What are Inhibitors?
Some molecules are capable of lowering the activity of enzymes by binding with them; such molecules are known as Enzyme Inhibitors. Inhibitors can be used as poisons as well as medicines. Two major types of inhibitors are Competitive and Non-Competitive.

Competitive Inhibition
In competitive inhibition the inhibitor and the substrate compete for placement in the active site of the enzyme. These inhibitors are said to have the same shape to that of the substrate and prevents the enzyme/substrate complex from forming. This is done when the inhibitor enters the active site thus preventing the substrate from entering. Therefore the rate of reaction is decreased due to less substrate molecules binding to the active site. This type of inhibition can be overcome by increasing the substrate concentration.

Competitive Inhibition

Non-Competitive Inhibition
In this form of inhibition the inhibitor does not compete with substrate for a place in the active site but however does reduces enzyme activity by binding to another site on the enzyme known as the Allosteric site. Unlike the competitive inhibition, non-competitive inhibition prevents the formation of products from substrates (enzyme/product complex). Another thing to note about these inhibitors is that they are unaffected by substrate concentration thus most of them are permanent.

Non-competitive Inhibition

Examples of inhibition:
The inhibitor poison malonate can prevent respiration by binding to the enzyme Succinate Dehydrogenase thus preventing succinate from entering the active site by competing with it.

What are Enzymes?


Enzymes are molecules which catalyze chemical reactions. Enzyme molecules are large and globular and possess catalytic properties. Before modern discoveries all enzymes where thought to be proteins, but that belief was dismissed when some where proved to be made of RNA, however most enzymes are proteins. The configuration of an enzyme molecule is as a result of bonding such as hydrogen bonding, ionic bonding, disulphide bridges and hydrophobic interactions.

A Catalyst can alter the rate of a reaction without having itself undergo any permanent change. This therefore means that they can be used more than once.

Enzyme Function


In previous lessons we learned that the activation energy is the minimum energy required for a reaction to take place. Therefore reactions need to exceed their activation energy in order for them to take place. Enzymes reduce this need for activation energy thus allowing reactions to take place more readily.

It also reduces the temperature at which reactions take place thus allowing them to take place at temperatures lower than normal.

The lock and key mechanism refers to the way the substrate molds itself to fit into the active site of the enzyme in the same way a key fits a lock.

Terms you should know: 

Active site: - This is the part on the molecule of an enzyme into which the substrate fits.
Activation energy: - Minimum energy required for a reaction to take place.
Substrate: - The molecule at the beginning of a reaction that is later converted into products.
Specificity: - Enzymes are specific to reactions they catalyze and the substrates involved.

Enzyme Catalyzed Reaction

Metabolism


Chemical reactions are constantly taking place within living organisms this is known as metabolism.
Metabolism can be divided into two groups these are:

1. Anabolism
2. Catabolism

Anabolism Vs Catabolism


Anabolism is simply a phase of metabolism which results in the buildup of simple chemicals into more complex ones while Catabolism is the reverse; it involves the breakdown of complex chemicals into simpler ones.

In spontaneous chemical reactions the products will have a higher entropy that the reactants meaning they will have less free energy. However for chemical reactions to take place an initial input of energy is needed, this initial input of energy is known as the activation energy.

All chemical reactions are said to be reversible; simply put their direction is determined by their conditions. An example of this would be pH, high and low pH can cause reactions to proceed in opposite directions respectively.

Reactions are capable of releasing energy, in biology these are known as exergonic while some can absorb free energy these are known as endergonic.

What is Moments?

By definition Moments, also known as torque, is the turning effect of a force. Moments can either be in a clockwise or anti-clockwise direction. The unit of moments is the Newton Meter (Nm).

Formula for Moments of a force:

      Moments (torque) = Force × Perpendicular distance from the pivot

How to calculate Moments?

Example 1
Find the total moments of the system below:

Diagram Showing Moments

Step 1

Identify which force in the system is moving in the clockwise direction and which is moving in an anticlockwise direction. The 50N force is the one moving in the clockwise direction (the same direction a clock’s pointer would move) while the 80N is moving in the opposite direction (anti-clockwise direction).

Showing Clockwise and Anti-clockwise Moments

Step 2

Use the formula given above to calculate the clockwise and anti-clockwise moments separately.

          Moments = Force × Perpendicular distance

          Clockwise Moments = Force × Perpendicular Distance
                                          = 50N × 6m
                                          = 300Nm

          Anti-Clockwise Moments = Force × Perpendicular Distance
                                                  = 80N × 4m
                                                  = 320Nm

Step 3

Now that you have calculated both clockwise and anti-clockwise moments you can now find the total moments of the system. This is found by subtracting the smaller moments from the larger, in this case the smaller of the two is the clockwise while the larger is the anti-clockwise.

         Total Moments = 320Nm – 300Nm
                                 = 20Nm in the anti-clockwise direction

 Note: Anti-clockwise direction is written at the end because it is larger.

What is Co-ordinate Bonding?

You may have learned about covalent bonding which involves both atoms sharing a pair of electrons; however this is not the case for coordinate bonding. By definition coordinate bonding is a form of covalent bonding in which only one of the atoms share the pair of electrons while the other doesn’t.

Examples of coordinate bonding:

• In the reaction between ammonia and hydrogen chloride a coordinate bond takes place forming solid ammonium chloride. 

                        NH₃ + HCl  ----->  NH₄ Cl

In this reaction the hydrogen ion from the hydrogen chloride leaves its electrons and gets transferred to the lone pair of electrons on the ammonia molecule forming ammonium ions(NH4 +). This is known as a coordinate bonding. Seeing that the hydrogen has left its electrons the chloride will therefore have a negative charge while the ammonium will have a positive charge. The diagram below shows the reaction:

Coordinate bonds are usually represented by using a diagram similar to the one below, the arrow usually points from the atom donating the lone pair to the atom accepting it.

 

• Another example would be the reaction between ammonia and boron trifluoride. Boron trifluoride is said to be electron deficient meaning it has 3 pairs of electrons at its bonding level but it is capable of having four pairs. In this reaction the ammonia is used to supply this extra lone pair. A coordinate bond is formed where the lone pair from the nitrogen moves toward the boron. The end containing the nitrogen will therefore become more positive while the boron end will become more negative because it has received electrons.

 

Resources:

Read more on coordinate bonding at chemguide