Metabolic intermediates are
compounds produced during the conversion of
substrates (starting molecules) into
final products in
biochemical reactions within
cells.
Although these intermediates are of relatively minor direct importance to cellular function, they can play important roles in the
allosteric regulation of
enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
s,
glycolysis
Glycolysis is the metabolic pathway that converts glucose () into pyruvic acid, pyruvate and, in most organisms, occurs in the liquid part of cells (the cytosol). The Thermodynamic free energy, free energy released in this process is used to form ...
, the
citric acid cycle
The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of chemical reaction, biochemical reactions that release the energy stored in nutrients through acetyl-Co ...
, and
amino acid synthesis.
Metabolic pathways
In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical ...
consist of a series of enzymatically catalyzed reactions where each step transforms a
substrate into a
product that serves as the
substrate for the next
reaction
Reaction may refer to a process or to a response to an action, event, or exposure.
Physics and chemistry
*Chemical reaction
*Nuclear reaction
*Reaction (physics), as defined by Newton's third law
* Chain reaction (disambiguation)
Biology and ...
. Metabolic intermediates are compounds that form during these steps, and they are neither the
starting substrate nor the
final product
In production, a final product or finished product is a product that is ready for sale,Wouters, Mark; Selto, Frank H.; Hilton, Ronald W.; Maher, Michael W. (2012): ''Cost Management: Strategies for Business Decisions'', International Edition, ...
of the pathway. These intermediates are crucial because they allow for regulation, energy storage, and extraction of
chemical energy
Chemical energy is the energy of chemical substances that is released when the substances undergo a chemical reaction and transform into other substances. Some examples of storage media of chemical energy include batteries, Schmidt-Rohr, K. (20 ...
in a controlled manner.
Types of Metabolic Intermediates
Metabolic intermediates can belong to different biochemical classes based on the type of
pathway they are involved in. Some examples include:
* Carbohydrate intermediates: In carbohydrate metabolism, intermediates such as
glucose-6-phosphate and
fructose-1,6-bisphosphate appear during
glycolysis
Glycolysis is the metabolic pathway that converts glucose () into pyruvic acid, pyruvate and, in most organisms, occurs in the liquid part of cells (the cytosol). The Thermodynamic free energy, free energy released in this process is used to form ...
and
gluconeogenesis
Gluconeogenesis (GNG) is a metabolic pathway that results in the biosynthesis of glucose from certain non-carbohydrate carbon substrates. It is a ubiquitous process, present in plants, animals, fungi, bacteria, and other microorganisms. In verte ...
.
* Amino acid intermediates: During
amino acid biosynthesis or
degradation, intermediates such as
2-oxoglutarate,
pyruvate
Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell.
Pyruvic ...
, or
oxaloacetate
Oxaloacetic acid (also known as oxalacetic acid or OAA) is a crystalline organic compound with the chemical formula HO2CC(O)CH2CO2H. Oxaloacetic acid, in the form of its conjugate base oxaloacetate, is a metabolic intermediate in many processes ...
are produced. These intermediates also link to the
citric acid cycle
The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of chemical reaction, biochemical reactions that release the energy stored in nutrients through acetyl-Co ...
.
* Lipid intermediates:
Fatty acid metabolism
Fatty acid metabolism consists of various metabolic processes involving or closely related to fatty acids, a family of molecules classified within the lipid macronutrient category. These processes can mainly be divided into (1) catabolic processe ...
involves intermediates like
acyl-CoA
Acyl-CoA is a group of coenzyme A, CoA-based coenzymes that metabolize carboxylic acids. Fatty acyl-CoA's are susceptible to beta oxidation, forming, ultimately, acetyl-CoA. The acetyl-CoA enters the citric acid cycle, eventually forming several e ...
derivatives during
β-oxidation or
fatty acid synthesis
In biochemistry, fatty acid synthesis is the creation of fatty acids from acetyl-CoA and NADPH through the action of enzymes. Two ''De novo synthesis, de novo'' fatty acid syntheses can be distinguished: cytosolic fatty acid synthesis (FAS/FASI) ...
.
* Nucleotide intermediates: The metabolism of
nucleotides
Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...
, the building blocks of
DNA
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
and
RNA
Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...
, includes intermediates like
inosine monophosphate (IMP), which is part of
purine biosynthesis.
Clinical significance
Some can be useful in measuring rates of metabolic processes (for example,
3,4-dihydroxyphenylacetic acid or
3-aminoisobutyrate).
Because they can represent unnatural points of entry into natural metabolic pathways, some (such as
AICA ribonucleotide
5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) is an intermediate in the generation of inosine monophosphate. AICAR is an analog of adenosine monophosphate (AMP) that is capable of stimulating AMP-dependent protein kinase (AMPK) activi ...
) are of interest to researchers in developing new therapies.
See also
*
Metabolism
Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
References
Metabolism
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