29.2 Catabolism of Triacylglycerols: The Fate of Glycerol
3 min read•may 7, 2024
are broken down through a process called . , special enzymes, chop up these fat molecules into and . This breakdown is crucial for energy production and maintaining our body's fat balance.
The freed-up fatty acids and glycerol don't just sit around. Fatty acids get burned for energy in our cells' powerhouses. Glycerol, on the other hand, can be turned into sugar or used to make more energy. It's all about keeping our body fueled up!
Catabolism of Triacylglycerols
Mechanism of triacylglycerol hydrolysis
Top images from around the web for Mechanism of triacylglycerol hydrolysis
Frontiers | Enhanced Triacylglycerol Production With Genetically Modified Trichosporon oleaginosus View original
Is this image relevant?
Lipid Metabolism | Anatomy and Physiology II View original
Is this image relevant?
Frontiers | Plastidial and ER Triacylglycerol Biosynthesis in a Growth Phase-Dependent Manner in ... View original
Is this image relevant?
Frontiers | Enhanced Triacylglycerol Production With Genetically Modified Trichosporon oleaginosus View original
Is this image relevant?
Lipid Metabolism | Anatomy and Physiology II View original
Is this image relevant?
1 of 3
Top images from around the web for Mechanism of triacylglycerol hydrolysis
Frontiers | Enhanced Triacylglycerol Production With Genetically Modified Trichosporon oleaginosus View original
Is this image relevant?
Lipid Metabolism | Anatomy and Physiology II View original
Is this image relevant?
Frontiers | Plastidial and ER Triacylglycerol Biosynthesis in a Growth Phase-Dependent Manner in ... View original
Is this image relevant?
Frontiers | Enhanced Triacylglycerol Production With Genetically Modified Trichosporon oleaginosus View original
Is this image relevant?
Lipid Metabolism | Anatomy and Physiology II View original
Is this image relevant?
1 of 3
- Lipases catalyze hydrolysis of triacylglycerols into free fatty acids and glycerol (a process known as lipolysis)
- Belong to class contain catalytic triad of serine, histidine, and aspartate/glutamate residues
- Hydrolysis reaction occurs at between fatty acids and glycerol backbone
- Proceeds through two-step mechanism involving
- Serine residue in active site attacks carbonyl carbon of ester bond forming stabilized by
- Tetrahedral intermediate collapses releasing alcohol (glycerol or monoacylglycerol) and forming acyl-enzyme intermediate
- Water molecule attacks acyl-enzyme intermediate forming second tetrahedral intermediate
- Tetrahedral intermediate collapses releasing free fatty acid and regenerating active site serine
- Proceeds through two-step mechanism involving
- Have specific binding sites for fatty acid and glycerol moieties allowing for substrate specificity and
- Can preferentially hydrolyze ester bonds at specific positions on glycerol backbone (sn-1, sn-2, or sn-3)
- Some lipases are specific for short, medium, or long chain fatty acids
- plays a crucial role in regulating lipolysis in
Fate of glycerol after breakdown
- After hydrolysis, glycerol released into cytosol undergoes enzymatic reactions to convert into (DHAP), a glycolytic intermediate
- Glycerol phosphorylated by to form using ATP as phosphate donor
- Glycerol-3-phosphate oxidized by (GPD) to form DHAP
- GPD is NAD-dependent enzyme catalyzes reversible oxidation of glycerol-3-phosphate to DHAP
- Involves transfer of hydride ion () from C2 of glycerol-3-phosphate to NAD forming and DHAP
- DHAP is pathway intermediate can be further metabolized to generate ATP and NADH
- Can be isomerized to (GAP) by (TPI)
- GAP enters glycolytic pathway converting to generating ATP and NADH
- Glycerol can also be converted to glucose via pathway
- Involves conversion of DHAP to by and then to by
- Glucose-6-phosphate can be hydrolyzed to glucose by in liver and kidney
Prochiral nature of glycerol
- Glycerol is molecule has two groups (hydroxyl groups at C1 and C3) can be distinguished by enzyme
- Prochirality arises from presence of (C2) becomes chiral center upon selective modification of one enantiotopic group
- Prochiral nature has implications in enzyme-catalyzed reactions like selective phosphorylation by glycerol kinase
