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Meta Description: Complete CSIR NET Life Science guide to group transfer reactions, ATP, PEP, 1,3-BPG, acetyl-CoA, SAM, PLP, transamination, kinases, phosphatases and thermodynamics.
1. Chapter 5 — Group Transfer
Group transfer is a fundamental biochemical process in which a specific functional group is transferred from one molecule to another. These reactions are essential for energy metabolism, biosynthesis, enzyme regulation, signal transduction, amino acid metabolism, carbohydrate metabolism, lipid metabolism, and nucleic acid metabolism.
A group-transfer reaction can be represented generally as:
Donor–Group + Acceptor → Donor + Acceptor–Group
For example:
ATP + Glucose → ADP + Glucose-6-phosphate
In this reaction, ATP donates a phosphoryl group to glucose. The enzyme responsible for the reaction is hexokinase.
Group transfer is particularly important in bioenergetics because many cellular reactions are coupled through the transfer of chemically activated groups. ATP-dependent phosphoryl transfer is one of the most important examples.
For CSIR NET Life Science, this topic should be understood through four major ideas:
- What group is transferred?
- Which molecule donates the group?
- Which molecule accepts the group?
- Why is the transfer thermodynamically and biologically useful?
1.1 Basic Concept of Group Transfer
A group-transfer reaction involves the movement of a functional group from a donor molecule to an acceptor molecule.
The general reaction is:
A–X + B → A + B–X
Where:
- A–X = donor molecule
- X = transferred group
- B = acceptor molecule
- B–X = modified acceptor
The enzyme catalyzing the reaction is generally a transferase.
Group transfer does not necessarily mean that the entire donor molecule is transferred. Only a specific chemical group moves from one molecule to another.
1.2 Why Group Transfer Is Important
Group transfer allows cells to modify molecules rapidly and selectively.
For example, phosphorylation of glucose converts:
Glucose → Glucose-6-phosphate
This modification:
- Adds negative charge to glucose.
- Helps retain glucose within the cell.
- Changes its chemical reactivity.
- Makes it suitable for subsequent metabolic reactions.
- Allows the cell to direct glucose toward different metabolic pathways.
Therefore, group transfer can simultaneously affect energy metabolism, molecular recognition, cellular localization, and regulation.
1.3 Group Transfer in Cellular Metabolism
Group-transfer reactions occur in almost every major metabolic pathway.
Examples include:
Glycolysis:
Glucose + ATP → Glucose-6-phosphate + ADP
1,3-BPG + ADP → 3-Phosphoglycerate + ATP
PEP + ADP → Pyruvate + ATP
Amino acid metabolism:
Alanine + α-ketoglutarate ⇌ Pyruvate + Glutamate
Citric acid cycle:
Oxaloacetate + Acetyl-CoA → Citrate + CoA-SH
Methylation:
SAM + Acceptor → Methylated acceptor + S-adenosylhomocysteine
These examples demonstrate that group transfer is not restricted to one pathway. It is a general strategy used by living systems.
2. Definition of Group Transfer
A group-transfer reaction is a biochemical reaction in which a functional group is transferred from a donor molecule to an acceptor molecule.
The general equation is:
A–X + B → A + B–X
The donor loses group X, while the acceptor gains group X.
Group-transfer reactions are generally catalyzed by enzymes belonging to the transferase class.
2.1 Donor Molecule
The donor molecule initially contains the functional group that will be transferred.
Important examples include:
| Donor | Group transferred |
|---|---|
| ATP | Phosphoryl group |
| Acetyl-CoA | Acetyl group |
| SAM | Methyl group |
| Amino acid | Amino group |
| UDP-glucose | Glycosyl group |
| Acyl-CoA | Acyl group |
The donor is frequently an activated compound, meaning that the group is present in a chemical form that allows efficient transfer.
2.2 Acceptor Molecule
The acceptor molecule receives the transferred group.
Examples include:
- Glucose receiving a phosphoryl group
- ADP receiving a phosphoryl group
- Oxaloacetate receiving an acetyl group
- α-Ketoglutarate receiving an amino group
- DNA receiving a methyl group
- Glycogen receiving a glycosyl group
The acceptor must contain a chemically suitable site for formation of the new bond.
2.3 Transferase Enzymes
Transferases are enzymes that catalyze the transfer of functional groups between molecules.
They belong to:
EC Class 2 — Transferases
Important transferases include:
- Kinases
- Aminotransferases
- Acyltransferases
- Glycosyltransferases
- Methyltransferases
The enzyme name frequently indicates the type of group being transferred.
For example:
Aminotransferase → amino-group transfer
Glycosyltransferase → glycosyl-group transfer
Methyltransferase → methyl-group transfer
2.4 General Mechanism of Group Transfer
The enzyme generally performs several functions:
- Binds the donor molecule.
- Binds the acceptor molecule.
- Positions the reacting groups correctly.
- Stabilizes the transition state.
- Facilitates bond breaking in the donor.
- Facilitates bond formation in the acceptor.
- Releases the products.
Thus, enzymes provide both specificity and catalytic efficiency.
3. Types of Transferred Groups
The major functional groups transferred in biological systems include:
- Phosphoryl group
- Acetyl group
- Methyl group
- Amino group
- Glycosyl group
- Acyl group
Each group has specific donors, acceptors, enzymes, and biological functions.
3.1 Phosphoryl-Group Transfer
A phosphoryl group is commonly represented as:
–PO₃²⁻
Phosphoryl transfer is one of the most important forms of group transfer in metabolism.
ATP is the major phosphoryl donor in many cellular reactions.
Example:
ATP + Glucose → ADP + Glucose-6-phosphate
Phosphorylation can:
- Activate metabolic intermediates.
- Change molecular charge.
- Alter protein activity.
- Change molecular conformation.
- Regulate signal-transduction pathways.
3.2 Acetyl-Group Transfer
An acetyl group is:
CH₃CO–
The major biological acetyl donor is:
Acetyl-CoA
Acetyl transfer is important in:
- Citric acid cycle
- Fatty acid metabolism
- Protein acetylation
- Histone modification
- Acetylcholine synthesis
- Cholesterol metabolism
3.3 Methyl-Group Transfer
A methyl group is:
–CH₃
The principal biological methyl donor is:
S-adenosylmethionine (SAM)
SAM transfers methyl groups to:
- DNA
- RNA
- Proteins
- Lipids
- Small metabolites
Methyl transfer is particularly important in epigenetic regulation.
3.4 Amino-Group Transfer
Amino-group transfer is central to nitrogen metabolism.
