The food shown here are those that we consume which are comprised of macronutrients like carbohydrates, proteins, and fats. A healthy diet comprises all of these nutrients as well as minerals, vitamins, and electrolytes. Our body breaks down food in a process called metabolism and the process in which our body transfers energy is called bioenergetics.
Learning Objectives
Explain the concept of bioenergetics and its importance in cellular functions.
State and explain the first and second laws of bioenergetics.
Illustrate how energy is converted and transferred within the body, including examples of exergonic and endergonic reactions.
Describe the structure and function of the cell membrane, mitochondria, nucleus, and cytoplasm.
Define metabolism and explain the role of metabolic pathways in energy production.
Identify the primary substrates used for energy during exercise and describe their metabolic pathways.
Classify different types of enzymes and describe their specific roles in metabolic reactions.
Explain the concept of enzyme specificity and the “induced fit” model of enzyme action.
Define coenzymes and describe their role in assisting enzymatic reactions.
Explain the importance of high-energy phosphate molecules like ATP and creatine phosphate in energy transfer.
Discuss how an understanding of bioenergetics can inform exercise professionals about muscle energy generation and body responses to exercise.
Bioenergetics
All living organisms require energy that is generated through chemical reactions. At any given moment, thousands of these reactions are occurring within your cells, enabling your body to produce the energy necessary for sustaining life. This energy can also be stored and used during activities such as physical exercise. Ultimately, all energy on Earth originates from the sun. Plants transform solar energy into carbohydrates, fats, and proteins through photosynthesis. Animals then consume these plants, or other animals, to obtain the energy needed for cellular functions.
Bioenergeticsis a branch of biochemistry that examines the flow of energy from one source to another. It explores how foodstuffs are converted into adenosine triphosphate (ATP), the primary energy currency of cells (Figure 3.1). This process is crucial for understanding how organisms’ harness and utilize energy to maintain life.
Figure 3.1 Conceptual diagram providing an overview of bioenergetics.
Understanding bioenergetics is crucial because it provides the foundational principles by which metabolism operates. Comprehending metabolism is essential for exercise professionals to understand how skeletal muscles generate energy and how the body responds to exercise. Without a thorough grasp of energy flow within the body, it is impossible to fully understand skeletal muscle functions both at rest and during exercise. Metabolism encompasses the chemical reactions responsible for the creation and transfer of energy necessary to sustain exercise.
There are two fundamental laws of bioenergetics that govern metabolic processes. The first law states that 1)energy cannot be created or destroyed but is converted from one form to another. In the human body, various reactions convert chemical, electrical, mechanical, and thermal energies into different forms. For instance, light entering the eyes is transformed into a chemical signal, which is then converted into electrical action potentials in the brain. Muscles convert chemical energy (ATP) into mechanical energy during muscle contractions, which can be used to exert force on the external environment. The bioenergetic process of energy conversion involves a series of tightly regulated chemical reactions that release energy stored in the chemical bonds of molecules. Ultimately, all energy is eventually transformed into heat.
The second law of bioenergetics states that 2) energy transfer will proceed in the direction of increased entropy and the release of free energy. Potential energy is stored in the bonds of molecules, referred to as “high energy” bonds. When these bonds are broken, they release a specific amount of energy known as free energy (ΔG), typically measured in calories per mole. For example, the complete oxidation of one mole of glucose releases 686,000 calories[1]. Cells harvest this free energy to perform work, or it can be lost as heat. In thermodynamics, entropy describes the unavailability of a system’s thermal energy for conversion into mechanical work and can also be interpreted as the degree of disorder or randomness in a system. When converting a substrate to a product, by-products such as heat, light, entropy, and free energy are often produced.
Cellular Chemical Reactions
Chemical reactions within cells are categorized into two major types that work together to sustain energy flow. Exergonic (or exothermic) reactions release free energy, such as those involved in glucose breakdown. The energy liberated from exergonic reactions can drive other reactions. Conversely, endergonic (or endothermic) reactions require an input of energy to proceed. When energy is added to an endergonic reaction, the resulting products contain more free energy than the original substrates.