- Glycerol kinase specifically phosphorylates C1 hydroxyl group of glycerol resulting in formation of (L-glycerol-3-phosphate)
- Distinguishes between two enantiotopic hydroxyl groups selectively modifying one over other
- Stereospecific phosphorylation of glycerol by glycerol kinase is example of enzymatic prochiral selectivity
- Arises from unique three-dimensional structure of enzyme's active site allows for specific recognition and binding of one enantiotopic group over other
- Selective modification of prochiral molecules by enzymes is crucial in many biochemical pathways
- Leads to formation of chiral products with specific stereochemistry that can impact biological functions
- Examples include stereospecific reduction of prochiral ketones by alcohol dehydrogenases and selective hydrolysis of prochiral esters by lipases and esterases
Fate of Fatty Acids
- Free fatty acids released during lipolysis undergo in mitochondria
- In conditions of prolonged fasting or diabetes, excessive fatty acid oxidation can lead to the production of
- Adipose tissue serves as the primary storage site for triacylglycerols and plays a crucial role in energy homeostasis
Key Terms to Review (39)
Acyl-enzyme Intermediate: An acyl-enzyme intermediate is a transient covalent complex formed during enzymatic reactions, where the enzyme's active site temporarily binds to an acyl group from a substrate. This intermediate plays a crucial role in the catalytic mechanism of certain enzymes, particularly those involved in the hydrolysis or synthesis of ester, amide, or peptide bonds.
Adipose Tissue: Adipose tissue, commonly known as body fat, is a specialized connective tissue that primarily functions as an energy storage depot. It plays a crucial role in the catabolism of triacylglycerols and the fate of glycerol within the body.
Aldolase: Aldolase is a class of enzymes that catalyze the reversible aldol addition reaction, which is a key step in both the catabolism and anabolism of carbohydrates and lipids. This enzyme plays a crucial role in the glycolytic pathway, gluconeogenesis, and the breakdown of triacylglycerols, making it a central player in cellular energy metabolism.
ATP (Adenosine Triphosphate): ATP, or adenosine triphosphate, is the primary energy currency of living cells. It is a high-energy nucleotide that stores and transfers the energy needed to power various cellular processes, from muscle contraction to protein synthesis. ATP is central to the understanding of bond dissociation energies, biological substitution reactions, metabolism, and energy production in the body.
Beta-Oxidation: Beta-oxidation is the metabolic pathway by which fatty acids are broken down to generate acetyl-CoA, which can then enter the citric acid cycle to produce ATP. It is a crucial process in the catabolism of triacylglycerols and the biosynthesis of fatty acids.
Dihydroxyacetone Phosphate: Dihydroxyacetone phosphate is a key intermediate in several important metabolic pathways, including the catabolism of triacylglycerols, the catabolism of carbohydrates through glycolysis, and certain biological carbonyl condensation reactions. It serves as a critical link between these diverse metabolic processes.
Enantiotopic: Enantiotopic refers to the relationship between two identical substituents or groups on a prochiral molecule that, if replaced, would result in the formation of enantiomeric products. This concept is crucial in understanding the stereochemical outcomes of chemical reactions involving prochiral substrates.
Ester Bonds: An ester bond is a type of covalent chemical bond formed between a carboxylic acid and an alcohol, resulting in the creation of an ester compound. These bonds are essential in the structure and function of various organic molecules, including polyesters and triacylglycerols.
Fatty Acids: Fatty acids are long-chain carboxylic acids that are the primary components of fats and oils. They play a crucial role in various biological processes, including energy storage, cell membrane structure, and signaling pathways, which are relevant to the topics of waxes, fats, and oils, soap, metabolism, and the catabolism of triacylglycerols.