The general reaction is:
Amino acid₁ + α-keto acid₂ ⇌ α-keto acid₁ + Amino acid₂
The enzymes responsible are called:
Aminotransferases or transaminases
Most aminotransferases require:
Pyridoxal phosphate (PLP).
3.5 Glycosyl-Group Transfer
Glycosyl groups are transferred during carbohydrate metabolism and biosynthesis.
Important activated sugar donors include:
- UDP-glucose
- UDP-galactose
- GDP-mannose
- UDP-N-acetylglucosamine
Glycosyltransferases participate in:
- Glycogen synthesis
- Glycoprotein synthesis
- Glycolipid synthesis
- Cell-wall biosynthesis
- Carbohydrate modification
3.6 Acyl-Group Transfer
An acyl group has the general structure:
R–CO–
Important acyl donors include:
- Acetyl-CoA
- Fatty acyl-CoA
- Acyl phosphates
Acyl transfer is important in:
- Fatty acid metabolism
- Lipid biosynthesis
- Citric acid cycle
- Protein modification
4. Phosphoryl-Group Transfer
Phosphoryl-group transfer is a central concept in cellular bioenergetics.
A phosphoryl group can be transferred from one compound to another when the overall reaction is thermodynamically favorable under the relevant cellular conditions.
The general reaction is:
Phosphoryl donor + Acceptor → Dephosphorylated donor + Phosphorylated acceptor
The tendency of a compound to donate its phosphoryl group is described by its phosphoryl-transfer potential.
4.1 ATP as a Phosphoryl Donor
ATP stands for:
Adenosine triphosphate
ATP consists of:
- Adenine
- Ribose
- Three phosphate groups
The phosphate groups are designated:
- α-phosphate
- β-phosphate
- γ-phosphate
The terminal γ-phosphate is frequently transferred during kinase reactions.
4.2 ATP-Dependent Phosphoryl Transfer
A general reaction is:
ATP + R–OH → ADP + R–OPO₃²⁻
For example:
Glucose + ATP → Glucose-6-phosphate + ADP
This reaction is catalyzed by hexokinase.
The phosphoryl group changes the chemical properties of glucose and allows it to participate in subsequent reactions.
4.3 Biological Effects of Phosphorylation
Phosphorylation can:
- Increase negative charge.
- Change molecular conformation.
- Alter enzyme activity.
- Create recognition sites.
- Change protein-protein interactions.
- Alter cellular localization.
- Activate metabolic pathways.
- Inhibit metabolic pathways.
- Regulate signal transduction.
Thus, phosphorylation is both a metabolic and regulatory modification.
4.4 Phosphorylation of Proteins
Protein phosphorylation is one of the most important reversible covalent modifications.
The common target residues are:
- Serine
- Threonine
- Tyrosine
A simplified reaction is:
Protein–OH + ATP → Protein–OPO₃²⁻ + ADP
Protein phosphorylation is involved in:
- Cell signaling
- Cell-cycle regulation
- Metabolic control
- Gene regulation
- Cytoskeletal regulation
5. ATP-Dependent Phosphoryl Transfer
ATP-dependent phosphoryl transfer is one of the most common group-transfer reactions in living cells.
The general reaction is:
ATP + Substrate → ADP + Phosphorylated substrate
The enzyme is generally a kinase.
5.1 Role of Mg²⁺
ATP commonly exists in association with magnesium ions.
Many kinase reactions effectively use MgATP as the substrate.
Mg²⁺ helps:
- Shield negative charges on ATP.
- Stabilize the phosphate groups.
- Position ATP correctly.
- Facilitate interaction between ATP and the acceptor.
- Support catalytic phosphoryl transfer.
This is an important mechanistic concept for CSIR NET.
5.2 Examples of ATP-Dependent Phosphorylation
Hexokinase
Glucose + ATP → Glucose-6-phosphate + ADP
Phosphofructokinase-1
Fructose-6-phosphate + ATP → Fructose-1,6-bisphosphate + ADP
Protein Kinase
Protein–OH + ATP → Protein–OPO₃²⁻ + ADP
These reactions demonstrate that ATP can phosphorylate both small metabolites and proteins.
5.3 ATP as an Energy-Coupling Molecule
ATP does not simply “contain energy” that is released whenever ATP is present.
Instead, ATP participates in specific chemical reactions.
ATP hydrolysis or phosphoryl transfer can be mechanistically coupled to another reaction.
This distinction is important for understanding bioenergetics correctly.
6. Phosphoryl-Transfer Potential
Phosphoryl-transfer potential describes the tendency of a phosphorylated compound to transfer its phosphoryl group to another molecule.
It is commonly related to the free-energy change of hydrolysis.
The general hydrolysis reaction is:
Phosphorylated compound + H₂O → Dephosphorylated compound + Pi
A compound with a more negative standard free energy of hydrolysis generally has a greater phosphoryl-transfer potential.
6.1 Why Hydrolysis Is Used to Compare Transfer Potential
Direct comparison of transfer reactions can be complicated because the acceptor varies.
Therefore, biochemical comparisons often use the standard free-energy change of hydrolysis.
For example:
PEP + H₂O → Pyruvate + Pi
can be compared thermodynamically with:
ATP + H₂O → ADP + Pi
If PEP hydrolysis has a more negative ΔG°′ than ATP hydrolysis, PEP has a greater phosphoryl-transfer potential.
6.2 High-Phosphoryl-Transfer-Potential Compounds
Important compounds include:
- PEP
- 1,3-BPG
- Phosphocreatine
- ATP
A major CSIR NET concept is:
ATP is not the highest phosphoryl-transfer-potential compound in metabolism.
PEP and 1,3-BPG have greater phosphoryl-transfer potential than ATP.
6.3 Meaning of a “High-Energy” Phosphate Compound
The term high-energy phosphate compound refers to a compound whose hydrolysis has a strongly negative free-energy change.
It does not mean that the phosphate bond itself simply contains a fixed amount of stored energy.
The favorable reaction can arise from:
- Resonance stabilization of products
- Reduction of electrostatic repulsion
- Better solvation
- Ionization effects
- Product stabilization
- Entropic contributions
Therefore, phosphoryl-transfer potential is a more precise concept.
7. ATP vs ADP
ATP and ADP form one of the most important energy-transfer systems in cells.
ATP = Adenosine triphosphate
ADP = Adenosine diphosphate
ATP contains three phosphate groups, while ADP contains two.
7.1 ATP Hydrolysis
The simplified reaction is:
ATP + H₂O → ADP + Pi
ATP hydrolysis has a negative free-energy change under standard biochemical conditions.
