Welcome back folks, we did enzymes part 1, now it’s on to part 2.
To start off let’s continue with the features of enzymes. The catalytic power of enzymes was dealt with in part 1, so we will now focus on the specificity of Enzymes.
Try not to bite your tongue saying SPECIFICITY!!!!!
SPECIFICITY OF ENZYMES
A certain enzyme, is one that is very selective, we can also say that they are “picky” or “stush”. They are very selective on what substance they react with and also in the reaction they catalyse.
The substances that the enzymes work on are what we call SUBSTRATES.
Also, in a reaction where an enzyme is present, or, an enzyme catalysed reaction, there are NO by products, or waste products and all reactions tend to yield a great percentage of product.
The products that are formed from an enzyme catalysed reaction are also “stush enzymes”.
In the chemical reaction involving enzymes, the substrate, has to stick or bind to the enzyme by a process called MOLECULAR RECOGNITION.
All this is saying is that the substrate compliments or suits the enzyme perfectly, it’s like a match made in heaven. Like peanut butter and jam, like ice-cream and cake, like biology and chemistry. This way, they form a mutual relationship, they both benefit from each other.
The substrate binds to a specific area on the enzyme called THE ACTIVE SITE.
So, let’s talk about this active site!!!!!!!!!!!!!!!!!!!!!!
The active site is a pocket or cleft that is made to recognize certain substrates and thus, catalyse chemical transformation.
It is formed in the 3D structure by the group of a variety of Amino Acid residues. These Amino Acid residues are either adjacent or not in the primary formation.
At the ACTIVE SITE, the substrate associates or mingles with the active site via hydrophobic, electrostatic, hydrogen and Vanderwaal’s interactions. These are the same forces that cause the structure of protein to be stable and they are all weak forces of attraction.
The active site of enzymes can also, provide catalytic groups. These groups are the “R” groups of Amino Acids residues and they give certain interactions and allow chemistry which stabilizes the transition state form for the chemical reaction to occur.
When a substrate binds together with an enzyme at the active site by the weak forces we discussed above, a complex is formed. This complex is called THE ENZYME SUBSTRATE COMPLEX.
There are different Hypotheses models to explain how enzymes are catalytic and specific.
The two major ones are:
- THE FISCHER’S LOCK AND KEY HYPOTHESIS
- THE KOSHLAND’S INDUCED FIT HYPOTHESIS.
Let’s talk about Fischer’s hypothesis first; it implies the lock and key method.
Look at the figure below!!!
In the diagram, we can clearly see that the key is analogous to the substrate, while the lock is the enzyme. The key fits into the lock perfectly. In the same way, the substrate fits into the enzyme perfectly forming the enzyme substrate complex. There shape coincides so the complex is formed. If however, another substrate was to try to fit into the active site of this enzyme, the complex would not be formed since the substrate doesn’t match the enzyme’s active site.
In the same way, my car keys can only start my car, if I were to try to start someone else’s car with my keys nothing would happen because they DO NOT MATCH.
The product that is formed, is different from that of the substrate in terms of shape, thus, it is unable to fit into the active site and is released for another substrate of the same shape to bind to the active site once again.
THE INDUCED FIT HYPOTHESIS!!!!!!!!!!!!!!
This hypothesis is self explanatory. The fit of the substrate to the active site is induced. Initially, it does not have a perfect fit; however, as the substrate is brought towards the active site or is on its way to the active site, it induces its shape into the enzyme. The active site now becomes an exact fit when the substrate is in the active site of the enzyme.
The products formed, also have a different shape so they are set free for more substrates to enter.
The diagram below shows the Induced Fit hypothesis:
THE FACTORS AFFECTING REACTION RATE OR REACTION VELOCITY.
There are a number of factors that can affect the rate of reaction velocity, involving enzymes that is. They include:
- Ø Substrate concentration
- Ø Enzyme concentration
- Ø Temperature
- Ø pH
In the graph above, the main focus is on the blue line known as Michaelis Menden curve. At first, as substrate concentration increases, reaction rate increases steadily. This is because; there are more collisions between substrates and the active site, more effective collisions. The point at which the line plateau or levels off, is the point where saturation level has been reached.
That is, the amount of substrate level is continuously increasing but there are no more active sites available so they have to wait on the next available active site. The reaction is still in process; however, the rate is not increasing. In this illustration, the only variable is the substrate concentration. Temperature, enzyme concentration and pH are kept constant.
References for Images: