Enzymes and thermodynamics


Energy has the potential to do work. Potential energy is energy which is being stored. This can be the energy between atoms stored in chemical bonds. If these chemical bonds are broken and energy is released this takes the form of kinetic energy. Kinetic energy is the energy something posses due to it having motion. Heat is an example of kinetic energy since the motion of particles vibrating is what creates heat.

The first law of thermodynamics states energy can’t be created or destroyed just changed from one for to another. The second law states that the universe is heading towards becoming more disordered (increasing entropy).

However, living things can create incredibly ordered structures through applying energy to become more ordered. This requires the input of energy.

When chemical species are placed in a beaker, they will reach equilibrium. I.e there will be a certain ratio of products to reactants. This ratio occurs when the energy of the reactants is equal to the energy of the products.

The activation energy is the amount of energy required to be put into a system in order for a reaction to occur. A reaction occurs when reactants collide with sufficient kinetic energy in a favorable orientation. This successful collision results in a chemical reaction. Hence heating a solution increases the kinetic energy of molecules resulting in more successful collisions occurring per unit. As a result more reactions occur since there are more reactants with sufficient kinetic energy to get over the activation barrier.

Alternatively, an enzyme can be used which lowers the activation barrier allowing increasing the rate of reaction. A catalyst is a compound which is not used up in a chemical reaction and increases the rate of reaction hence an enzyme is a type of catalyst.

Living things can’t wait hundreds of years for a chemical reaction to occur. Additionally, most organisms need to be at 0 – 50 degrees Celsius to live. This means they need a solution. Living things create enzyme which are proteins encoded in their DNA.

Enzymes bind with substrates (reactants) at the active site of the enzyme. This is a very precise bond which was first explained with the lock and key model. However, later models followed such as the induced fit which stated the active site of the enzyme changed when the substrate binded to it – locking it in place. While the later model, the selection model, states enzymes shapes are changing and are in equilibrium. When a certain orientation is achieved, the substrate binds to the enzyme, resulting in more enzymes changing to that shape (Le Chatelier’s principles) hence more substrates bind to enzymes.

In order for enzymes to function they have certain conditions which allow them to work at optimum performance. Temperature, pH and concentration of substrate and enzyme all affect enzymes optimum performance. Co factors may also be required for an enzyme to function. However, an inhibitor can prevent an enzyme from functioning normally. An inhibitor can act through binding to the active site or to another part of the enzyme (allostery) inhibiting function.

In living things, enzymes form complex pathways which have multiple catalyzed steps.

As previously stated, nucleic acid form phosphodiester bonds which are thermodynamically unfavorable. Hence bonding of neucleotides to aminoacids results in the release of the diphosphate group. By having a pyrophosphate enzyme rapidly catalyse the diphosphate group it prevents the reverse reaction and the large energy output makes the total reaction thermodynamically favourable.



Question 1.

Contrast potential and kinetic energy.

Question 2.

Explain how living things are able to fight entropy.

Question 3.

How do enzymes work and why/ why don’t they affect the position of equilibrium

Question 4.

How can secondary reaction drive a primary thermodynamically unfavorable reaction – use an example

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