Exergonic and endergonic reactions are often linked in a process known as coupled reactions. In coupled reactions, the free energy released from an exergonic reaction is used to drive an endergonic reaction. This systematic linking of reactions ensures the efficient transfer and utilization of energy within cells. An example of coupled reactions is illustrated in figure 3.2 where the same energy that is liberated from reaction 1, is then used to initiate reaction 2.
Figure 3.2 Coupled Reactions. Reaction 1 is an exergonic reaction in which substrates A and B are converted into products C and D, releasing free energy. This liberated energy is then used to drive Reaction 2, an endergonic process where substrates E and F are converted into products G and H. Arrows indicate the direction of each reaction, and a connecting line or symbol shows the energy transfer between them. The figure demonstrates how energy-releasing reactions can power energy-requiring processes, a fundamental principle in cellular metabolism.
Redox reactions
Reduction-oxidation (redox) reactionsinvolve the transfer of electrons between two molecules. These reactions are essential to many fundamental life processes, including photosynthesis, respiration, combustion, and metabolism. When a molecule gains electrons, it undergoes a reduction reaction. Conversely, when a molecule loses electrons, it undergoes an oxidation reaction. A helpful mnemonic to remember this is “LEO the lion says GER,” which stands for “Loss of Electrons is Oxidation” and “Gain of Electrons is Reduction.”
It is important to note that electrons are not free-floating; they are attached to other molecules by their charge. In many metabolic steps, electrons that are removed are bound to a proton (hydrogen). Figure 3.3 illustrates a hydrogen atom, which consists of a proton and a valence electron. Redox reactions involving hydrogen atoms occur in several stages of catabolism. When hydrogen is removed, a carrier molecule transports the hydrogen (a proton and an electron) to later stages in metabolism. These molecules, known as “electron carriers,” will be discussed further in the co-enzyme section of this chapter.
Figure 3.3 A hydrogen atom is composed of a positively charged proton and a negatively charged electron.
Energy Transfer and Cell Anatomy
Energy transfer occurs within the cells of the body, making an understanding of cell anatomy vital to the study of bioenergetics. Cells were first discovered in the seventeenth century by the English natural philosopher Robert Hooke. Over the past 300 years, advancements in cell microscopy have significantly enhanced our understanding of cell structure. We now know that organisms are primarily composed of four elements: oxygen (65%), carbon (18%), hydrogen (10%), and nitrogen (3%)[2]. These elements make up more than 95% of the human body. Additional chemical substances found in the body include sodium, iron, zinc, potassium, magnesium, chloride, and calcium.
Molecules that contain carbon are known as organic compounds and are often linked with other elements by chemical bonds. For example, glucose (C6H12O6) is an organic molecule and serves as a source of energy classified as a carbohydrate. In contrast, inorganic compounds are molecules that do not contain carbon atoms. Water (H2O), for instance, does not contain carbon atoms and is therefore classified as inorganic.
Figure 3.4 The basic structure of a muscle cell (fiber) and its major organelles. The elongated, cylindrical cell is shown with multiple peripheral nuclei and a surrounding sarcolemma (cell membrane). Inside, longitudinally arranged myofilaments are visible, composed of repeating sarcomeres—the contractile units. Mitochondria are scattered throughout the sarcoplasm, indicating sites of ATP production. The diagram emphasizes the structural and functional organization of muscle cells in relation to contraction and energy metabolism.
Cells are highly organized units compartmentalized into smaller organelles that carry out necessary functions. While not all cells have the same function, they share structural similarities. Each cell is surrounded by a semi-permeable membrane composed of a phospholipid bilayer with both hydrophobic and hydrophilic properties. This cell membrane, known as the sarcolemma in skeletal muscle, protects the cell from the external environment and provides structural compartments to house the cell’s inner contents.
