6.5 Enzymes and the Rate of Chemical Reactions Flashcards Preview

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Flashcards in 6.5 Enzymes and the Rate of Chemical Reactions Deck (52)

chemical reaction in a cell are accelerated by:

chemical catalysts


the rate of a chemical reaction is defined as:

the amount of product formed (or reactant consumed) per unit of time


catalysts are:

substances that increase the rate of chemical reactions without themselves being consumed



a protein that functions as a catalyst to accelerate the rate of a chemical reaction; enzymes are critical in determining which chemical reactions take place in a cell


because enzymes are highly specific, acting only on certain reactants and catalyzing only some reactions, enzymes play:

a critical role in determining which chemical reactions take place from all the possible reactions that could occur in a cell


all chemical reactions require:

an input of energy to proceed (ever exergonic reactions)


if exergonic reactions release energy? how does that explain why the chemical reactions require an input of energy?

the energy released is more than the initial input of energy, so there is a net release of energy


transition state

the brief time in a chemical reaction in which chemical bonds in the reactants are broken and new bonds in the product are formed


the transition state is highly unstable and therefore has a large amount of ...

free energy


in all chemical reactions, reactants adopt at least one:

transition state before their conversion into products


all chemical reactions, even spontaneous ones that release energy, require:

an input of energy : think of an "energy barrier"


activation energy

the energy input necessary to reach the transition state


there is an inverse correlation between the rate of a reaction and:

the height of the energy barrier (ex. lower energy barrier = faster reaction)


what is used to overcome the energy barrier in labs?

heat as a source of energy


in living organisms, reactions are accelerated by:



how do enzymes accelerate chemical reactions in organisms?

they reduce the activation energy by stabilizing the transition state and decreasing its free energy. (as the activation energy decreases, the speed of the reaction increases)


as the activation energy decreases....

the speed of the reaction increases


even with the presence of an enzyme, what doesn't change?

the difference in free energy between reactants and products (delta G)


an important characteristic of enzymes is that, as catalysts, they:

participate in a chemical reaction but are not consumed in the process (remain unchanged)


how do enzymes increase the reaction rate without being consumed?

enzymes form a complex with the reactants and products


substrate (S)

a molecule acted upon by an enzyme; AKA the reactant


describe the process of the enzyme in a chemical reaction

substrate forms a complex with the enzyme (enzyme-substrate) which is converted to product (enzyme-product), while complex dissociates, enzyme and product is released


S+E =



proteins adopt three-dimension shapes and the shape of a protein is linked to:

its function


active site

the portion of the enzyme that binds substrate and converts it to product


in the active site, the enzyme and substrate form:

transient covalent bonds and/or weak non covalent interactions. these interactions stabilize the transition state and decrease the activation energy


enzymes reduce the energy of activation by:

positioning two substrates to react


the formation of the enzyme-substrate complex promotes:

the reaction between two substrates by aligning their reactive chemical groups and limiting their motion relative to each other


the active site is very small in comparison to the entire enzyme, why is the enzyme so large then?

the large size of many enzymes is required to bring the catalytic amino acids into very specific positions in the active site of the folded enzyme (specific amino acids have to align correctly with the reactive group of the substrate)


in many cases, the catalytic amino acids (which form the active site) are spaced far apart in the primary structure of the enzyme and brought close together:

in the formation of the active site by protein folding


enzymes are remarkably specific for both the:

substrate and the reaction that is catalyzed: enzymes recognize either a unique substrate or a class of substrates that share common chemical structures; enzymes catalyze only one reaction or a very limited number of reactions


in some cases, the enzyme does not recognize the whole substrate but a particular:

structural motif within it, and very small difference in the structure of this motif affect the activity of the enzyme


the enzyme is able to discriminate between two identical bonds with:

different orientations within a molecule


the specificity of enzymes can be attributed to:

the structure of their active sites; the enzyme active site interacts only with substrates having a precise 3D structure


what can influence the activity of enzymes?

inhibitors and activators



a synthesized compound that decreases the activity of an enzyme



a synthesized compound that increases the activity of an enzyme


enzyme inhibitors are quite common because they are synthesized:

naturally by many plants and animals as a defence against predators


what are some of the other uses of an enzyme inhibitor?

pesticides/herbicides often target enzymes to inactivate them, drugs used in medicine; infections/cancer/other diseases


what are the two classes of inhibitors?

irreversible inhibitors and reversible inhibitors


irreversible inhibitors

usually form covalent bonds with enzymes and irreversibly inactivate them


reversible inhibitors

form weak bonds with enzymes and therefore easily dissociate from them


the inhibitor competes with the substrate for the active site of the enzyme:

binding of the inhibitor prevents the binding of the substrate


inhibitors that compete with the substrate for the active site can be overcome by:

increasing the concentration of the substrate


another case of inhibitors is that they change the:

shape and activity of the enzyme by binding to a site (not the active site); this type of inhibitor has a structure very different from that of the substrate


what are the two mechanisms of inhibitor function?

some inhibitors bind to the active site, some bind to a different site. both types reduce the activity of an enzyme and the rate of the reaction


allosteric enzyme

an enzyme whose activity is affected by binding a molecule at a site other than the active site. typically, allosteric enzymes change their shape on binding an activator or inhibitor


enzyme activators and inhibitors are sometimes important in the:

normal operation of a cell (ex. regulation of a metabolic pathway)


negative feedback

describes the effect in which the final product of a biochemical pathway inhibits the first step; the process in which a stimulus acts on a sensor that communicates with an effector, producing a response that opposes the initial stimulus. Negative feedback is used to maintain steady conditions, or homeostasis



a substance that associates with an enzyme and plays a key role in its function (ex. metal ions in enzymes)


what naturally occurring elements might have spurred the first reactions that led to life?

metal ions by themselves can catalyze chemical reactions


what has been proposed as the evolutionary descendants of chemical reactions that took place spontaneously on the early Earth?

the reactions now carried out in cells by iron-sulfur proteins (similar to the reactions in ancient hydrothermal environments)