26.10 Enzymes and Coenzymes
3 min read•may 7, 2024
Enzymes are nature's powerhouses, speeding up chemical reactions in our bodies. They're like tiny molecular machines, each designed to do a specific job, making life's processes possible.
These biological catalysts come in six main types, each with a unique role. From breaking down food to building DNA, enzymes often need helper molecules called cofactors and coenzymes to get the job done.
Enzyme Structure and Function
Enzyme function as catalysts
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- Enzymes are biological catalysts that accelerate chemical reactions in living organisms without being consumed or permanently altered
- Speed up reactions by factors of to compared to uncatalyzed reactions allowing them to occur at physiologically relevant rates
- Highly specific catalyzing only one or a few similar reactions due to the unique three-dimensional structure of the 's
- Lower the () of a reaction the minimum energy required for reactants to form products
- Allows more reactant molecules to have sufficient energy to overcome the energy barrier and form products
- Do not alter the equilibrium of the reaction only the rate at which equilibrium is reached
- Exhibit , recognizing and binding to specific substrates
Classification system for enzymes
- The International Union of Biochemistry and Molecular Biology (IUBMB) classifies enzymes into six main categories based on the type of reaction they catalyze:
- : catalyze oxidation-reduction reactions
- oxidizes ethanol to acetaldehyde
- : transfer functional groups from one molecule to another
- transfer amino groups
- : catalyze hydrolysis reactions breaking bonds using water
- hydrolyze triglycerides into fatty acids and glycerol
- : catalyze non-hydrolytic addition or removal of groups from substrates
- remove carboxyl groups from amino acids
- : catalyze isomerization reactions intramolecular rearrangements
- converts glucose to fructose
- : catalyze the formation of covalent bonds coupling the hydrolysis of ATP
- joins DNA fragments during replication and repair
- : catalyze oxidation-reduction reactions
Enzyme Kinetics and Regulation
- describes the relationship between concentration and reaction rate
- occurs when molecules bind to enzymes and decrease their activity
- involves binding of molecules to sites other than the , affecting enzyme activity
Cofactors and Coenzymes
Cofactors vs coenzymes in enzyme function
- Cofactors are non-protein molecules required for enzyme activity
- Can be inorganic metal ions (, , ) or organic coenzymes
- Assist in enzyme function by participating in the catalytic mechanism or maintaining the enzyme's structure
- Coenzymes are organic non-protein molecules that participate in enzymatic reactions
- Often derived from vitamins (NAD from niacin, from riboflavin)
- Serve as electron carriers (NAD, FAD), group transfer molecules (, ), or activation energy lowering agents ()
- Not permanently bound to the enzyme and can dissociate after the reaction
- Can be regenerated and recycled to participate in multiple enzymatic reactions
- Enzymes that require cofactors or coenzymes are called holoenzymes
- The protein portion of the enzyme without the is called the
Key Terms to Review (32)
Activation Energy: Activation energy is the minimum amount of energy required to initiate a chemical reaction. It represents the energy barrier that reactants must overcome in order to form products. This concept is central to understanding the mechanisms and kinetics of organic reactions.
Activation energy, ΔG‡: Activation energy (ΔG‡) is the minimum amount of energy required to initiate a chemical reaction, specifically the energy needed to reach the transition state from the reactants. It's a crucial factor in determining the rate at which a reaction will occur in organic chemistry.
Active site: The active site is the specific region on an enzyme where substrate molecules bind and undergo a chemical reaction. It is characterized by its unique arrangement of amino acids that create a highly selective and efficient catalyst for biological transformations.
Active Site: The active site is a specific region on an enzyme molecule where the substrate binds and the catalytic reaction occurs. It is the functional center of the enzyme, responsible for its unique catalytic activity.
Alcohol Dehydrogenase: Alcohol dehydrogenase (ADH) is an enzyme that catalyzes the oxidation of alcohols to aldehydes or ketones. It plays a crucial role in the metabolism of ethanol and other alcohols in the body, as well as in the regulation of chiral environments and the catalysis of enzymatic reactions.
Allosteric Regulation: Allosteric regulation is a mechanism by which the activity of an enzyme or protein is modulated by the binding of an effector molecule at a site other than the active site. This regulatory process allows enzymes to respond to changes in the cellular environment and adjust their catalytic activity accordingly.
Aminotransferases: Aminotransferases, also known as transaminases, are a class of enzymes that catalyze the transfer of amino groups from one molecule to another. These enzymes play a crucial role in the metabolism of amino acids and the regulation of nitrogen balance within the body.
Apoenzyme: An apoenzyme is the protein component of an enzyme that requires an additional non-protein cofactor, known as a coenzyme, to become fully active and carry out its catalytic function. The apoenzyme alone is inactive, but when combined with its specific coenzyme, it forms the complete, functional enzyme.
Catalyst: A catalyst is a substance that increases the rate of a chemical reaction without being consumed or altered itself. Catalysts work by providing an alternative pathway for the reaction, which lowers the activation energy required and allows the reaction to proceed more quickly.
Coenzyme: A coenzyme is a small organic molecule that binds to an enzyme and is essential for its catalytic activity. Coenzymes work in conjunction with enzymes to facilitate and enhance specific chemical reactions in the body.
Coenzyme A: Coenzyme A (CoA) is a critical cofactor involved in numerous metabolic pathways, including the breakdown and synthesis of carbohydrates, fats, and amino acids. It plays a central role in connecting various biological reactions and serves as an essential component in the Citric Acid Cycle, the biosynthesis of fatty acids, and the activation of carboxylic acids.