The nucleus is a large, rounded body within the cell that contains the organism’s genetic material in the form of deoxyribonucleic acid (DNA). DNA contains genes that code for proteins, regulating protein synthesis, which determines cell composition and controls cellular activity. Muscle cells, also known as muscle fibers, are unique in that they are multi-nucleated, meaning they have more than one nucleus.
Another major component of the cell is the cytoplasm, or sarcoplasm in muscle cells. The cytoplasm, also referred to as the cytosol, contains various organelles, including the mitochondria. Mitochondria, often called the powerhouse of the cell, are heavily involved in creating energy from foodstuffs. They are particularly important in skeletal muscle bioenergetics and metabolism due to their role in energy generation. Additionally, the sarcoplasm contains essential proteins such as actin and myosin, which promote organization and prevent structural collapse. Actin and myosin form structures called myofilaments within the muscle cell, providing rigid scaffolding for structure and the ability to produce force. Figure 3.4 illustrates the basic structures of a muscle fiber.
Metabolism
A significant proportion of chemical reactions in cells occur to create energy from food, which is then used to perform cellular work. These reactions are termed metabolism and are required to maintain life. Metabolism is typically divided into two categories. Catabolism refers to reactions that breakdown molecules to release energy and anabolism are those reactions that synthesize molecules to form larger molecules. Anabolism requires energy to be inputed into the reaction.
Energy is required for muscle activity, gland secretion, maintenance of nerve and muscle fiber membrane potentials, synthesis of substances in cells, absorption of food from the gastrointestinal tract, and many other functions[3]. A substrate is any substance acted upon by enzymes to create a product molecule. The three forms of usable nutrients in the human body are carbohydrates, proteins, and fats. When consumed, these nutrients are metabolized and used as substrates to create usable cellular energy. A metabolic pathway is a sequence of enzyme-mediated chemical reactions that convert substrates to products.
During exercise, the primary substances used for energy generation are fats and carbohydrates, with minimal energy contribution from protein metabolism. Therefore, carbohydrate and fat metabolism will be highlighted in this text, along with an explanation of the relationship between carbohydrate, fat, and protein metabolism.
Substrates Used for Energy
Carbohydrates are synthesized during photosynthesis by plants from the interaction of CO2, water, and solar energy. Composed of carbon (C), hydrogen (H), and oxygen (O2), carbohydrates exist as monosaccharides, disaccharides, or polysaccharides. Monosaccharides are simple sugars such as fructose and glucose. All carbohydrates are ultimately converted to glucose, which is transported through the blood to all body tissues. Glucose is the preferred carbohydrate for muscles due to its high availability in the blood and the substantial energy yield it provides. Glucose yields approximately 4 kcal of energy per gram and has the chemical formula C6H12O6.
Muscle cells can store small amounts of glucose in the form of glycogen, a polysaccharide also stored in the liver. Glycogen is synthesized within cells by linking single glucose molecules together with the enzyme glycogen synthase. Glycogen molecules can consist of hundreds to thousands of glucose molecules. Carbohydrate stores in the liver and skeletal muscle are limited to about 2,500 to 2,600 kcal of energy, equivalent to the energy needed for approximately 25 miles (40 km) of running[4].
Figure 3.5 The molecular structure of glucose. A glucose molecule is a six-carbon monosaccharide with the molecular formula C₆H₁₂O₆. The image shows glucose in its cyclic (pyranose) form, with a six-membered ring composed of five carbon atoms and one oxygen atom. Each carbon is bonded to hydrogen and hydroxyl (–OH) groups in a specific orientation, distinguishing D-glucose as a biologically active isomer. The diagram includes labels for carbon atoms (C1–C6), and hydroxyl groups, highlighting the molecule’s role in energy metabolism and cellular respiration.
