What is a Substrate in Biology? (Role and Examples)

A substrate is a substance that converts into a product in the presence of enzymes.

Most substrates have only one specific enzyme to convert into a specific product.

But most enzymes can catalyze the reaction of two or more substrates.

So, a substrate undergoes a chemical transformation in the presence of a specific enzyme-mediated biochemical reaction.

It cannot undergo chemical change by other enzymes.

Substrate’s role in enzyme reaction?

• An enzyme catalyzes a reaction only in the presence of a substrate.
• An increase in substrate concentration can enhance the reaction rate.
• The rate of reaction reaches its peak when the substrate saturates the enzyme.

How does the substrate-enzyme interaction occur?

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 is modified into products.

This is given as a reaction below.

S + E <========>ES <===========> P + E.  {S= substrate ; E= enzyme; P= Product}

Examples of substrates

1. The Carbohydrates like sugar and starch act as substrates for enzymes like salivary amylase and maltase.

2. Amino acids, peptides, and proteins act as substrates for enzymes trypsin and chymotrypsin. These proteins are found in foods like grains, eggs, and meat.

3. Fatty acids act as substrates for lipase enzymes. Fats are obtained from food and by synthesis in the body.

4. Nucleic acids DNA and RNA are substrates for nuclease enzymes.

5. The enzyme alcohol dehydrogenase breaks down ethyl alcohol.

Other substrate examples and their role in the body

Sl.No	Substrate	The enzyme (catalyst)	Role in the body
1	Starch	Amylase	Glucose source
2	Protein	Peptidase	Aminoacid source
3	Lipid	Lipase	fatty acids sorce
4	Nucleic acids (DNA/RNA)	fatty acids source	Genetic information
5	ATP	Adenylate cyclase	Energy source
6	Glucose	Hexokinase	generates ATP
7	Lactose	β-Galactosidase	generates ATP
8	CO2	Carbonic anhydrase	Acid-base homeostasis
9	Estrogen	cytochrome P450	Female reproductive hormone
10	Urea	Urease	nitrogen waster
11	Benzyl-penicillin	Pencillinase/ β-lactamase	Antibiotic kills bacteria
12	Angiotensinogen	Renin	Regulates blood pressure
13	Alcohol	Alcohol dehydrogenase	As medicine and intoxicant

Neurotransmitters as substrates

Neurotransmitters are the chemical substances in the body that are involved in nerve conduction.

Sl. No	Substrate	Enzyme name	Role
1	Acetylcholine	Acetylcholinesterase and butyrylcholinesterase	Parasympathetic neurotransmitter
2	Dopamine	Monoamine oxidase (MAO) and catechol-O-Methyltransferase (COMT)
3	Nor-Epinephrine	MAO and COMT	Neurotransmitter in sympathetic system.
4	Epinephrine	MAO and COMT	Neurotransmitter in sympathetic system.
5	Serotonin	MAO and COMT	Regulates mood, cognition, reward, learning, memory, etc.
6	GABA	GABA transaminase	Inhibitory neurotransmitter
7	Glutamate	glutamate dehydrogenase & aspartate aminotransferase	Exitatory neurotransmitter.

• When substrate concentration is increased, the reaction rate is enhanced.

• This is because there are more substrate molecules ready to undergo biochemical reactions.

• However, this enhancement of reaction is limited.

• After the substrate occupies all the active sites of the enzyme, there will be no further increase in the rate of reaction.

• So, the remaining substrate molecules must wait until the previously bound molecules are broken down and removed.

• However, after the saturation point, any further increase in substrate concentration would only lead to stable reaction kinetics.

• Besides the concentration of substrate, other factors like pH and temperature also influence the breakdown of the substrate.

Frequently asked questions and answers.

References

• Alcohol Dehydrogenase