MEDICAL BIOLOGY, ANATOMY, HUMAN PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

BIOLOGY

CHAPTER 1. BIOLOGICAL FOUNDATIONS OF HUMAN VITAL ACTIVITY

1.3. MOLECULAR-GENETIC AND CELLULAR LEVELS OF LIFE ORGANIZATION

1.3.2. Structural, chemical and functional organization of eukaryotic cells

Cellular Energy Supply: ATP, Oxidative Phosphorylation, Energy Distribution

ATP (adenosine triphosphate) is a universal energy supplier for all endergonic processes within The Cell. Chemically, ATP is a nucleotide composed of adenine, ribose, and three phosphoric acid residues; it contains two high-energy phosphoanhydride bonds (high-energy bonds). During metabolic reactions, under the action of Enzymes, ATP readily loses one or two phosphoric acid residues, yielding adenosine diphosphate (ADP) or adenosine monophosphate (AMP), respectively, and releasing energy at a rate of 42 kJ per phosphate residue. Conversely, the attachment of phosphate residues to AMP or ADP is accompanied by the storage of energy in the newly formed ATP molecule.

The pathways of ATP generation in the cell include Glycolysis and oxidative phosphorylation. Glycolysis is The process of glucose breakdown that takes place in the cell Cytosol. During this process, the six-carbon glucose molecule C₆H₁₂O₆ is split into two three-carbon molecules of pyruvic or lactic acid. Glycolysis is a type of Fermentation used to meet energy demands in the form of ATP by most anaerobic organisms on Earth, as well as by aerobes under conditions of insufficient molecular oxygen supply. In humans and animals, a distinction is made between aerobic glycolysis, which results in The formation of two molecules of pyruvic acid (Pyruvate) C3H4O3 from a single glucose molecule, and anaerobic glycolysis, which yields two molecules of lactic acid (lactate) C₃H₆O₃. Aerobic glycolysis is also viewed as an intermediate stage in the aerobic oxidation of glucose down to its final products — CO₂ and Water. As a result of The breakdown of a single glucose molecule via aerobic or anaerobic glycolysis, the net yield of ATP is two molecules:

Class="center">

The glycolysis process has low efficiency. This is because the End products of glycolysis still contain a considerable amount of bound energy. The primary role in supplying Cells with energy in the form of ATP is played by oxidative phosphorylation. In this case, ATP synthesis occurs within the Mitochondria. Aerobic Respiration and oxidative phosphorylation take place on The inner mitochondrial membranes. Oxygen-based respiration (Biological Oxidation) extracts energy from Organic compounds. This system is organized as an Electron Transport Chain, or the mitochondrial Respiratory Chain. Oxidative phosphorylation is the process by which the chemical energy released during Electron transport along the mitochondrial respiratory chain is captured and utilized to synthesize adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate (P_i). The synthesis of ATP from ADP and inorganic phosphate occurring in mitochondria is known as the coupling of respiration and oxidative phosphorylation. As a result of oxidative phosphorylation, 36 molecules of ATP are formed:

The overall equation for the aerobic oxidation of glucose, which accounts for the ATP generated through both glycolysis and oxidative phosphorylation, is as follows:

The energy stored within the high-energy bonds of ATP becomes available for use across all cellular life processes. ATP serves as a universal energy accumulator.