A substrate is substance on which enzymes acts to covert into a product.
For many enzymes, there is only one specific substrate. But most enzymes have two or more substrates.
A substrate is very specific for an enzyme to catalyze the reaction. It means a substrate can be broken down in presence of that specific enzyme. It cannot undergo chemical change by other enzymes.
What is a substrate role in enzyme reaction.
- An enzyme catalyzes a reaction only in the presence of a substrate.
- Increase in substrate concentration can enhance the reaction rate.
- The rate of reaction reaches peak when the enzyme is saturated by the substrate.
How does substrate enzyme interaction occurs?
A substrate (S) binds to the active site of an enzyme (E) to form an enzyme substrate complex. The enzyme will remain unchanged while the substrate gets broken down to products. This is given as a reaction below.
S + E <========>ES <===========> E + S.
Examples of substrates:
1. Carbohydrates like glucose, sucrose, starch act a substrates for enzymes like salivary amylase, maltase
2. Amino acids, peptides, proteins act as substrates for enzymes trypsin, chymostrypsin etc.
These proteins are found in grams, meat we eat.
3. Fatty acids act as substrate for lipase enzyme. Fats are obtained from food and by synthesis in the body.
4. Nucleic acids DNA and RNA are substrates for nuclease enzyme.
5. Ethyalcohol is broken down by the enzyme alcoholdehydrogenase.
When substrate concentration is increased, the reaction rate is enhanced. This is because there are more number of substrate molecules ready to undergo biochemical reaction. However, this enhancement of reaction is limited. After all the active sites of the enzyme are occupied by substrate, there will no further increase in rate of reaction.
So, remaining substrate molecule have to wait till the previously bound molecules are broken down and removed.
However, after saturation point, any further increase in substrate concentration would only lead to a stable reaction kinetics.
Besides, the concentration of substrate, other factors like the pH, temperature also influence the break down of the substrate.