However, actual cellular ΔG depends on:
- ATP concentration
- ADP concentration
- Pi concentration
- pH
- Temperature
- Ionic conditions
Therefore:
ΔG ≠ necessarily ΔG°′
under actual cellular conditions.
7.2 ATP as the Energy Currency
ATP is commonly called the energy currency of the cell because it provides a convenient connection between energy-producing and energy-consuming reactions.
A simplified representation is:
Catabolism → ATP → Cellular work
Cellular work includes:
- Biosynthesis
- Active transport
- Mechanical work
- Signal transduction
- Macromolecular assembly
7.3 ATP Is Not a Long-Term Energy Store
ATP is primarily a rapid energy-transfer intermediate.
Long-term energy storage is mainly achieved through:
- Triacylglycerols
- Glycogen
ATP is continuously regenerated and consumed.
Thus, ATP is better viewed as a rapidly circulating energy currency than as a long-term storage molecule.
7.4 ATP/ADP Ratio
The ATP/ADP ratio provides information about the energetic state of a cell.
A high ATP/ADP ratio generally indicates a relatively energy-rich state, whereas a lower ratio indicates increased energy demand.
Cells use this information to regulate metabolic pathways.
8. Phosphoenolpyruvate (PEP)
Phosphoenolpyruvate (PEP) is a high-energy phosphorylated intermediate of glycolysis.
The reaction catalyzed by pyruvate kinase is:
PEP + ADP → Pyruvate + ATP
This reaction represents substrate-level phosphorylation.
8.1 Why PEP Has High Phosphoryl-Transfer Potential
PEP has a very high phosphoryl-transfer potential.
When PEP loses its phosphoryl group, pyruvate is initially formed in an enol form.
Pyruvate then undergoes:
Enol form → Keto form
The keto form is more stable.
This additional stabilization strongly favors the overall reaction.
8.2 PEP and ATP Formation
Because PEP has greater phosphoryl-transfer potential than ATP, it can phosphorylate ADP:
PEP + ADP → Pyruvate + ATP
This demonstrates that a high-transfer-potential phosphoryl donor can drive ATP formation.
8.3 CSIR NET Importance
A common conceptual question is:
Why can PEP generate ATP from ADP?
Because PEP has a higher phosphoryl-transfer potential than ATP, and formation of stable keto pyruvate strongly favors the reaction.
9. 1,3-Bisphosphoglycerate (1,3-BPG)
1,3-Bisphosphoglycerate (1,3-BPG) is another high-energy intermediate of glycolysis.
It contains an acyl phosphate bond, which contributes to its high phosphoryl-transfer potential.
The reaction is:
1,3-BPG + ADP → 3-Phosphoglycerate + ATP
Enzyme:
Phosphoglycerate kinase
9.1 Formation of 1,3-BPG
During glycolysis:
Glyceraldehyde-3-phosphate + Pi + NAD⁺ → 1,3-BPG + NADH + H⁺
Enzyme:
Glyceraldehyde-3-phosphate dehydrogenase
This reaction couples oxidation of glyceraldehyde-3-phosphate with formation of a high-energy phosphorylated intermediate.
9.2 1,3-BPG and ATP Formation
The next reaction transfers the phosphoryl group to ADP:
1,3-BPG + ADP → 3-PG + ATP
This is substrate-level phosphorylation.
9.3 Important Metabolic Principle
This part of glycolysis illustrates:
Oxidation → Energy conservation → High-energy intermediate → ATP synthesis
It is an excellent example of coupling between redox chemistry and phosphoryl transfer.
10. Creatine Phosphate
Creatine phosphate, also called phosphocreatine, is an important phosphoryl-group reservoir in vertebrate tissues.
The reaction is:
Phosphocreatine + ADP ⇌ Creatine + ATP
Enzyme:
Creatine kinase
10.1 Function of Phosphocreatine
Phosphocreatine provides a rapidly available source of phosphoryl groups for ATP regeneration.
During sudden energy demand:
Phosphocreatine + ADP → Creatine + ATP
This helps maintain ATP concentration.
10.2 Phosphocreatine as an Energy Buffer
The phosphocreatine system is particularly important in:
- Skeletal muscle
- Cardiac muscle
- Brain
It acts as a short-term buffer between ATP production and ATP consumption.
10.3 Creatine Kinase Reaction
Creatine kinase catalyzes a reversible reaction:
Phosphocreatine + ADP ⇌ Creatine + ATP
During high energy demand, the reaction tends toward ATP formation.
During recovery, ATP can be used to regenerate phosphocreatine.
11. Acetyl-CoA and Acetyl-Group Transfer
Acetyl-CoA is one of the most important activated group carriers in metabolism.
Its simplified structure is:
CH₃–CO–S–CoA
The acetyl group is attached to coenzyme A through a thioester bond.
11.1 Acetyl-CoA as an Acetyl Donor
Acetyl-CoA can transfer its acetyl group to suitable acceptors.
The activated thioester makes acetyl-CoA an effective acetyl-group donor.
11.2 Importance of the Thioester Bond
Thioesters are relatively reactive acyl compounds.
Hydrolysis of the thioester is favorable because the products are more stabilized than the reactant.
This makes acetyl-CoA useful in biosynthetic and catabolic pathways.
11.3 Acetyl-CoA in the Citric Acid Cycle
The first reaction of the citric acid cycle is:
Oxaloacetate + Acetyl-CoA + H₂O → Citrate + CoA-SH
Enzyme:
Citrate synthase
The acetyl group becomes incorporated into citrate.
11.4 Other Functions of Acetyl-CoA
Acetyl-CoA participates in:
- Citric acid cycle
- Fatty acid synthesis
- Fatty acid oxidation
- Ketone-body metabolism
- Cholesterol synthesis
- Histone acetylation
- Protein acetylation
- Acetylcholine synthesis
Thus, acetyl-CoA acts as both a metabolic intermediate and an activated acetyl-group donor.
12. S-Adenosylmethionine (SAM)
S-adenosylmethionine (SAM) is the major biological methyl-group donor.
SAM is synthesized from methionine and ATP.
A simplified reaction is:
Methionine + ATP → SAM
SAM contains a positively charged sulfonium center, making its methyl group highly transferable.
12.1 Methyl-Group Transfer by SAM
The general reaction is:
SAM + Acceptor → S-adenosylhomocysteine + Methylated acceptor
The acceptor may be:
- DNA
- RNA
- Protein
- Lipid
- Small metabolite
12.2 SAM and DNA Methylation
SAM provides methyl groups for DNA methylation.