Fructose, another monosaccharide, is the sweetest of the carbohydrates and is found in fruits and honey. Disaccharides are formed when two monosaccharides combine. A common example is table sugar, or sucrose, which consists of glucose and fructose. Sucrose is the most common dietary disaccharide in the United States, accounting for nearly 25% of the total caloric intake for most Americans[5]. Polysaccharides, which are complex carbohydrates, contain three or more monosaccharides. Cellulose and starch are two forms of polysaccharides; however, humans lack the enzymes to digest cellulose, which is excreted as waste. Starch, found in corn, beans, grains, and peas, is easily digested and constitutes a significant portion of the human diet[6]. It is recommended that adults obtain 45% to 65% of their calories from carbohydrates[7].
Fats are also a preferred substrate for energy production during exercise, providing a substantial portion of the energy used during prolonged, less intense activities. Fats contain the same chemical elements as carbohydrates, but with a higher ratio of carbon to oxygen. This higher ratio allows fats to yield more energy per gram than carbohydrates, with 1 gram of fat providing approximately 9 kcal of energy, roughly double that of carbohydrates. Fats are generally classified into three groups: triglycerides, phospholipids, and steroids.
Triglyceridesconsist of three fatty acid chains and one glycerol molecule. Fatty acids, the primary fats used by muscles for metabolism, are stored in the body as triglycerides. They are released into the bloodstream through a process called lipolysis, which is regulated by enzymes known as lipases. The glycerol molecule can be used by the liver to synthesize glucose if necessary. Phospholipids, which make up the cell membrane’s phospholipid bilayer, provide structural integrity for cells but are not used as an energy source. Steroids, derived from dietary cholesterol, are components of cell membranes and are necessary for synthesizing sex hormones. Nutritional guidelines recommend that adults obtain 20% to 35% of their calories from fat[8].
Proteins are not a major energy source during exercise but can be used under certain conditions. To be used for energy, proteins must be converted to glucose through gluconeogenesis or to free fatty acids through lipogenesis in cases of severe energy depletion or starvation. Proteins are composed of amino acids, which can be broken down through deamination. There are 20 amino acids needed by the body to synthesize proteins, tissues, and enzymes, nine of which are essential and must be obtained from food. Proteins can also become intermediates in metabolism to help generate ATP. It is recommended that adults obtain 10% to 35% of their calories from protein[9].
Enzymesare biological catalysts that increase the speed of metabolic pathways without becoming part of the final product (Figure 3.6). Chemical reactions occur only when the reacting molecules have sufficient initial free energy, or activation energy, to start the reaction. Enzymes lower the activation energy required, thereby conserving energy and improving reaction time. Many enzymes facilitate the breakdown (catabolism) of chemical compounds. All enzymes are proteins that act upon a substrate to create a product. They are highly specific, interacting only with their designated substrate to form an enzyme-substrate (E-S) complex. This complex temporarily changes shape to facilitate the reaction, after which the enzyme returns to its original shape, remaining virtually unaltered. This process is known as the “induced fit” model of enzyme action. Enzymes rely on maintaining their correct conformation, which can be affected by temperature and pH. The major characteristics of enzymes are listed in Table 3.1.
Table 3.1 A summary of the major characteristics of enzymes
Major characteristics of enzymes
Proteins
Specific
Unaltered
Affected by temperature
Affected by pH
Facilitate the reaction
Other cellular constituents, such as ATP, can regulate enzyme activity. Enzymes can be inhibited through negative feedback, slowing the overall rate of the reaction or pathway. Rate-limiting enzymes, typically found early in the pathway, can be inhibited or stimulated. Allosteric enzymes, which bind to effectors, can either stimulate or inhibit enzyme activity at the active site. These enzymes are major regulators of metabolic pathways.
Figure 3.6 The enzyme-substrate complex mechanism of enzymes.
