation

activation energy (EA), the initial energy needed to start a chemical reaction

Activation energy is often supplied in the form of

thermal energy that the reactant molecules absorb from their surroundings

Enzymes catalyze reactions

by lowering the activation energy (EA) barrier

enzymes do not

affect the change in free energy, and they cannot make an endergonic reaction

Enzymes speed up reactions that would

eventually occur in the absence of the enzymes

Enzymes are very specific for the

reactions that they catalyze so they determine which chemical processes will be going on in the cell at any given time

the reactant that an enzyme acts on is called

a substrate

when the enzyme binds to its substrate it forms

enzyme substrate complex

the active site

the region on the enzyme where the substrate binds and catalytic reaction occurs

inducted fit

changes the shape of the activation site, by bringing chemical groups within the activation site into positions that enhance their ability to catalyze the reaction

what is this

Induced fit

the change caused by induced fit allows

for additional weak bonds to from causing the active site to enfold the substrate and hold it in place

In what ways does the activation site lower the E_A

• orienting substrates correctly

• straining substrate bonds

• providing a favorable microenviroment

• covalent bonding the substrate

Enzyme activity can be affected by

• temp and pH

• certain chemicals

Cofactors

non protein enzyme helpers that are necessary for activity

Cofactors can be

• inorganic (ionic metals)

• or small organic molecules

coensyme

a cofactor that is an organic molecule

most vitamins

are important because they act as coenzymes or raw materials from which coenzymes are made

Competitive inhibitors

bind directly to the active site and compete with the normal substrate of the enzyme

noncompetitive inhibitors

bind to another part of an enzyme other than the active site, it causes the active site to change shape and makes it less effective

what is happening with the enzymes

competitive inhibition

what is happening with the enzymes

normal binding

what is happening with the enzymes

noncompetitive inhibition

Nearly enzyme produced by the cell

is a protein that is encoded by a gene

Changes in DNA sequencing

lead to a change in the amino acid composition of the enzyme

altered amino acids in enzymes may alter their

substrate specifically

Under new environmental conditions

a new form of an enzyme might be favored over the old form

Chemical chaos

is what would result if a cells metabolic pathways are not regulated

the two ways a cell can regulate metabolic pathways

• switching on or off the genes that encode specific enzymes

  • regulating the activity of enzymes, and controlling the activity of enzymes already produced

Allosteric regulation

can inhibit OR stimulate an enzymes activity

allosteric regulation occurs when

a regulatory molecule binds to a protein at one site and affects the proteins function at another site

Most enzymes involved in allosteric regulation

have a quaterinary structure, more than one poly peptide chain each with there own active site

the enzyme complex oscillates between two different shapes

one catalytically active and the other inactive

binding of an activator molecule

stabilizes the active form of an enzyme

the binding of an inhibitor molecule

stabilizes the inactive form of the enzyme

cooperativity

a form of allosteric regulation that can amplify the response of an enzyme that increases activity

in cooperativity a substrate molecule binding to one active site in a multisubunit enzyme triggers

a shape change in all sub units, and increasing catalytic activity at the other sites

Cooperativity is allosteric

because by binding a substrate to one active site affects catalysis in a different active site

what is this

cooperativity- binding of one substrate to the active site of one subunit locks them all into conformation

what is this

allosteric activator- stabilizes active form, binds to regulatory site

what is this

allosteric inhibitor- stabilizes inactive form

Feedback inhibition

the end product of the metabolic pathway binds and inhibits the function of an enzyme that acts earlier in the pathway

Feedback inhibition prevents

a cell from wasting chemical resources by synthesizing more products than needed

Structures within the cell

help bring order to metabolic pathways

some enzymes act as

structural components of membranes

in eukaryotic cells

some enzymes reside in specific organelles

what type of reaction is this

exergoinic

what is this reactions ∆G

-∆G

what represents the forward reaction of A + B —→ C + D

d, because that is the area where the bonds have broken and are beginning to form into the products, which is the definition of forward reaction

Which of the following represents the activation energy for the enzyme catalyzed A + B → C + D

b, it is the lower of the two activation energies (the humps) because enzymes lower activation energy

which represents the activation energy needed for a reversed enzyme activated reaction C + D → A + B

a, it is the amount of energy required to get to the lower hump (which represents enzyme activation energy)

difference between free energy of reactants and products (in forward or reversed)

d, the free energy of the reactants does not start at the hump (that is activation energy) it instead starts at the line that bisects the graph.

what represents the activation energy for a noncatalyzed (no enzyme) forward reaction

c, it is the larger of the two humps (more activation energy) because without an enzyme the energy does not decrease

what would be the same in an enzyme catalyzed or a non catalyzed forward reaction

d, this is the measure of the difference in free energy at the beginning and end of the reaction, this does not change. The enzymes that help with activation energy do not change free energy

which represents the activation energy needed for the non catalyzed reverse reaction C + D → A + B

e, in order to get over the larger hump (bigger activation energy) from all the way at the bottom with the products you need a lot of energy

cooperativity is specific too

multi subunit enzymes, and it binds to one of the active sites to lock the rest into active