DNA methylation can influence:
- Gene expression
- Chromatin organization
- Development
- Cellular differentiation
- Genome stability
Thus, metabolism can directly influence gene regulation through SAM availability.
12.3 SAM and RNA Methylation
SAM-dependent RNA methylation can influence:
- RNA stability
- RNA processing
- Translation
- RNA-protein interactions
12.4 SAM in Metabolism
SAM-dependent methylation reactions are also involved in the synthesis and modification of many metabolites.
For CSIR NET, the most important association is:
SAM → Methyl-group donor
13. PLP-Dependent Amino-Group Transfer
Pyridoxal phosphate (PLP) is the active coenzyme form of vitamin B₆.
PLP is required by many enzymes involved in amino acid metabolism.
Important PLP-dependent reactions include:
- Transamination
- Decarboxylation
- Racemization
- Elimination reactions
13.1 Chemical Role of PLP
PLP contains a reactive aldehyde group.
It can form a Schiff-base linkage with amino groups.
This allows PLP to participate directly in amino acid transformations.
13.2 PLP as an Electron Sink
PLP acts as an electron sink.
During an amino acid reaction, electron density can be delocalized into the PLP system.
This stabilizes reaction intermediates.
This is the major mechanistic reason PLP is so useful in amino acid chemistry.
13.3 Importance of PLP
PLP-dependent enzymes participate in:
- Amino acid degradation
- Amino acid biosynthesis
- Neurotransmitter synthesis
- Nitrogen metabolism
- Amino acid interconversion
14. Transamination
Transamination is the transfer of an amino group from an amino acid to an α-keto acid.
The general reaction is:
Amino acid₁ + α-keto acid₂ ⇌ α-keto acid₁ + Amino acid₂
The enzymes are:
Aminotransferases or transaminases
Most require PLP.
14.1 Alanine Transamination
A classic reaction is:
Alanine + α-ketoglutarate ⇌ Pyruvate + Glutamate
Enzyme:
Alanine aminotransferase (ALT)
The amino group from alanine is transferred to α-ketoglutarate.
The carbon skeleton of alanine becomes pyruvate.
14.2 Aspartate Transamination
Another important reaction is:
Aspartate + α-ketoglutarate ⇌ Oxaloacetate + Glutamate
Enzyme:
Aspartate aminotransferase (AST)
This connects amino acid metabolism with the citric acid cycle.
14.3 Glutamate as a Central Nitrogen Carrier
Many amino acids transfer their amino groups to α-ketoglutarate.
This produces:
Glutamate
Glutamate therefore acts as an important collector of amino groups.
A simplified sequence is:
Amino acids → Transamination → Glutamate → Oxidative deamination → Ammonia
14.4 Transamination and Nitrogen Metabolism
Transamination allows nitrogen to be redistributed among carbon skeletons without requiring immediate release of free ammonia.
This is important for both amino acid synthesis and degradation.
15. Kinases
Kinases are enzymes that catalyze phosphoryl-group transfer.
A common reaction is:
ATP + Substrate → ADP + Phosphorylated substrate
Kinases are essential in metabolism and cellular signaling.
15.1 Kinases in Glycolysis
Important glycolytic kinases include:
- Hexokinase
- Phosphofructokinase-1
- Phosphoglycerate kinase
- Pyruvate kinase
These enzymes participate in both ATP consumption and ATP generation.
15.2 Hexokinase
Reaction:
Glucose + ATP → Glucose-6-phosphate + ADP
Importance:
- Traps glucose within the cell.
- Activates glucose.
- Initiates glycolytic metabolism.
15.3 Phosphofructokinase-1
Reaction:
Fructose-6-phosphate + ATP → Fructose-1,6-bisphosphate + ADP
PFK-1 is a major regulatory enzyme of glycolysis.
15.4 Phosphoglycerate Kinase
Reaction:
1,3-BPG + ADP → 3-Phosphoglycerate + ATP
This produces ATP by substrate-level phosphorylation.
15.5 Pyruvate Kinase
Reaction:
PEP + ADP → Pyruvate + ATP
This is another substrate-level phosphorylation reaction.
15.6 Protein Kinases
Protein kinases transfer phosphate groups from ATP to proteins.
Common target residues include:
- Serine
- Threonine
- Tyrosine
Protein phosphorylation can regulate:
- Enzyme activity
- Protein conformation
- Protein stability
- Protein localization
- Protein-protein interactions
- Signal transduction
16. Phosphatases
Phosphatases catalyze removal of phosphate groups from phosphorylated molecules.
A simplified reaction is:
Phosphorylated substrate + H₂O → Dephosphorylated substrate + Pi
16.1 Biological Roles of Phosphatases
Phosphatases are important in:
- Metabolic regulation
- Signal termination
- Cell-cycle regulation
- Protein regulation
- Cellular homeostasis
16.2 Kinase vs Phosphatase
Kinase:
Transfers a phosphoryl group to a substrate.
Phosphatase:
Removes a phosphate group from a substrate.
They are generally distinct enzymes and are not simply the forward and reverse forms of the same enzyme.
16.3 Phosphorylation-Dephosphorylation Cycle
A protein can exist as:
Protein ⇌ Phosphorylated protein
Kinases promote phosphorylation.
Phosphatases promote dephosphorylation.
This provides a rapid and reversible mechanism for cellular regulation.
17. Acyl Transfer
Acyl transfer involves movement of an acyl group:
R–CO–
from one molecule to another.
The general reaction is:
Acyl donor + Acceptor → Donor without acyl group + Acylated acceptor
17.1 Acyl Donors
Important activated acyl donors include:
- Acetyl-CoA
- Fatty acyl-CoA
- Acyl phosphates
17.2 Acyl-CoA in Lipid Metabolism
Acyl-CoA compounds are essential for:
- β-Oxidation
- Fatty acid synthesis
- Triacylglycerol synthesis
- Phospholipid synthesis
17.3 Biological Importance of Acyl Transfer
Acyl transfer allows cells to construct and modify lipids efficiently.
Activated acyl groups can be transferred to glycerol derivatives and other acceptors during lipid biosynthesis.
18. Glycosyl-Group Transfer
Glycosyl transfer is important in carbohydrate metabolism and glycoconjugate biosynthesis.
Cells frequently use activated sugar donors rather than free sugars.
Important donors include:
- UDP-glucose
- UDP-galactose
- GDP-mannose
18.1 Glycogen Synthesis
During glycogen synthesis, glucose residues are transferred from UDP-glucose to the growing glycogen chain.
