Enzymes Flashcards
Enzyme structure
enzymes, being globular proteins, have a specific 3-D shape that is the result of their sequence of amino acids A specific region of the enzyme is functional, this is known as the active site. The active site is made up of a relatively small number of amino acids. The active site forms a small depression within the much larger enzyme
The molecule on which the enzyme acts is called the substrate. This fits neatly into this depression and forms an enzyme-substrate complex (. The substrate molecule is held within the active site by bonds that temporarily form between certain amino acids of the active site and groups on the substrate molecule
Induced fit
the enzyme is flexible and can mould itself around the substrate The enzyme has a certain general shape,but this alters in the presence of the substrate. As it changes its shape, the enzyme puts a strain on the substrate molecule. This strain distorts a particular bond or bonds in the substrate and consequently lowers the activation energy needed to break the bond.
Temp on enzyme activity
A rise in temperature increases the kinetic energy of molecules. As a result, the molecules move around more rapidly and collide with each other more often. In an enzyme-catalysed reaction, this means that the enzyme and substrate molecules come together more often in a given time. There are more effective collisions resulting in more enzyme-substrate complexes being formed and so the rate of reaction increases.
What is denatureation
Denaturation is a permanent change and, once it has occurred, the enzyme does not function again.
Effect of ph
• A change in pH alters the charges on the amino acids that make up the active site of the enzyme. As a result, the substrate can no longer become attached to the active site and so the enzyme-substrate complex cannot be formed.
• Depending on how significant the change in pH is, it may cause the bonds maintaining the enzyme’s tertiary structure to break. The active site therefore changes shape.
The arrangement of the active site is partly determined by the hydrogen and ionic bonds between —NH, and —CoOH groups of the polypeptides that make up the enzyme. The change in H* ions affects bonding, causing the active site to change shape.
Low enzyme concentration
There are too few enzyme molecules to allow all substrate molecules to find an active site at one time. The rate of reaction is therefore only half the maximum possible for the number of substrate molecules available.
Intermediate enzyme conc
With twice as many enzyme molecules available, all the substrate molecules can occupy an active site at the same time.
The rate of reaction has doubled to its maximum because all active site are filled.
High enzyme conc
The addition of further enzyme molecules has no effect as there are already enough active sites to accomodate all the available substrate molecules. There is no increase in the rate of reaction.
Low substrate concentration
There are too few substrate molecules to occupy all the available active sites. The rate of reaction is therefore only half the maximum possible for the number of enzyme molecules available.
Intermediate substrate concentration
With twice as many substrate molecules available, all the active sites are occupied at one time. The rate of reaction has doubled to its maximum because all the active sites are filled.
High substrate concentration
The addition of further substrate molecules has no effect as all active sites are already occupied at one time. There is no increase in the rate of reaction
Competetive inhibitors
inhibitors have a molecular shape similar to that of the substrate. This allows them to occupy the active site of an enzyme.
They therefore compete with the substrate for the available active sites). It is the difference between the concentration of the inhibitor and the concentration of the substrate that determines the effect that this has on enzyme activity. If the substrate concentration is increased, the effect of the inhibitor is reduced. The inhibitor is not permanently bound to the active site and so, when it leaves, another molecule can take its place. This could be a substrate or inhibitor molecule, depending on how much of each type is present. Sooner or later, all the substrate molecules will occupy an active site, but the greater the concentration of inhibitor, the longer this will take.
Non competitive inhibitors
Non-competitive inhibitors attach themselves to the enzyme at a binding site which is not the active site. Upon attaching to the enzyme, the inhibitor alters the shape of the enzyme and thus its active site in such a way that substrate molecules can no longer occupy it, and so the enzyme cannot function. As the substrate and the inhibitor are not competing for the same site, an increase in substrate concentration does not decrease the effect of the inhibitor
