Kamis, 19 November 2015
Energy in living organisme cell
Cells Transform Different Types of Energy
Living organisms require a continual input of free energy for three major purposes: (1) the performance of mechanical work in muscle contraction and other cellular movements, (2) the active transport of molecules and ions, and (3) the synthesis of macromolecules and other biomolecules from simple precursors. The free energy used in these processes, which maintain an organism in a state that is far from equilibrium, is derived from the environment.
The First Law of Thermodynamics states that energy can be neither created nor destroyed. The amount of energy in the universe is constant. Nevertheless, energy can be converted from one form into another. Photosynthetic organisms, or phototrophs, use the energy of sunlight to convert simple energy-poor molecules into morecomplex energy-rich molecules that serve as fuels. In other words, photosynthetic organisms transform light energy into chemical energy. Indeed, this transformation is ultimately the primary source of chemical energy for the vast majority of organisms, human beings included. Chemotrophs, which include animals, obtain chemical energy through the oxidation
of foodstuffs generated by phototrophs. Chemical energy obtained from the oxidation of carbon compounds may be transformed into the unequal distribution of ions across a membrane, resulting in an ion gradient. This gradient, in turn, is an energy source that can be used to move molecules across membranes, that can be converted into yet other types of chemical energy, or that can convey
information in the form of nerve impulses. In addition, chemical energy can be transduced into mechanical energy. We convert the chemical energy of a fuel into structural alterations of contractile proteins that result in muscle contraction and movement. Finally, chemical energy powers the reactions that result in the synthesis of biomolecules.At any given instant in a cell, thousands of energy transformations are taking place. Energy is being extracted from fuels and used to power biosynthetic processes. These transformations are referred to as metabolismor intermediary
metabolism. (P:569)
ATP Is the Universal Currency of Free Energy in Biological Systems
Just as commerce is facilitated by the use of a common currency, the commerce of the cell metabolism is facilitated by the use of a common energy currency, adenosine triphosphate(ATP). Part of the free energy derived from the oxidation of foodstuffs and from light is transformed into this highly accessible molecule, which acts as the free-energy donor in most energy-requiring processes such as motion, active transport, or biosynthesis. ATP is a nucleotide consisting of an adenine, a ribose, and a triphosphate unit (Figure 14.3). The active form of ATP is usually a complex of ATP with Mg2+ or Mn2+. In considering the role of ATP as an energy carrier, we can focus on its triphosphate moiety. ATP is an energy-rich molecule because its triphosphate unit contains two
phosphoanhydride bonds. A large amount of free energy is liberated when ATP is hydrolyzed to adenosine diphosphate (ADP) and orthophosphate (Pi) or when ATP is hydrolyzed to adenosine monophosphate (AMP) and pyrophosphate (PPi).
The precise ∆G°for these reactions depends on the ionic strength of the medium and on the concentrations of Mg2+ and other metal ions. Under typical cellular concentrations, the actual ∆G for these hydrolyses is approximately -12 kcal mol-1 (-50 kJ mol-1).
The free energy liberated in the hydrolysis of ATP is harnessed to drive reactions that require an input of free energy, such as muscle contraction. In turn, ATP is formed from ADP and Pi when fuel molecules are oxidized in chemotrophs or when light is trapped by phototrophs. This ATP ADP cycle is the fundamental mode of energy exchange in biological systems. Some biosynthetic reactions are driven by hydrolysis of nucleoside triphosphates that are analogous to ATP namely, guanosine triphosphate (GTP), uridine triphosphate (UTP), and cytidine triphosphate (CTP). The diphosphate forms of these nucleotides are denoted by GDP, UDP, and CDP, and the monophosphate forms by GMP, UMP, and CMP.
Enzymes can catalyze the transfer of the terminal phosphoryl group from one nucleotide to another. The phosphorylation of nucleoside monophosphates is catalyzed by a family of nucleoside monophosphate kinases. The phosphorylation of nucleoside diphosphates is catalyzed by nucleoside diphosphate kinase, an enzyme with broad specificity. It is intriguing to note that, although all of the nucleotide triphosphates are energetically equivalent, ATP is nonetheless the primary cellular energy carrier. In addition, two important electron carriers, NAD+ and FAD, are derivatives of ATP. The role of ATP in energy metabolism is paramount. (P:572)
Berg, Tymoczko, Stryer.