A simplified reaction is:
UDP-glucose + Glycogenₙ → UDP + Glycogenₙ₊₁
The enzyme responsible for chain elongation is:
Glycogen synthase
18.2 Glycosyltransferases
Glycosyltransferases transfer glycosyl groups to acceptor molecules.
They participate in:
- Glycoprotein synthesis
- Glycolipid synthesis
- Glycogen synthesis
- Cell-wall biosynthesis
- Extracellular matrix modification
19. Biological Importance of Group Transfer
Group-transfer reactions have extensive biological importance.
19.1 Energy Transfer
Phosphoryl transfer allows ATP to connect energy-producing and energy-consuming reactions.
19.2 Metabolic Activation
Phosphorylation can make molecules more reactive or prepare them for subsequent reactions.
19.3 Enzyme Regulation
Protein phosphorylation and dephosphorylation rapidly regulate enzyme activity.
19.4 Signal Transduction
Kinases and phosphatases are major components of cellular signaling.
19.5 Biosynthesis
Group transfer is essential for:
- DNA synthesis
- RNA synthesis
- Protein modification
- Glycogen synthesis
- Lipid synthesis
- Carbohydrate biosynthesis
19.6 Nitrogen Metabolism
Amino-group transfer connects amino acid metabolism with central carbon metabolism.
19.7 Gene Regulation
Methyl and acetyl group transfer can influence chromatin structure and gene expression.
20. Group-Transfer Reactions in Glycolysis
Glycolysis contains several important phosphoryl-transfer reactions.
20.1 Glucose Phosphorylation
Glucose + ATP → Glucose-6-phosphate + ADP
Enzyme:
Hexokinase
Functions:
- Traps glucose within the cell.
- Activates glucose.
- Initiates glycolysis.
20.2 Fructose-6-Phosphate Phosphorylation
Fructose-6-phosphate + ATP → Fructose-1,6-bisphosphate + ADP
Enzyme:
Phosphofructokinase-1
This is a major regulatory step of glycolysis.
20.3 ATP Formation From 1,3-BPG
1,3-BPG + ADP → 3-Phosphoglycerate + ATP
Enzyme:
Phosphoglycerate kinase
This is substrate-level phosphorylation.
20.4 ATP Formation From PEP
PEP + ADP → Pyruvate + ATP
Enzyme:
Pyruvate kinase
This is the second substrate-level phosphorylation step of glycolysis.
21. Group Transfer in the Citric Acid Cycle
Acetyl-CoA enters the citric acid cycle through acetyl-group transfer.
The reaction is:
Oxaloacetate + Acetyl-CoA + H₂O → Citrate + CoA-SH
Enzyme:
Citrate synthase
The acetyl group contributes two carbon atoms to citrate.
21.1 Acetyl-CoA as a Metabolic Hub
Acetyl-CoA connects:
- Carbohydrate metabolism
- Fatty acid metabolism
- Amino acid metabolism
- Citric acid cycle
- Ketone-body metabolism
- Cholesterol biosynthesis
Therefore, acetyl-CoA is one of the most important metabolic branch points.
22. Group Transfer in Amino Acid Metabolism
Amino-group transfer is a major feature of amino acid metabolism.
The general reaction is:
Amino acid + α-keto acid ⇌ α-keto acid + Amino acid
22.1 Connection With Central Carbon Metabolism
Transamination allows amino acids to exchange amino groups with central metabolic intermediates.
For example:
Alanine ⇌ Pyruvate
through transfer of the amino group between alanine and α-ketoglutarate/glutamate.
This connects amino acid metabolism with glycolysis.
22.2 Glutamate as a Nitrogen Collector
Many transamination reactions transfer amino groups to α-ketoglutarate.
Therefore:
α-Ketoglutarate + amino group → Glutamate
Glutamate can then participate in oxidative deamination and other nitrogen-handling reactions.
23. Group Transfer in Signal Transduction
Protein phosphorylation is one of the most important reversible regulatory mechanisms in cells.
A simplified pathway is:
Signal → Receptor → Protein kinase → Protein phosphorylation → Cellular response
Phosphatases can remove the phosphate group.
23.1 Phosphorylation as a Molecular Switch
A protein can exist in:
Unphosphorylated state ⇌ Phosphorylated state
The two forms may have different:
- Activities
- Conformations
- Binding partners
- Cellular locations
This allows cells to respond rapidly to extracellular and intracellular signals.
23.2 Kinase Cascades
Many signaling pathways involve sequential phosphorylation:
Kinase 1 → Kinase 2 → Kinase 3 → Target protein
Such cascades can amplify signals and coordinate cellular responses.
24. Energy Conservation Through Group Transfer
Group transfer is closely connected with energy conservation.
During catabolic reactions, free energy can be captured in:
- ATP
- NADH
- FADH₂
- High-energy metabolic intermediates
These molecules can then support energy-demanding cellular processes.
24.1 High-Energy Intermediate Concept
A high-energy intermediate is a compound whose hydrolysis or group-transfer reaction has a strongly favorable free-energy change.
Important examples include:
- PEP
- 1,3-BPG
- Phosphocreatine
- ATP
24.2 Energy Flow
A simplified representation is:
Nutrients
↓
Oxidative reactions
↓
Energy capture
↓
ATP / High-energy intermediates
↓
Group transfer
↓
Cellular work
This illustrates the connection between metabolism and bioenergetics.
25. Thermodynamic Basis of Group Transfer
Thermodynamics determines whether a group-transfer reaction is favorable under particular conditions.
The fundamental relationship is:
ΔG = ΔG°′ + RT ln Q
Where:
- ΔG = actual Gibbs free-energy change
- ΔG°′ = standard transformed Gibbs free-energy change
- R = gas constant
- T = absolute temperature
- Q = reaction quotient
25.1 When ΔG Is Negative
If:
ΔG < 0
the forward reaction is thermodynamically favorable under the specified conditions.
25.2 When ΔG Is Positive
If:
ΔG > 0
the forward reaction is thermodynamically unfavorable under the specified conditions.
25.3 When ΔG Equals Zero
At equilibrium:
ΔG = 0
There is no net thermodynamic driving force in either direction.
25.4 ΔG vs ΔG°′
ΔG°′ describes the standard transformed free-energy change.
ΔG describes the actual free-energy change under the conditions being considered.
Therefore, the two values do not have to be equal.
