ENZYMES – Nature’s Catalysts Done by: Azizul, Izzah and Fatin
ENZYMES – Nature’s CatalystsDone by: Azizul, Izzah and
Fatin
What Are Enzymes ?• Enzymes are Proteins.
(Tertiary and Quaternary)
• Act as catalyst to accelerate a reaction.
• Not permanently changed in the process.
• Enzymes are specific, will only catalyse one particular reactions.
How Do Enzymes Work ?
Enzymes work by weakening the bonds which lowers the activation energy.
FREEENERGY
} ACTIVATION ENERGY
REACTANTS
PRODUCTS REACTION PATHWAY
How Do Enzymes Work ?Without Enzyme
With Enzyme
A restricted region of an enzyme molecule which binds to the substrate.
The shape and the chemical environment inside the active site permits a chemical reaction to proceed more easily.
The Active Site
© H.PELLETIER, M.R.SAWAYA ProNuC Database
An additional non-protein molecule that is needed by some enzymes to help the reaction.
Tightly bound cofactors are called prosthetic groups
Cofactors that are bound and released easily are called coenzymes
Vitamins are most likely coenzymes.
COFACTORS
Nitrogenase enzyme with Fe, Mo and ADP cofactors
The substrate of an enzyme are the reactants that are activated by the enzyme
Enzymes are specific to their substrates The specificity is determined by the
active site
THE SUBSTRATE
Fit between the substrate and the active site of the enzyme is exact
Like a key fits into a lock very preciselyThe key will be the enzyme and the substrate
will be the lock. Temporary structure called the enzyme-
substrate complex formed Products have a different shape from the
substrate Once formed, they are released from the active
site Leaving it free to become attached to another
substrate
THE LOCK AND KEY HYPOTHESIS
THE LOCK AND KEY HYPOTHESIS
S
E
P
P
Enzyme-substrate complex
Reaction Pathway
Free Energy
1. The enzyme is surrounded by variously shaped substrate molecules.
2. The enzyme is capable of changing the shape of the active site slighty to accomodate for the substrate and ultimately form an Enzyme-Substrate Complex.
3. The enzyme breaks down the substrate into smaller pieces.4. The enzyme then releases the substrate and the active site
then returns to its original shape, ready to bind to more substrate molecules.
The Induced-Fit Hypothesis
The are 6 factors: 1. Temperature 2. pH 3. Enzyme Concentration 4. Substrate Concentration 5. Presence of Inhibitors 6. Presence of Cofactors
What Affects Enzyme Activity ?
Increasing the temperature, - double the reaction - more collisions between particles but only up to optimum temperature. (c) As temperature increases ( >c), more bonds, especially
the weaker Hydrogen and Ionic bonds, will break as a result of this strain. Breaking bonds within the enzyme will cause the Active Site to change shape.
This change in shape means that the Active Site is less Complementary to the shape of the Substrate, so that it is less likely to catalyse the reaction. Eventually, the enzyme will become Denatured and will no longer function.
1. Temperature
40
Temperature En
zym
eA
ctiv
ity
Temperature
OPTIMUM TEMP.
Extreme pH levels will produce denaturation The structure of the enzyme is changed The active site is distorted and the substrate
molecules will no longer fit in it At pH values slightly different from the enzyme’s
optimum value, small changes in the charges of the enzyme and it’s substrate molecules will occur
This change in ionisation will affect the binding of the substrate with the active site.
2. pH
pH
3 119751
Trypsin
Pepsin
Optimum pH values
pH
Enzyme activity
5. Presence Of InhibitorsA substrate that can slow down or stop
an enzyme controlled reaction – they combine with the enzyme and stop the substrate attaching to it.
Can be reversible and non-reversibleThere are two types of inhibitors:-
Competitive InhibitorsNon-Competitive Inhibitors
Competitive inhibitorsHas a structure that similar to that of the
substrate and so compete with the substrate for the active site.
As a result, it will reduce the no. of enzyme substrate complexes and so reduce the reaction rate.
This type of inhibition is reversible by an increase in substrate concentration: eventually allow substrate to bind.
So the more substrate available, the less inhibitor will bind its active site.
Non-Competitive InhibitorsDoes not compete for active site.
It attached to another part of enzyme causing the overall shape of the enzyme molecules to change.
Changes the shape of the active site so substrate can no longer bind.
Increasing the amount of substrate will not reduce this inhibitors since there are not in competition for active site.
Removal of inhibitor will restore normal shape of the enzymes.
Irreversible InhibitorsSome inhibitors bind irreversibly to an
enzyme and so destroy its catalytic properties completely.
Usually poisonous to the cells because they close down some part of the metabolism.
Are always non competitive inhibitors.
6. Presence Of Co-FactorsOther small molecules can improved the
action of enzymes, sometimes enzymes will not work without them.
These substances are called Co-factors.Substances derived from vitamin can often
act as Co-factors, in some cases just improving the action of enzymes.
E.g: Carbonic Anhydrase. Has an Zn2+ as an active site. Without them, the enzyme will not work.