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

A substrate is a substance that converts to 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.

What is a 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 the peak when the enzyme is saturated by the substrate.

How does 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 gets modified into products.

This is given as a reaction below.

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

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 grams, eggs, and meat.

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

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

5. Ethyl alcohol is broken down by the enzyme alcohol dehydrogenase.

Other substrate examples with their role in the body

Sl.NoSubstrateThe enzyme (catalyst)Role in the body
1StarchAmylaseGlucose source
2ProteinPeptidaseAminoacid source
3LipidLipasefatty acids sorce
4Nucleic acids (DNA/RNA)NucleaseGenetic information
5ATPAdenylate cyclaseEnergy source
6GlucoseHexokinasegenerates ATP
7Lactoseβ-Galactosidasegenerates ATP
8CO2Carbonic anhydraseAcid-base homeostasis
9Estrogencytochrome P450Female reproductive hormone
10UreaUrease 
11Benzyl-penicillinPencillinase/ β-lactamaseAntibiotic kills bacteria
12AngiotensinogenReninRegulates blood pressure
13AlcoholAlcohol dehydrogenaseAs medicine and intoxicant

Neurotransmitters as substrates

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

Sl. NoSubstrateEnzyme name
1AcetylcholineAcetylcholinesterase and butyrylcholinesterase
2DopamineMonoamine oxidase (MAO) and
catechol-O-Methyltransferase (COMT)
3Nor-EpinephrineMAO and COMT
4EpinephrineMAO and COMT
5SerotoninMAO and COMT
6GABAGABA transaminase
7Glutamate glutamate dehydrogenase & aspartate aminotransferase
  • 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 all the active sites of the enzyme are occupied by the substrate, 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.

  1. Is lactose a substrate?

    Yes, lactose is a substrate for the enzyme lactase (beta-Galactosidase).
    It is mostly found in dairy products like milk, yogurt, curd, and cheese.

  2. What does “substrate level phosphorylation occurs” mean?

    It means the substrate is activated by the addition of a phosphate group to the chemical structure.

    This phosphorylation is done for further biochemical reactions.

    For example, glucose is phosphorylated to glucose-6-phosphate by hexokinase.

  3. Why do enzymes only work on their specific substrates

    Enzymes have a structural configuration in which only a specific substrate gets fixed by chemical bonds and undergo biochemical transformation.

References

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