The cellular reaction direction depends on:
ΔG = ΔG°′ + RT ln Q
26. Coupling of Group-Transfer Reactions
Many biochemical reactions are unfavorable when considered individually.
Cells solve this problem by coupling unfavorable reactions with favorable reactions.
If:
Reaction 1: ΔG₁ > 0
and:
Reaction 2: ΔG₂ < 0
then:
ΔGtotal = ΔG₁ + ΔG₂
If the total is negative, the coupled reaction becomes favorable.
26.1 Example of Coupling
Suppose:
Reaction A = +20 kJ/mol
Reaction B = −30 kJ/mol
Then:
ΔGtotal = +20 − 30
ΔGtotal = −10 kJ/mol
Therefore, the combined process is favorable.
26.2 ATP-Dependent Coupling
ATP hydrolysis is favorable:
ATP + H₂O → ADP + Pi
An unfavorable reaction can be coupled to ATP hydrolysis.
The important point is that ATP hydrolysis must be mechanistically coupled to the reaction being driven.
ATP does not simply release energy into the surrounding solution and automatically make every nearby reaction favorable.
27. Substrate-Level Phosphorylation
Substrate-level phosphorylation is the direct synthesis of ATP by transfer of a phosphoryl group from a high-energy metabolic intermediate to ADP.
Important examples are:
1,3-BPG + ADP → 3-PG + ATP
PEP + ADP → Pyruvate + ATP
27.1 Substrate-Level vs Oxidative Phosphorylation
| Feature | Substrate-Level Phosphorylation | Oxidative Phosphorylation |
|---|---|---|
| Immediate energy source | High-energy metabolic intermediate | Proton-motive force |
| Direct phosphoryl donor | Metabolic intermediate | Pi |
| Electron transport chain | Not required | Required |
| Proton gradient | Not required | Required |
| Example | PEP → ATP | ETC-driven ATP synthesis |
This distinction is highly important for CSIR NET.
28. Group Transfer and Redox Reactions
Group-transfer reactions can be closely linked with oxidation-reduction reactions.
A classic example is the formation of 1,3-BPG:
Glyceraldehyde-3-phosphate + Pi + NAD⁺ → 1,3-BPG + NADH + H⁺
Here:
- Glyceraldehyde-3-phosphate is oxidized.
- NAD⁺ is reduced.
- A high-energy phosphorylated intermediate is produced.
The next reaction transfers the phosphoryl group to ADP:
1,3-BPG + ADP → 3-PG + ATP
Therefore:
Oxidation → High-energy intermediate → Group transfer → ATP formation
This is an important example of metabolic coupling.
29. Group Transfer and Metabolic Regulation
Group transfer provides a rapid mechanism for regulating metabolic pathways.
Phosphorylation can alter enzyme activity without requiring synthesis of a new protein.
29.1 Reversible Covalent Modification
Protein phosphorylation is a reversible covalent modification:
Protein ⇌ Phosphorylated protein
The phosphorylated and unphosphorylated forms can have different activities.
29.2 Advantages of Phosphorylation
Phosphorylation provides:
- Rapid regulation
- Reversibility
- Signal amplification
- Pathway integration
- Control of enzyme activity
29.3 Kinase-Phosphatase Balance
Cellular responses often depend on the balance between kinase and phosphatase activities.
Kinase activity ↑ → Phosphorylation ↑
Phosphatase activity ↑ → Dephosphorylation ↑
This balance is important for maintaining cellular homeostasis.
30. Group Transfer and Compartmentalization
Group transfer can influence where metabolites remain within a cell.
For example:
Glucose → Glucose-6-phosphate
Glucose-6-phosphate carries substantial negative charge and cannot freely diffuse across the lipid bilayer.
Therefore, phosphorylation helps retain glucose-derived carbon inside the cell.
This demonstrates that group transfer can affect:
- Chemical reactivity
- Charge
- Solubility
- Cellular localization
- Metabolic fate
31. Group Transfer in Nucleic Acid Metabolism
Phosphoryl-group chemistry is fundamental to DNA and RNA synthesis.
31.1 DNA Synthesis
DNA polymerases use deoxyribonucleoside triphosphates.
The incoming nucleotide contains high-energy phosphoanhydride bonds.
Formation of the phosphodiester bond is coupled to release of pyrophosphate.
31.2 RNA Synthesis
RNA polymerases use ribonucleoside triphosphates.
The high-energy phosphate chemistry of nucleoside triphosphates supports phosphodiester-bond formation.
Thus, phosphoryl chemistry is fundamental to nucleic acid biosynthesis.
32. Group Transfer in Macromolecule Biosynthesis
Group transfer is essential for constructing biological macromolecules.
Examples include:
- Glycosyl transfer during polysaccharide synthesis
- Phosphoryl transfer during nucleotide metabolism
- Acyl transfer during lipid synthesis
- Aminoacyl transfer during protein synthesis
- Methyl transfer during nucleic acid modification
32.1 Activated Group Donors
Cells commonly use activated group donors.
Important examples are:
ATP → phosphoryl donor
Acetyl-CoA → acetyl donor
SAM → methyl donor
UDP-glucose → glycosyl donor
Aminoacyl-tRNA → aminoacyl donor
This is a general strategy used throughout biochemistry.
33. Biological Importance of Activated Group Donors
Activated group donors are important because the transferred group is held in a chemical environment that makes transfer favorable or kinetically accessible.
For example:
- ATP contains phosphoanhydride bonds.
- Acetyl-CoA contains a reactive thioester.
- SAM contains an activated methyl group.
- UDP-glucose contains an activated glycosyl group.
The cell therefore uses chemical activation to make difficult reactions possible.
34. Important Donor–Group Associations
| Donor | Group transferred | Major biological function |
|---|---|---|
| ATP | Phosphoryl | Energy coupling and regulation |
| PEP | Phosphoryl | ATP formation |
| 1,3-BPG | Phosphoryl | ATP formation |
| Phosphocreatine | Phosphoryl | ATP buffering |
| Acetyl-CoA | Acetyl | Central metabolism |
| SAM | Methyl | Biological methylation |
| Amino acid | Amino | Nitrogen metabolism |
| UDP-glucose | Glycosyl | Carbohydrate biosynthesis |
| Acyl-CoA | Acyl | Lipid metabolism |
35. Important Enzyme–Reaction Associations
35.1 Hexokinase
Glucose + ATP → Glucose-6-phosphate + ADP
35.2 Phosphofructokinase-1
Fructose-6-phosphate + ATP → Fructose-1,6-bisphosphate + ADP
35.3 Phosphoglycerate Kinase
1,3-BPG + ADP → 3-Phosphoglycerate + ATP
35.4 Pyruvate Kinase
PEP + ADP → Pyruvate + ATP
35.5 Creatine Kinase
Phosphocreatine + ADP ⇌ Creatine + ATP
35.6 Aminotransferase
Amino acid + α-keto acid ⇌ α-keto acid + Amino acid
35.7 Citrate Synthase
Oxaloacetate + Acetyl-CoA → Citrate + CoA-SH
35.8 Protein Kinase
Protein–OH + ATP → Protein–OPO₃²⁻ + ADP
35.9 Phosphatase
Protein-P + H₂O → Protein + Pi
36. Group Transfer vs Hydrolysis
Group transfer and hydrolysis are different chemical processes.