Biochemistry, fifth edition
© W. H. Freeman and Company and Sumanas, Inc.
from: center library of Syarif Hidayatullah State Islamic University, Jakarta
Living organisms require a continual input of free energy for three major purposes: (1) the performance of mechanical work in muscle contraction and other cellular movements, (2) the active transport of molecules and ions, and (3) the synthesis of macromolecules and other biomolecules from simple precursors. The free energy used in these processes, which maintain an organism in a state that is far from equilibrium, is derived from the environment.
The First Law of Thermodynamics states that energy can be neither created nor destroyed. The amount of energy in the universe is constant. Nevertheless, energy can be converted from one form into another. Photosynthetic organisms, or phototrophs, use the energy of sunlight to convert simple energy-poor molecules into morecomplex energy-rich molecules that serve as fuels. In other words, photosynthetic organisms transform light energy into chemical energy. Indeed, this transformation is ultimately the primary source of chemical energy for the vast majority of organisms, human beings included. Chemotrophs, which include animals, obtain chemical energy through the oxidation
of foodstuffs generated by phototrophs. Chemical energy obtained from the oxidation of carbon compounds may be transformed into the unequal distribution of ions across a membrane, resulting in an ion gradient. This gradient, in turn, is an energy source that can be used to move molecules across membranes, that can be converted into yet other types of chemical energy, or that can convey
information in the form of nerve impulses. In addition, chemical energy can be transduced into mechanical energy. We convert the chemical energy of a fuel into structural alterations of contractile proteins that result in muscle contraction and movement. Finally, chemical energy powers the reactions that result in the synthesis of biomolecules.At any given instant in a cell, thousands of energy transformations are taking place. Energy is being extracted from fuels and used to power biosynthetic processes. These transformations are referred to as metabolismor intermediary
metabolism. (P:569)
ATP Is the Universal Currency of Free Energy in Biological Systems
Just as commerce is facilitated by the use of a common currency, the commerce of the cell metabolism is facilitated by the use of a common energy currency, adenosine triphosphate(ATP). Part of the free energy derived from the oxidation of foodstuffs and from light is transformed into this highly accessible molecule, which acts as the free-energy donor in most energy-requiring processes such as motion, active transport, or biosynthesis. ATP is a nucleotide consisting of an adenine, a ribose, and a triphosphate unit (Figure 14.3). The active form of ATP is usually a complex of ATP with Mg2+ or Mn2+. In considering the role of ATP as an energy carrier, we can focus on its triphosphate moiety. ATP is an energy-rich molecule because its triphosphate unit contains two
phosphoanhydride bonds. A large amount of free energy is liberated when ATP is hydrolyzed to adenosine diphosphate (ADP) and orthophosphate (Pi) or when ATP is hydrolyzed to adenosine monophosphate (AMP) and pyrophosphate (PPi).
The free energy liberated in the hydrolysis of ATP is harnessed to drive reactions that require an input of free energy, such as muscle contraction. In turn, ATP is formed from ADP and Pi when fuel molecules are oxidized in chemotrophs or when light is trapped by phototrophs. This ATP ADP cycle is the fundamental mode of energy exchange in biological systems. Some biosynthetic reactions are driven by hydrolysis of nucleoside triphosphates that are analogous to ATP namely, guanosine triphosphate (GTP), uridine triphosphate (UTP), and cytidine triphosphate (CTP). The diphosphate forms of these nucleotides are denoted by GDP, UDP, and CDP, and the monophosphate forms by GMP, UMP, and CMP.
Enzymes can catalyze the transfer of the terminal phosphoryl group from one nucleotide to another. The phosphorylation of nucleoside monophosphates is catalyzed by a family of nucleoside monophosphate kinases. The phosphorylation of nucleoside diphosphates is catalyzed by nucleoside diphosphate kinase, an enzyme with broad specificity. It is intriguing to note that, although all of the nucleotide triphosphates are energetically equivalent, ATP is nonetheless the primary cellular energy carrier. In addition, two important electron carriers, NAD+ and FAD, are derivatives of ATP. The role of ATP in energy metabolism is paramount. (P:572)
Berg, Tymoczko, Stryer.
Biochemistry, fifth edition
© W. H. Freeman and Company and Sumanas, Inc.
from: center library of Syarif Hidayatullah State Islamic University, Jakarta
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