Enzymes

  • Biological catalysts
    • Speed up a chemical rxn ==without being consumed== by the reaction
  • Each enzyme has a ==unique 3-dimensional shape==, and this shape determines ==which rxn it catalyzes==

Enzyme Structure

  • The ==substrate is the reactant== that the enzyme acts on when it ==catalyzes a reaction==

  • The ==product== is the ==end chemical produced==

  • The substrate ==binds to a region on the surface of the enzyme== known as the ==active site==

    • This forms an ==enzyme-substrate complex==
    • It also ==lowers the activation energy==

  • The enzyme and substrate shape ==match== each other exactly

  • Enzymes are ==specific== since ==only one enzyme acts on only one substrate==

  • Once the substrate is catalyzed, the enzyme takes its original form and can be reused

Types of Reactions

  1. Degradation Reaction (‘breaking down’)
  2. Synthesis Reaction (building up)

Degradation Rxn

Lock and Key

  • The substrate and enzymes active site are ==complementary shapes==

Induced Fit Hypothesis

  • Enzymes are ==not rigid objects==, like locks, but they are ==flexible==
  • The enzyme ==changes its shape== (conformation) prior to substrate binding so that the active site becomes ==even more precise in its ability to bind to its substrate==
    • This is the ==induced-fit model==
  • An enzyme binds to ==one or more substrates==, forming an ==enzyme substrate complex==
  • The enzyme then converts the substrate into ==one or more products==, and since enzymes stay ==unchanged== after a rxn, enzyme molecules can ==rapidly bind to other substrate molecules==, catalyzing the same rxn repeatedly

Factors Affecting Enzyme Activity

  • Enzyme concentration
  • Temperature
  • pH

Enzyme and Substrate Concentration

Enzyme Concentration

  • ==Increasing enzyme [ ]== will ==speed up the reaction==, as long as there is ==substrate available to bind to==
  • Once all of the substrate is bound, the rxn will ==no longer speed up==, since there will be nothing for addition enzymes to bind to

Substrate Concentration

  • ==Increasing substrate [ ]== also ==increases the rate of rxn== to a certain point

  • Once all of the enzymes have bound, any substrate increase will have ==no effect on the rate of rxn==, as the available enzymes will be ==saturated== and ==working at their max rate==

Temperature

  • As ==temp increases==, ==enzyme activity increases==
  • The temp that the enzymes work best at is called its ==optimum temperature==
  • If the temp is ==too high==, the enzymes active site ==changes shape==
  • When the enzymes active site has changed shape, the enzyme is said to be ==denatured== and it ==will no longer work==
  • For enzymes in human cells, the optimal temp is usually around ==human body temp== (37.5)

pH

  • Enzymes work best within a ==range of pH== depending on the type of enzyme
  • The pH that the enzymes work best at is called ==optimum pH==
    • This is usually around a ==pH of 7==
  • If pH is too ==high==, enzyme active site ==changes shape== (denatured)

Enzyme Activators

  • Enzyme activators are molecules that ==bind to an enzyme== and ==turn them on== in a chemical rxn cofactors
  • Types of enzyme activators include:
    • Cofactors
    • Coenzymes

Cofactors

  • ==Inorganic==, ==non-protein group== that ==binds to an enzyme== and is ==essential for catalytic activity==
  • Most often ==metals== (iron, copper, zinc, and manganese) are cofactors

Coenzymes

  • ==Organic==, ==non-protein molecules== that ==act like cofactors==
  • They act as ==electron transport carriers== during ==biochemical pathways==
  • Both cofactors and coenzymes can ==bind to either the substrate or the active site== of the enzyme

Enzyme Inhibitors

  • Enzymes need to be ==regulated== to ensure that levels of the product don’t rise to ==undesired levels==, and this is accomplished by ==enzyme inhibition==
  • Enzyme inhibitors are ==molecules that binds to an enzyme== and ==turn them off in a chemical rxn==
  • Types of inhibitors include:
    • Competitive inhibitors
    • Non-competitive inhibitors
  • Reversible and irreversible inhibitors are ==chemicals which bind to an enzyme== to ==suppress its activity==
    • ==Irreversible inhibitors== almost ==permanently bind to an enzyme==
    • ==Reversible inhibitors== are ==chemicals that transient bind to an enzyme==, either to an ==active site (competitive inhibitor)== or to ==another site on the enzyme (non-competitive inhibitors)==
  • ==Competitive== inhibitors are so ==similar== to an ==enzyme’s substrate== that they can ==bind to the active site== and ==block the normal substrate==
  • ==Non-competitive== inhibitors ==bind to the enzyme== at an ==allosteric site (not the active site)== and cause a ==conformational change in the enzyme==, preventing the normal substrate from binding

Allosteric Control of Enzyme Activity

  • The allosteric site is a binding site on an enzyme that ==binds regulatory molecules==
    • Either ==activate== or ==inhibit==, or turn off, ==enzyme activity==
  • These molecules ==bind the allosteric site== and ==change the conformation, or shape, of the enzyme==
  • ==Allosteric regulation== is the regulation of one site of a protein ==binding== to another site on the same protein

Allosteric Regulation

  • In allosteric inhibition, the active site ==changes shape== when an inhibitor ==binds to an allosteric site==

  • In ==allosteric activation==, the activators ==may bind to allosterically controlled enzymes== to st==abilize its shape== and keep all active sites available

Feedback Inhibition

  • Occurs when there is a ==sequence of chemical rxns== that are ==forming a common product in the end==

  • When the product ==travels back== and ==inhibits an earlier enzyme== in the rxn (competitively or non-competitively) the pathway is ==interrupted== and no more product is made

Uses of Enzymes