Fructose-1,6-bisphosphatase: Fructose-1,6-bisphosphatase is a key enzyme in the gluconeogenesis pathway that catalyzes the hydrolysis of fructose-1,6-bisphosphate to fructose-6-phosphate, an important step in the regulation of blood glucose levels.
Fructose-1,6-bisphosphate: Fructose-1,6-bisphosphate is a key intermediate in several important metabolic pathways, including the catabolism of triacylglycerols, the catabolism of carbohydrates through glycolysis, and the biosynthesis of carbohydrates via gluconeogenesis. It is an essential molecule that links these diverse metabolic processes together.
Gluconeogenesis: Gluconeogenesis is the metabolic process by which the body synthesizes glucose from non-carbohydrate precursors, such as amino acids, lactate, and glycerol. It is an important pathway that helps maintain blood glucose levels, especially during periods of fasting or starvation when glucose availability is limited.
Glucose-6-phosphatase: Glucose-6-phosphatase is an enzyme that catalyzes the final step in gluconeogenesis, the process of synthesizing glucose from non-carbohydrate precursors. It plays a crucial role in regulating blood glucose levels and maintaining glucose homeostasis in the body.
Glucose-6-Phosphate: Glucose-6-phosphate is a crucial metabolic intermediate that serves as a key junction point in carbohydrate metabolism, linking various metabolic pathways such as glycolysis, glycogen synthesis, and the pentose phosphate pathway.
Glyceraldehyde-3-Phosphate: Glyceraldehyde-3-phosphate, also known as G3P or GAP, is a crucial intermediate in several metabolic pathways, including glycolysis, the Calvin cycle, and the catabolism of triacylglycerols. It is a three-carbon sugar phosphate that serves as a key branch point in cellular energy production and biosynthesis.
Glycerol: Glycerol, also known as glycerin, is a simple sugar alcohol that plays a crucial role in various biochemical processes related to fats, oils, and energy metabolism. This three-carbon compound is a key component in the structure of triacylglycerols, the primary storage form of lipids in the body, and is also involved in the production and utilization of energy through its participation in metabolic pathways.
Glycerol kinase: Glycerol kinase is an enzyme that catalyzes the phosphorylation of glycerol to glycerol 3-phosphate, a key step in the catabolism of triacylglycerols and the subsequent utilization of glycerol for energy production or other metabolic processes.
Glycerol-3-phosphate: Glycerol-3-phosphate is a key intermediate in the catabolism of triacylglycerols, serving as a precursor for the synthesis of phospholipids and other important lipid molecules within the body.
Glycerol-3-phosphate dehydrogenase: Glycerol-3-phosphate dehydrogenase is an enzyme that catalyzes the reversible conversion of glycerol-3-phosphate to dihydroxyacetone phosphate, a key step in the catabolism of triacylglycerols and the metabolism of glycerol.
Glycolysis: Glycolysis is the metabolic pathway that converts glucose, a six-carbon sugar, into two molecules of pyruvate, a three-carbon compound. This process is the first step in the catabolism of carbohydrates and is a fundamental part of cellular respiration, providing energy in the form of ATP to the cell.
Hormone-Sensitive Lipase: Hormone-sensitive lipase is an enzyme that plays a crucial role in the catabolism of triacylglycerols, the primary form of stored fat in the body. It is responsible for the hydrolysis of triacylglycerols, releasing fatty acids and glycerol that can be used for energy production or other metabolic processes.
Ketone Bodies: Ketone bodies are a group of three water-soluble molecules (acetoacetate, beta-hydroxybutyrate, and acetone) that are produced by the liver as a byproduct of the breakdown of fatty acids through a process called beta-oxidation. They serve as an alternative energy source when glucose is scarce, such as during fasting or starvation.
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.