Classification of Enzymes
Enzymes play a crucial role in energy transfer and control the rate of free-energy release. Metabolic pathways that produce a product from a substrate typically involve multiple steps, each catalyzed by a specific enzyme with a specific function. Enzymes are named based on their role in rearranging, adding, or cleaving sub-molecules during a reaction.
Kinases: These enzymes add a phosphate group to a molecule.
Dehydrogenases: These enzymes remove hydrogen atoms, such as lactate dehydrogenase.
Oxidases: These enzymes catalyze redox reactions involving oxygen.
Isomerases: These enzymes rearrange molecular substances.
Most enzymes have names ending in “-ase.” Additionally, many enzymes require other molecules called coenzymes or cofactors to function.
Coenzymes, also known as cofactors, are non-protein organic substances that assist enzymes. They act as temporary carriers of products and are often considered “helper molecules” in biochemical transformations. The availability of coenzymes can affect enzymatic function and the rate of metabolic reactions. Dietary coenzymes are derived from vitamins. Two important coenzymes in metabolism are Nicotinamide Adenine Dinucleotide (NAD+) and Flavin Adenine Dinucleotide (FAD). NAD+ is derived from niacin (vitamin B3), while FAD comes from riboflavin (vitamin B2). Both NAD+ and FAD are electron carriers essential for ATP production.
High-Energy Phosphates
High-energy phosphate molecules store potential energy within their chemical bonds, making them vital for energy use in the body. The most immediate source of energy for skeletal muscle contraction is adenosine triphosphate (ATP), known as the universal energy donor. ATP can be broken down when energy is needed for cellular activities. ATP’s middle-range energy potential allows other molecules to donate energy to create ATP from adenosine diphosphate (ADP) and inorganic phosphate (Pi). ATP consists of an adenine molecule combined with a ribose (sugar) and three linked phosphates.
When ATP is combined with water (hydrolysis) and acted upon by the enzyme ATPase, the last phosphate group is cleaved, releasing approximately 7.3 kcal per mole of ATP under standard conditions [2]. This process reduces ATP to ADP and Pi. To regenerate ATP, a phosphate group is added to ADP in a process called phosphorylation, which requires a considerable amount of energy. Some ATP is generated independently of oxygen availability through substrate-level phosphorylation, while other ATP-producing reactions occur with the aid of oxygen through oxidative phosphorylation. ATP must be continuously synthesized as it is only stored for about 10 seconds in the body, necessitating various metabolic pathways to synthesize ATP from other molecules.
Creatine phosphate (CrP), also known as phosphocreatine (PCr), is another high-energy phosphate molecule stored in muscles in small amounts and used to quickly generate ATP. Creatine phosphate is depleted in less than 15 seconds of exercise but is resynthesized and stored during rest and recovery.
Chapter Summary
In this chapter, we explored the fundamental principles of bioenergetics, emphasizing its critical role in understanding how energy flows through living organisms. We discussed the two primary laws of bioenergetics, which govern energy conversion and transfer, and highlighted the importance of cellular structures such as the cell membrane, nucleus, and mitochondria in energy production. We delved into the metabolic pathways that convert carbohydrates, fats, and proteins into usable energy, focusing on the processes of glycolysis, lipolysis, and gluconeogenesis. The chapter also covered the classification and function of enzymes, including the roles of kinases, dehydrogenases, oxidases, and isomerases, as well as the significance of coenzymes like NAD+and FAD in facilitating biochemical reactions.
Additionally, we examined the role of high-energy phosphate molecules, particularly ATP and creatine phosphate, in storing and transferring energy within cells. Understanding these concepts is essential for comprehending how the body generates and utilizes energy, especially during physical exercise. By integrating these principles, we gain a deeper insight into the intricate processes that sustain life and enable physical activity, providing a solid foundation for further study in bioenergetics and exercise physiology.
Scholarly Questions
What is a substrate?
List 6 characteristics of enzymes.
What are the 3 substrates we use for fuel?