Cofactor: A cofactor is a non-protein chemical compound or metallic ion that is required for an enzyme's catalytic activity. Cofactors work in conjunction with enzymes to facilitate and enhance specific chemical reactions within the body, particularly those involved in metabolism and energy production.
Decarboxylases: Decarboxylases are a class of enzymes that catalyze the removal of a carboxyl group (COOH) from a substrate, typically resulting in the production of carbon dioxide and a new compound. These enzymes play a crucial role in various metabolic pathways, particularly in the context of enzymes and coenzymes.
DNA Ligase: DNA ligase is an enzyme that catalyzes the formation of phosphodiester bonds between adjacent DNA fragments, effectively sealing breaks in the DNA backbone. It is a crucial enzyme involved in various DNA repair and replication processes.
Enzyme: Enzymes are biological catalysts that accelerate chemical reactions in living organisms without being consumed or altered themselves. They play a crucial role in facilitating and regulating the vast array of metabolic processes that sustain life.
Enzyme Specificity: Enzyme specificity refers to the ability of an enzyme to recognize and bind to a specific substrate or set of substrates, catalyzing a particular chemical reaction. This selective binding and catalysis is a fundamental property of enzymes that allows them to function efficiently within the complex biochemical environment of the cell.
FAD: FAD, or Flavin Adenine Dinucleotide, is a coenzyme that plays a crucial role in various metabolic processes within the body. It serves as an essential cofactor for numerous enzymes involved in energy production, oxidation-reduction reactions, and other vital biochemical pathways.
Glucose Isomerase: Glucose isomerase, also known as xylose isomerase, is an enzyme that catalyzes the reversible isomerization of glucose to fructose. It plays a crucial role in the conversion of glucose to fructose, an important process in both the context of essential monosaccharides and enzymatic reactions.
Holoenzyme: A holoenzyme is the complete, functional enzyme that consists of both the protein component (apoenzyme) and the necessary cofactor(s) (coenzyme or prosthetic group). It is the active form of the enzyme that can catalyze a specific chemical reaction in the body.
Hydrolases: Hydrolases are a class of enzymes that catalyze the hydrolysis, or breaking down, of chemical bonds in various substrates through the addition of water molecules. They play a crucial role in the metabolism and digestion of organic compounds.
Inhibition: Inhibition is a process in which a substance or mechanism reduces or prevents the activity of an enzyme or other biological process. It is a crucial regulatory mechanism that allows organisms to control and fine-tune their metabolic and physiological functions.
Isomerases: Isomerases are a class of enzymes that catalyze the interconversion of isomeric molecules. They play a crucial role in the rearrangement of molecular structures within the context of enzymes and coenzymes, allowing for the transformation of one isomer into another without changing the molecular formula.
Ligases: Ligases are a class of enzymes that catalyze the joining or ligation of two molecules by forming a new chemical bond. They play a crucial role in various metabolic processes, particularly in the context of enzymes and coenzymes.
Lipases: Lipases are enzymes that catalyze the hydrolysis of lipids, such as fats and oils, into smaller components like fatty acids and glycerol. They play a crucial role in the catabolism of triacylglycerols and the regulation of lipid metabolism within the body.
Lyases: Lyases are a class of enzymes that catalyze the addition or removal of chemical groups from a molecule without the use of water or oxygen. They are responsible for the cleavage of carbon-carbon, carbon-oxygen, and carbon-nitrogen bonds through non-hydrolytic and non-oxidative mechanisms.
Michaelis-Menten Kinetics: Michaelis-Menten kinetics is a model that describes the rate of enzymatic reactions, specifically the relationship between the concentration of a substrate and the rate of product formation. It provides a framework for understanding the kinetic behavior of enzymes and how they catalyze chemical reactions in biological systems.
NAD+: NAD+ (Nicotinamide Adenine Dinucleotide) is an essential coenzyme involved in numerous metabolic processes within the body. It plays a crucial role in the oxidation of organic compounds, serving as an electron acceptor in various redox reactions.
Oxidoreductases: Oxidoreductases are a class of enzymes that catalyze oxidation-reduction (redox) reactions, where one substrate is oxidized while another is reduced. They are crucial in biological reductions and play a central role in the regulation of enzyme activity through coenzyme binding.
S-adenosylmethionine: S-adenosylmethionine (SAM-e) is a versatile cofactor and methyl donor found in all living cells. It plays a crucial role in various metabolic processes, including methylation reactions, polyamine synthesis, and the regulation of gene expression.
Substrate: In the context of organic chemistry, a substrate is the molecule or compound that undergoes a chemical reaction, typically catalyzed by an enzyme or a reagent in a laboratory setting. Substrates serve as the starting material for various types of reactions, including biological reactions and laboratory reactions.
Thiamine Pyrophosphate: Thiamine pyrophosphate (TPP), also known as thiamine diphosphate (ThDP), is an essential cofactor required for the proper functioning of several enzymes involved in carbohydrate metabolism and energy production. It is the active form of the vitamin thiamine, also called vitamin B1, and plays a crucial role in the context of enzymes and the citric acid cycle.
Transferases: Transferases are a class of enzymes that catalyze the transfer of functional groups from one molecule to another. They play a crucial role in various metabolic processes by facilitating the movement of chemical moieties between substrates, thereby enabling essential biochemical transformations in the body.