Lipolysis: Lipolysis is the metabolic process by which lipids, or fats, are broken down into smaller molecules, such as fatty acids and glycerol, through the action of lipase enzymes. This process is a crucial component of the catabolism of triacylglycerols, which are the primary storage form of energy in the body.
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.
NADH: NADH, or nicotinamide adenine dinucleotide, is a coenzyme that plays a crucial role in numerous metabolic processes within the body. It is the reduced form of NAD+, an important electron carrier that is involved in oxidation-reduction reactions throughout the cell's energy-producing pathways.
Oxyanion Hole: The oxyanion hole is a structural feature found in the active sites of many enzymes that catalyze reactions involving the formation or cleavage of ester, amide, or other bonds. It provides a specialized binding site that stabilizes the negatively charged transition state or intermediate that occurs during these reactions.
Polyunsaturated fatty acids: Polyunsaturated fatty acids are a type of fat found in oils from plants and some fish, containing more than one double bond in their hydrocarbon chain. These acids are crucial for human health, influencing inflammation and cell membrane integrity.
Prochiral: Prochirality refers to the property of a molecule that has two enantiotopic groups or faces that are not related by any symmetry operation. In other words, a prochiral molecule has the potential to become chiral upon the introduction of a new substituent or functional group.
Prochirality center: A prochirality center is a carbon atom in a molecule that can be converted from achiral to chiral with a single substitution. It essentially has the potential to become a stereocenter upon modification of its environment or substituents.
Pyruvate: Pyruvate is a key intermediate molecule in cellular metabolism, serving as a central hub that connects various metabolic pathways. It is the final product of glycolysis, the process of breaking down glucose to generate ATP, and plays a crucial role in energy production, biosynthesis, and other essential metabolic processes within the body.
Regioselectivity: Regioselectivity refers to the preference of a chemical reaction to occur at a specific site or region of a molecule, leading to the formation of one regioisomeric product over another. This concept is particularly important in the context of electrophilic addition reactions of alkenes, electrophilic aromatic substitution, and other organic transformations.
Serine Hydrolases: Serine hydrolases are a class of enzymes that catalyze the hydrolysis of ester, amide, or thioester bonds in a wide range of substrates. They play a crucial role in various biological processes, including the catabolism of triacylglycerols and the regulation of glycerol metabolism.
Sn-glycerol-3-phosphate: sn-glycerol-3-phosphate, also known as glycerol 3-phosphate, is a key intermediate in the catabolism of triacylglycerols (fats). It is formed during the breakdown of glycerol, a component of triacylglycerols, and serves as a precursor for the synthesis of phospholipids and other important biomolecules.
Stereogenic center: A stereogenic center in a molecule is an atom, typically carbon, that is attached to four different groups or atoms, allowing the molecule to exist in two or more spatial arrangements (stereoisomers). These centers are crucial for the molecule's three-dimensional shape and properties.
Stereogenic Center: A stereogenic center, also known as a chiral center, is an atom within a molecule that has four different substituents attached to it, resulting in the formation of two non-superimposable mirror images, or enantiomers. This concept is central to understanding the stereochemistry of organic molecules and their behavior in various chemical reactions.
Tetrahedral Intermediate: A tetrahedral intermediate is a key reaction step that occurs in many organic chemistry reactions, where a trigonal planar carbonyl carbon temporarily becomes a tetrahedral carbon with four bonded atoms. This transient intermediate is crucial for understanding the mechanisms of various nucleophilic addition and substitution reactions.
Triacylglycerols: Triacylglycerols, also known as triglycerides, are the primary storage form of lipids in the body. They are composed of three fatty acid molecules esterified to a glycerol backbone, serving as an efficient way to store and transport energy.
Triose Phosphate Isomerase: Triose phosphate isomerase is an enzyme that catalyzes the interconversion of the triose phosphate isomers dihydroxyacetone phosphate (DHAP) and D-glyceraldehyde 3-phosphate (G3P) in the glycolysis pathway. This interconversion is a critical step in the catabolism of triacylglycerols and the fate of glycerol.