Basic Terms to Know with this section: bioenergetics, glycogen, glucose, metabolism, metabolic pathway, oxidation, reduction, redox reactions, creatine kinase, ATPase, enzyme, co-enzyme, mitochondria, and substrate.
What is the difference between anabolism and catabolism?
Know the basic structure of a muscle cell. What is the cell membrane called? The fluid portion of the cell? Which organelle is the most energy made? Where is the genetic material (DNA) of the cell located?
Can you name some high energy phosphates? Where is the potential energy stored?
Name two co-enzymes. How are they different than enzymes? How do they assist enzymes in biochemical reactions?
What is the chemical formula for glucose?
Approximately how long can ATP be stored?
Describe the roles of kinases, dehydrogenases, oxidases, and isomerases in metabolic pathways.
Guyton AC, Hall JE. Textbook of medical physiology. 11th ed. Philadelphia, PA: Elsevier Saunders; 2006. ↵
Powers SK, Howley ET. Exercise physiology (theory and application to fitness and performance). 9th Edition ed. New York, NY: McGraw-Hill; 2015. ↵
Guyton AC, Hall JE. Textbook of medical physiology. 11th ed. Philadelphia, PA: Elsevier Saunders; 2006. ↵
Kenney LK, Wilmore JH, Costil DL. Physiology of sport and exercise. In. Champaign, IL: Human Kinetics; 2012. ↵
McArdle WD, Katch FI, Katch VL. Exercise physiology: Nutrition, energy, and human performance. In. Exercise physiology: Nutrition, energy, and human performance: LWW; 2014, p 1088. ↵
McArdle WD, Katch FI, Katch VL. Exercise physiology: Nutrition, energy, and human performance. In. Exercise physiology: Nutrition, energy, and human performance: LWW; 2014, p 1088. ↵
Powers SK, Howley ET. Exercise physiology (theory and application to fitness and performance). 9th Edition ed. New York, NY: McGraw-Hill; 2015. ↵
Powers SK, Howley ET. Exercise physiology (theory and application to fitness and performance). 9th Edition ed. New York, NY: McGraw-Hill; 2015. ↵
Powers SK, Howley ET. Exercise physiology (theory and application to fitness and performance). 9th Edition ed. New York, NY: McGraw-Hill; 2015. ↵
definition
The study of how energy flows through living systems, particularly how organisms acquire, convert, store, and use energy to perform biological work.
The sum of all chemical reactions that occur within a living organism to maintain life.
A measure of disorder or randomness in a system. In thermodynamics and biology, it reflects how energy is distributed and how much of it is available to do useful work.
The amount of energy in a system that is available to do useful work. The most commonly used form is Gibbs Free Energy (G), defined by the equation: ΔG=ΔH−TΔS
Where:
ΔG = change in free energy
ΔH = change in enthalpy (total energy)
T = temperature in Kelvin
ΔS = change in entropy (disorder)
Chemical reactions that release free energy into the surroundings.
Chemical reactions that require an input of free energy to proceed.
Pairs of chemical reactions that occur together, where one reaction releases energy (exergonic) and the other requires energy (endergonic).
Reactions (redox) that involve the transfer of electrons between substances.
The cell membrane that surrounds a muscle fiber (muscle cell).
The cytoplasm of a muscle fiber (muscle cell). It is the gel-like substance that fills the space between the sarcolemma (muscle cell membrane) and the myofibrils (contractile structures).
Membrane-bound organelles found in most eukaryotic cells, often referred to as the "powerhouses of the cell" because they produce the majority of the cell’s usable energy in the form of ATP (adenosine triphosphate).
A globular protein that plays a central role in the structure and function of muscle cells and many other types of cells.
A motor protein that plays a central role in muscle contraction and various types of cell movement.
The breakdown of molecules to release energy.
The synthesis of complex molecules from simpler ones, which requires energy.
A substrate is the specific reactant that an enzyme acts upon during a chemical reaction.