36.1 Group Transfer
General reaction:
A–X + B → A + B–X
The group X is transferred to another molecule.
36.2 Hydrolysis
General reaction:
A–X + H₂O → A–OH + X
Water participates directly in bond cleavage.
36.3 ATP Example
ATP can undergo hydrolysis:
ATP + H₂O → ADP + Pi
ATP can also participate in phosphoryl transfer:
ATP + Substrate → ADP + Phosphorylated substrate
These are chemically different reactions.
37. Group Transfer vs Oxidation-Reduction
Group transfer should be distinguished from oxidation-reduction reactions.
37.1 Group Transfer
A functional group moves from one molecule to another.
Example:
ATP → Phosphoryl transfer
37.2 Oxidation-Reduction
Electrons or reducing equivalents are transferred.
Example:
NAD⁺ + 2e⁻ + H⁺ → NADH
37.3 Integration in Metabolism
Metabolic pathways often combine both processes.
For example:
Glyceraldehyde-3-phosphate oxidation
↓
1,3-BPG formation
↓
Phosphoryl transfer
↓
ATP formation
This illustrates the integration of redox chemistry and group transfer.
38. Enzymes and Thermodynamics
One of the most important CSIR NET concepts is the distinction between kinetics and thermodynamics.
38.1 What Enzymes Change
Enzymes lower the activation energy:
ΔG‡ ↓
This increases the reaction rate.
38.2 What Enzymes Do Not Change
Enzymes do not change:
- Overall ΔG
- ΔG°′
- Equilibrium constant
- Thermodynamic equilibrium
Therefore:
Enzyme → changes reaction rate
but:
Enzyme → does not change overall reaction thermodynamics
38.3 Importance for Group Transfer
If a group-transfer reaction is thermodynamically unfavorable, simply adding an enzyme does not make it favorable.
The reaction must instead be driven by:
- Coupling
- Changes in substrate/product concentrations
- Another favorable reaction
- Appropriate cellular conditions
39. High-Yield CSIR NET Concepts
39.1 ATP Is Not the Highest Phosphoryl-Transfer-Potential Compound
The statement:
“ATP has the highest phosphoryl-transfer potential.”
is incorrect.
PEP and 1,3-BPG have greater phosphoryl-transfer potential than ATP.
39.2 ATP Is an Energy-Coupling Molecule
ATP connects:
Energy-releasing reactions
with:
Energy-consuming reactions
It is continuously regenerated and consumed.
39.3 SAM Is a Methyl Donor
Remember:
SAM → Methyl-group donor
39.4 Acetyl-CoA Is an Acetyl Donor
Remember:
Acetyl-CoA → Acetyl-group donor
39.5 PLP Is Associated With Amino Acid Chemistry
Remember:
PLP → Transamination and other amino acid reactions
39.6 Kinases and Phosphatases Are Different
Remember:
Kinase → Phosphoryl transfer
Phosphatase → Phosphate removal
39.7 ΔG Determines Thermodynamic Favorability
Remember:
ΔG < 0 → Favorable
ΔG > 0 → Unfavorable
ΔG = 0 → Equilibrium
40. CSIR NET Comparisons
40.1 ATP vs PEP
ATP: Major cellular energy-coupling molecule.
PEP: Has higher phosphoryl-transfer potential and can phosphorylate ADP to form ATP.
40.2 ATP vs Phosphocreatine
ATP: Immediate energy-transfer molecule.
Phosphocreatine: Rapid phosphoryl reservoir used for ATP regeneration.
40.3 Acetyl-CoA vs SAM
Acetyl-CoA: Acetyl-group donor.
SAM: Methyl-group donor.
40.4 Kinase vs Phosphatase
Kinase: Transfers phosphoryl groups.
Phosphatase: Removes phosphate groups.
40.5 PLP vs NAD⁺
PLP: Important in amino acid reactions.
NAD⁺: Major electron acceptor in oxidation-reduction reactions.
40.6 Transaminase vs Dehydrogenase
Transaminase: Transfers amino groups.
Dehydrogenase: Catalyzes oxidation-reduction reactions involving transfer of reducing equivalents.
41. CSIR NET Statement-Based Concepts
41.1 Statement 1
Statement: ATP has the highest phosphoryl-transfer potential among all biological phosphorylated compounds.
Answer: False
PEP and several other phosphorylated compounds have greater phosphoryl-transfer potentials than ATP.
41.2 Statement 2
Statement: PEP can phosphorylate ADP to form ATP.
Answer: True
Pyruvate kinase catalyzes this reaction during glycolysis.
41.3 Statement 3
Statement: SAM is an important biological methyl donor.
Answer: True
SAM participates in methylation of DNA, RNA, proteins, lipids, and metabolites.
41.4 Statement 4
Statement: PLP is required by most transaminases.
Answer: True
PLP is the essential coenzyme for most aminotransferases.
41.5 Statement 5
Statement: Enzymes change the equilibrium constant of a reaction.
Answer: False
Enzymes accelerate both forward and reverse reactions but do not alter the equilibrium constant.
41.6 Statement 6
Statement: Actual cellular ΔG is always equal to ΔG°′.
Answer: False
Actual ΔG depends on the reaction quotient and cellular concentrations.
41.7 Statement 7
Statement: 1,3-BPG can directly transfer its phosphoryl group to ADP.
Answer: True
Phosphoglycerate kinase catalyzes this substrate-level phosphorylation reaction.
42. Important Numerical Concept for CSIR NET
For coupled reactions:
ΔGtotal = ΔG₁ + ΔG₂ + ΔG₃ + …
Suppose:
Reaction 1: ΔG = +15 kJ/mol
Reaction 2: ΔG = −25 kJ/mol
Then:
ΔGtotal = +15 − 25
ΔGtotal = −10 kJ/mol
Therefore, the coupled reaction is thermodynamically favorable.
