Topics 3.6 and 7.6. the amount of energy released is greater than the activation energy Energy released.

topics 3.6 and 7.6

               the amount of energy released is greater than the activation energy

Energy released

the amount of energy released is less than the activation energy

Energy must be supplied

• Biological catalysts

• Proteins

• Specific A substance that speeds up a chemical reaction without being used up in the reaction

Every reaction involves breaking bonds, that requires energy. The rate of a particular reaction depends on the activation energy necessary to initiate it.

Catalysts reduce the activation of energy increasing reaction rates.

1894 - chemist Emil Fischer. Proposed the lock and key model.

KEY (substrate) has a specific shape (arrangement of functional groups and other atoms) that allows it and no other key to fit into the LOCK (the enzyme).

LOCK AND KEY MODEL

The substrate and enzyme complement each other

Therefore, they can fit together, like a lock and key.

Different molecules do not complement the enzyme's active site.

INDUCED FIT MODEL

1958 - Daniel E. Koshland Jr. modified the lock-and-key model

He proposed that binding of the substrate to the enzyme alters the configuration of both, providing a better fit.

Before binding, the substrate and enzyme do not exactly fit each other

Binding of the substrate to the enzyme changes the configuration of both so that they fit together. Different molecules

cannot induce a fit with the enzyme

Increase substrate or enzyme concentration…Molecules more likely to collide…More reactions…Rates of reaction increases…Up to a point where the rxn reaches a maximum – saturation point.

Increasing temperature –

Increases molecular movement …

more likely for enzyme and substrate molecules to meet…

Increases reaction rate.

Low temp: H-bonds and interactions that give the enzyme its shape aren’t flexible enough to permit the induced fit for optimum reaction rates

High temp: H-bonds and interactions are too weak to maintain enzymes shape due to increased movement of atoms making up the enzyme

Enzymes function at an optimum pH

Changing pH results in a change of balance of the hydrogen ion concentration and therefore the balance between positively and negatively charged amino acids making up the enzyme

Changes in the charges of the aa’s results in a change in the shape of the enzyme

Different enzymes have different optimal pH’s

Denaturation = a structural change in a protein that results in a loss (usually permanent) of its biological properties.

When exposed to high temperature or extremes of pH

Enzyme activity can be inhibited which slows the rate of reaction

Competitive inhibition

Noncompetitive inhibition

Examples of inhibitors….

Aspirin, Ibuprofin, DDT, Sarin nerve gas, Penicillin

Protease inhibitors as a possible cure for AIDS

Inhibiting molecule is structurally similar to the substrate

It binds to the active site preventing the substrate from binding

Enzyme inhibition

This antibiotic binds to active site of glycoprotein peptidase, an enzyme that forms the peptide bonds in peptidoglycan, a component of the bacterial cell wall (so is a competitive inhibitor.)

With a weaker cell wall, bacteria are more susceptible to rupture by osmotic lysis and so fail to survive

Penicillin G Penicillin V

Allosteric Inhibition –

Inhibitor molecule binds to enzyme (not the active site)

Causes a conformational change to active site

Resulting decrease in activity

Regulates metabolic pathways thru end product inhibition

Inhibits the enzyme acetyl-cholinesterase, an enzyme in the body that plays a critical role in maintaining nerve function and control. 

When the enzyme is inhibited, a build-up of acetylcholine occurs at the nerve endings, causing symptoms that include blurred vision, profuse sweating and loss of motor function control.  Paralysis many times follows.  

Enzyme Group Type of reaction catalyzed Examples

Oxidoreductases Transfer of O & H atoms between substances, ie. all oxidation-reduction reactions

DehydrogenasesOxidases

Transferases Transfer of a chemical group from 1 substance to another TransaminasesPhophorylases

Hydrolases Hydrolysis reactions PeptidasesLipasesPhosphatases

Lyases Addition or removal of a chemical group other than by hydrolysis

Decarboxylases

Isomerases The rearrangement of grops within a molecule IsomerasesMutases

Ligases Formation of bonds between 2 molecules using energy derived from the breakdown of ATP

Synthestases

• Start with the name of the substrate upon which the enzyme acts, ie. succinate

• Add the name of the type of the reaction which it catalyzes, ie. dehydrogenation

• Convert the end of the last word to an –ase suffix, ie. dehydrogenase

• Thus: succinic dehydrogenase