Organic molecules composed of carbon (C), hydrogen (H), and oxygen (O), typically in a ratio close to 1:2:1. They are one of the main classes of biomolecules and serve as a primary source of energy for living organisms.
Large, complex biomolecules made up of chains of amino acids linked by peptide bonds.
A type of lipid, a class of hydrophobic (water-insoluble) molecules primarily composed of carbon (C), hydrogen (H), and a small amount of oxygen (O). They serve as a major source of long-term energy storage, provide insulation and protection for organs, and are essential components of cell membranes.
A series of interconnected biochemical reactions within a cell, where the product of one reaction serves as the substrate for the next.
Simple sugars (e.g., glucose, fructose).
Two monosaccharides linked together (e.g., sucrose, lactose).
Long chains of monosaccharides (e.g., starch, glycogen, cellulose).
A simple sugar (monosaccharide) with the molecular formula C₆H₁₂O₆.
The primary storage form of glucose in animals and humans, mainly found in the liver (for maintaining blood glucose levels) and skeletal muscles (for energy during activity).
A simple sugar (monosaccharide) with the molecular formula C₆H₁₂O₆, like glucose, but with a different structural arrangement.
A disaccharide of glucose and fructose.
The most common type of fat (lipid) found in the body and in food. They are composed of one glycerol molecule bonded to three fatty acids through ester bonds. Triglycerides serve as a major form of long-term energy storage, provide insulation, and protect organs.
A carboxylic acid with a long hydrocarbon chain, which can be either saturated (no double bonds) or unsaturated (one or more double bonds). Fatty acids are the building blocks of many lipids, including triglycerides and phospholipids, and play a critical role in energy storage, membrane structure, and signaling.
The metabolic process by which triglycerides (stored fats) are broken down into glycerol and free fatty acids. This occurs primarily in adipose tissue and is triggered when the body needs energy, such as during fasting, exercise, or low-carbohydrate intake.
A class of lipids that are major components of cell membranes. They are amphipathic molecules, meaning they have both water-loving (hydrophilic) and water-fearing (hydrophobic) components.
A class of lipids characterized by a core structure of four fused carbon rings (three six-membered rings and one five-membered ring). Unlike triglycerides, steroids are not composed of fatty acids and glycerol, but they are still classified as lipids because they are hydrophobic and insoluble in water.
Organic molecules that serve as the building blocks of proteins.
Biological catalysts, typically proteins (and sometimes RNA molecules called ribozymes), that speed up chemical reactions in living organisms without being consumed in the process.
Enzymes whose activity is regulated by the binding of molecules (called effectors or modulators) at a site other than the active site, known as the allosteric site. This binding causes a conformational change in the enzyme, which can either increase (activation) or decrease (inhibition) its catalytic activity.
Small, organic, non-protein molecules that assist enzymes in catalyzing biochemical reactions.
A coenzyme found in all living cells that plays a critical role in redox reactions.
A redox-active coenzyme derived from riboflavin (vitamin B₂).
Molecules that store and transfer energy within cells through phosphate bonds that release a large amount of free energy when hydrolyzed.
The primary energy carrier in all living organisms. It is a nucleotide composed of: adenine (a nitrogenous base), ribose (a five-carbon sugar), and three phosphate groups linked by high-energy bonds.
A nucleotide composed of: adenine (a nitrogenous base), ribose (a five-carbon sugar), and two phosphate groups.
A free phosphate ion (PO₄³⁻) that is not bound to an organic molecule.
An enzyme that catalyzes the hydrolysis of ATP (adenosine triphosphate) into ADP (adenosine diphosphate) and inorganic phosphate (Pi), releasing energy that can be used to power various cellular processes.
Also called phosphocreatine, it is a high-energy compound found primarily in muscle cells. It serves as a rapid energy reserve for the regeneration of ATP (adenosine triphosphate) during short bursts of intense activity, such as sprinting or heavy lifting.
