Enzymes

Enzymes

CHARACTERISTICS

* Molecule has a active site

* Changes in ph and temperature can adversely change enzyme action

* Increase rate of reaction i.e. acts as a catalyst

* All processes are reversible

* Protein molecules well developed tertiary structures

* Specific

Remember in order to start a reaction a certain amount of energy has to be supplied called activation energy.

STRUCTURE

Enzymes are globular proteins; this means they are very complex

LOCK AND KEY

The enzyme provides the substance with a specific part where it can fit to form an enzyme substrate complex.

INDUCED FIT

Shows that the enzyme-substrate complex as being more flexible - in that the substrate molecules changes shape of enzyme molecule as the enzyme substrate complex formed.

HOW THEY WORK?

* There is similarities between enzyme and the active site

* Electrostatic bonds used to establish the enzyme substrate complex.

* Some enzymes have non-protein parts which are necessary for enzyme action

* These are called Co-factors, which are three of them inorganic ions. Prosthetic groups and co-enzymes

WHAT IS A CO-FACTOR?

* Some aspect over and above the enzyme which is needed for the enzyme to work

* In some cases: enzyme + co-factor are needed for enzyme action.

INORGANIC IONS

Around the enzymes helps do its job

* They mainly influence shape of enzyme molecule e.g. Cl‾ is needed for salivary amylase. Many trace elements can fulfil its role e.g. Zinc, Copper.

PROSTHETIC GROUPS

* Similar to co-enzyme

* Usually act as carriers during enzyme controlled metabolic change

CO-ENZYMES

* Very similar but loosely attached to the enzyme molecule

TEMPERTURE

* If temperature goes above a certain level the vibration will break some of the bonds that hold the enzyme

* Active site changes so no longer fit

* At this enzyme denatures

GRAPH OF RATE OF REACTION

The steep declines after an optimum

* At low temperatures, enzymes are inactivated rather then denatured ( the extent is dependent on time)

* In enzyme experiments, remember technique of equilibration i.e. allowing enzyme & substrate to reach a desired temperature separately.

PH AND ENZYME ACTION

Shape of graph is symmetrical, more bell- shaped.

WHY? HOW? Does PH affect enzyme activity?

* Ph affects the ionisation of side groups in amino acid residue

* In extreme case Ph can denature enzymes

* Can switch it on of off as sometimes enzymes not surrounded by its optimum temperatures

SUBSTRATE CONCENTRATION ON RATE OF ENZYME ACTION

* Affects the rate of reaction up to certain point

* The higher the substrate concentration the faster the reaction but only up to saturation point

* After that there is too much substrate molecules enzyme can cope with.

REVERSIBLE INHIBITION

This is when inhibition may be easily removed

* Competitive reversible inhibition. This is described as active site directed inhibition. Here there is shape similarities between substrate and the inhibitor, they are so similar that the inhibitor occupies the active site prevents the substrate from doing so and therefore lowers the rate.

How could you reduce the affect of active site directed inhibitor? By increasing the concentration of true substrate.

* Non competitive or non active site directed inhibition

Inhibitor binds to the allosteric site (alternative site) changing shape of active site.

INCREASED ENZYME CONCENTRATION

* The more enzyme molecule, the more likely the substrate is to collide. So increases in rate.

* But