Enzymes

Enzymes

Enzymes are biological catalysts that carry out thousands of chemical

reactions that occur in living cells. They are a class of proteins

that have a unique three dimensional structure that allows it to bind

with a specific substrate to facilitate a

reaction. Many biological reactions will not occur spontaneously in

the cell; there is simply not enough energy for the reaction to take

place. Enzymes make these

reactions possible by lowering the reactionÂ’s activation energy. Each

cell has tens of thousands of different enzymes that collectively

allow both the break down and synthesis of molecules to drive all

cellular processes.

This investigation will explore the effect of pH on the

three-dimensional structure of a protein. Much of the

three-dimensional structure of an enzyme is held together by

weak interactions including H-bonds, ionic bonds, and hydrophobic

interactions.

These interactions can be easily disrupted by changes in temperature,

salt

concentration, and pH. pH levels out of the normal intracellular range

would

denature enzymes, slowing the enzymeÂ’s reaction rates.

Hydrogen peroxide (H2O2) is a toxic chemical that is continually being

formed as

By product of reactions in peroxisomes of living cells. Since it is

poisonous, the cells

must either get rid of it or change it to something nonpoisonous. If

they cannot do

this, the cell may die; catalase solves this problem. The enzyme

catalase is found in animal and plant tissues, and is especially

abundant in plant storage organs such as potato tubers, corns, and

fleshy part of fruits. Catalase reacts with the H2O2 to fo...

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...O and -NH3+. At high pH

the predominant forms will be -COO- and -NH2. However the actual pH at

which each group becomes ionised depends on the particular amino acid

and also the environment in which the enzyme is found. The usual way

of expressing this is the pK value: this pK is the pH at which half of

the groups are ionised.

Interactions between these positive and negative charges are a very

important part of what holds the structure together in an enzyme.

These links are known as salt links, salt bridges or electrostatic

interactions and involve a + to - attraction. Changing the pH

therefore alters the properties of these salt bridges. Even a small

shift away from optimum pH might mean one of these salt bridges is

affected and therefore the shape and activity and stability of the

protein will also be affected.