42.1 Key Rule
When solving CSIR NET thermodynamics questions, always calculate the sum of the free-energy changes for properly coupled reactions.
Never judge the overall reaction only from the ΔG of one individual step.
43. High-Yield Concept — Activated Group Donors
Cells frequently use activated compounds for group transfer.
Important examples are:
ATP → Phosphoryl group
Acetyl-CoA → Acetyl group
SAM → Methyl group
UDP-glucose → Glycosyl group
Aminoacyl-tRNA → Aminoacyl group
43.1 Why Activation Is Necessary
Activation places the transferred group in a chemical environment that makes its transfer feasible.
This is a recurring strategy in biological chemistry:
Chemical activation → Group transfer → Useful biological product
44. Integrated Mechanism of Group Transfer
A group-transfer reaction can be understood through the following sequence.
44.1 Step 1 — Donor Activation
The donor contains the functional group in an activated form.
44.2 Step 2 — Enzyme Recognition
The enzyme recognizes the donor and acceptor.
44.3 Step 3 — Substrate Positioning
The enzyme positions the reacting groups in the correct orientation.
44.4 Step 4 — Group Transfer
The functional group moves from donor to acceptor.
44.5 Step 5 — Product Formation
The acceptor becomes chemically modified.
44.6 Step 6 — Biological Consequence
The modified molecule may:
- Become more reactive.
- Enter another metabolic pathway.
- Become activated.
- Change enzyme activity.
- Change cellular localization.
- Participate in signaling.
- Become incorporated into a macromolecule.
This general framework can be applied to phosphorylation, acetylation, methylation, transamination, glycosylation, and acylation.
45. Major Biological Group-Transfer Reactions
| Reaction type | Major donor | Group | Example |
|---|---|---|---|
| Phosphoryl transfer | ATP | Phosphoryl | Glucose phosphorylation |
| Acetyl transfer | Acetyl-CoA | Acetyl | Citrate formation |
| Methyl transfer | SAM | Methyl | DNA methylation |
| Amino transfer | Amino acid | Amino | Transamination |
| Glycosyl transfer | UDP-glucose | Glycosyl | Glycogen synthesis |
| Acyl transfer | Acyl-CoA | Acyl | Lipid synthesis |
46. Group Transfer and Major Metabolic Pathways
Group transfer is not an isolated topic. It connects several major areas of biochemistry.
46.1 Glycolysis
Important phosphoryl-transfer reactions occur during:
- Glucose phosphorylation
- Fructose phosphorylation
- ATP formation from 1,3-BPG
- ATP formation from PEP
46.2 Citric Acid Cycle
Acetyl-CoA transfers its acetyl group to oxaloacetate.
46.3 Amino Acid Metabolism
Amino groups are transferred between amino acids and keto acids.
46.4 Signal Transduction
Kinases transfer phosphate groups to signaling proteins.
46.5 Nucleic Acid Metabolism
Phosphate-containing nucleotides participate in DNA and RNA synthesis.
46.6 Lipid Metabolism
Acyl-group transfer is essential for lipid synthesis and degradation.
46.7 Carbohydrate Biosynthesis
Glycosyl-group transfer is essential for glycogen and glycoconjugate formation.
47. Rapid Revision Table
| Concept | Must Remember |
|---|---|
| Group transfer | Movement of a functional group between molecules |
| Transferases | Enzymes that catalyze group-transfer reactions |
| ATP | Major phosphoryl donor and energy-coupling molecule |
| PEP | Very high phosphoryl-transfer potential |
| 1,3-BPG | High-energy glycolytic intermediate |
| Phosphocreatine | Rapid ATP buffer |
| Acetyl-CoA | Major acetyl/acyl donor |
| SAM | Major methyl donor |
| PLP | Important coenzyme for amino acid metabolism |
| Transaminase | Amino-group transfer |
| Kinase | Phosphoryl-group transfer |
| Phosphatase | Phosphate removal |
| Glycosyltransferase | Glycosyl-group transfer |
| Substrate-level phosphorylation | Direct phosphoryl transfer to ADP |
| ΔG < 0 | Thermodynamically favorable |
| ΔG = 0 | Equilibrium |
| ΔG > 0 | Thermodynamically unfavorable |
| Enzyme | Lowers activation energy |
| Enzyme and ΔG | Enzymes do not change ΔG |
| ATP hydrolysis | Thermodynamically favorable under standard biochemical conditions |
| Coupling | Overall ΔG is the sum of individual ΔG values |
48. Chapter Summary
Group transfer is a fundamental biochemical process in which a functional group moves from a donor molecule to an acceptor molecule.
The general reaction is:
Donor–Group + Acceptor → Donor + Acceptor–Group
The major transferred groups include:
- Phosphoryl
- Acetyl
- Methyl
- Amino
- Glycosyl
- Acyl
Phosphoryl transfer is especially important in cellular bioenergetics.
ATP is the major cellular phosphoryl donor and energy-coupling molecule, but ATP does not possess the highest phosphoryl-transfer potential among biological phosphorylated compounds.
Important high-transfer-potential compounds include:
PEP
1,3-BPG
Phosphocreatine
ATP
PEP and 1,3-BPG can transfer phosphoryl groups to ADP to produce ATP through substrate-level phosphorylation.
Acetyl-CoA is an important activated acetyl-group donor and a central metabolic intermediate.
SAM is the major biological methyl-group donor.
PLP is an essential coenzyme for many amino acid reactions, especially transamination.
Kinases catalyze phosphoryl-group transfer, while phosphatases catalyze removal of phosphate groups.
The thermodynamic foundation is:
ΔG = ΔG°′ + RT ln Q
For coupled reactions:
ΔGtotal = ΣΔGindividual
Therefore, a favorable reaction can drive an unfavorable reaction when the reactions are appropriately coupled.
For CSIR NET Life Science, the most important associations are:
ATP → Phosphoryl transfer
PEP → Very high phosphoryl-transfer potential
1,3-BPG → Substrate-level phosphorylation
Phosphocreatine → Rapid ATP buffering
Acetyl-CoA → Acetyl-group transfer
SAM → Methyl-group transfer
PLP → Amino-group transfer
Transaminase → Transamination
Kinase → Phosphoryl transfer
Phosphatase → Phosphate removal
Transferase → Group-transfer reaction
A strong understanding of these relationships provides a foundation for solving questions from bioenergetics, glycolysis, metabolism, enzyme mechanisms, thermodynamics, protein regulation, signal transduction, and molecular biology.
