Adenosine triphosphate energy carrier

The initial conversion of light into chemical energy takes place in the thylakoid membrane. Besides the chlorophylls and series of electron carriers, the thylakoid membrane also contains the enzyme adenosine triphosphate (ATP) synthase. The enzymes that are responsible for the actual fixation of C02 and the synthesis of carbohydrate reside in the stroma that surround the thylakoid membrane. The stroma also contains deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and ribosomes that are essential for protein synthesis [37]. 

Since active transport often requires energy in the form of adenosine triphosphate (ATP), compounds or conditions that inhibit energy production (e.g., iodoac-etate, fluoride, cyanide, anaerobiosis) will impair active transport. The transport of a given compound also can be inhibited competitively by the coadministration of other compounds of sufficient structural similarity that they can compete with the first substance for sites on the carrier protein. 

In all organisms the free energy released in redox reactions is conserved in the energy-carrier molecule adenosine triphosphate (ATP) which is the universal carrier... 

Expenditure of energy. The term active transport implies that some energy must be used to fuel the carrier system. This energy is usually in the form of adenosine triphosphate (ATP) hydrolysis. 

Derivatives of phosphoric acid, pyrophosphoric acid, and related compounds are very important in biological systems. Pyrophosphoric acid is an anhydride of phosphoric acid. Adenosine triphosphate, an energy carrier that is universally found in living organisms, has a phosphorus dianhydride connected to an adenosine group by a phosphate ester linkage. Phosphorus ester bonds are used to form the polymeric backbone of DNA (see Chapter 27). 

In addition to their role in the formation of DNA and RNA (see Section 27.2), nucleotides have other important biological functions. For example, adenosine triphosphate (ATP) is an important energy carrier in biochemical reactions, and nicotinamide adenine dinucleotide is a coenzyme that is often involved in biochemical oxidation-reduction reactions. 

Figure 1 An example of the way metallo-enzymes are under controlled formation through both controlled uptake (rejection) of a metal ion and controlled synthesis of all the proteins connected to its metabolism and functions. The example is that of iron. Iron is taken up via a molecular carrier by bacteria but by a carrier protein, transferrin, in higher organisms. Pumps transfer either free iron or transferrin into the cell where Fe + ions are reduced to Fe + ions. The Fe + ions form heme, aided by cobalamin (cobalt 2 controls) and a zinc enzyme for a-laevulinic acid (ALA) synthesis. Heme or free iron then goes into several metallo-enzymes. Free Fe + also forms a metallo-protein transcription factor, which sees to it that synthesis of all iron carriers, storage systems, metallo-proteins, and metallo-enzymes are in fixed amounts (homeostasis). There are also iron metallo-enzymes for protection including Fe SOD (superoxide dismutase). Adenosine triphosphate (ATP) and H+ gradients supply energy for all processes. See References 1 -3.

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+ (Section 9.4.2). 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 (Pj) or when ATP is hydrolyzed to adenosine monophosphate (AMP) and pyrophosphate... 

Compounds that serve as energy carriers for the chemotrophs, linking catabolic and biosynthetic phases of metabolism, are adenosine phosphate and reduced pyridine nucleotides (such as nicotinamide dinucleotide or NAD). The structure of adenosine triphosphate (ATP) is shown in Fig. 1. It contains two energy-rich bonds, which upon hydrolysis, yield nearly eight kcal/mole for each bond broken. ATP is thus reduced to the diphosphate (ADP) or the monophosphate (AMP) form. 

There is another pnrine derivative of crucial biochemical importance - adenosine triphosphate (ATP). This substance is a carrier of energy, for when a phosphate link is broken, a large amount of energy is released. Note some trivial nomenclature the moieties produced by linking one of the heterocyclic bases to a ribose or 2 -deoxyribose sugar, are known as nucleosides (e.g. adenosine, guanosine, cytidine, thymidine). A nncleotide is a 5 -phosphate (or di- or tri-phosphate) of a nucleoside - ATP is a nucleotide. 

Once dioxygen arrives at a cell it is reduced to water in order to yield the energy necessary to convert adenosine diphosphate (ADP) to adenosine triphosphate (ATP), the energy carrier for cell processes. This oxygen burning (8.1) is mediated in turn by a series of metalloenzymes, such as cytochrome oxidase, which contains one heme Fe and one Cu in the active site. 

Active transport involves a carrier protein but differs from diffusion in two important ways. Cellular energy in the form of ATP (adenosine triphosphate) is required to drive the process and transport goes against the concentration gradient. By such a mechanism, substances can be concentrated in certain parts of the body. Active transport mechanisms are particularly important in the transport of ions, nutrients and neurotransmitters and may be involved in the transport of some drugs. Many drugs have been developed that interfere with the active transport of neurotransmitters (see Chapter 3, page 44). 

At Sheffield Krebs embarked upon the work that would elucidate some of the complex reactions of cell metabolism (the processes that extract energy from food). This extraction of energy is achieved via a series of chemical transformations that remove energy-rich electrons fiom molecules obtained from food. These electrons pass along a chain of molecular carriers in a way that ultimately gives rise to water and adenosine triphosphate (ATP), which is the primary source of chemical energy that powers cellular activity. 

The essential elements of Table 2.1 meet these demands. In all cases they are components of the metabolic system in cell or of important final products for example, cellulose for the upright standing of the plant. The function as constituents of such compounds is clear for C, H, and O. These three elements are together components of nearly all organic compounds in the plant [only hydrocarbons (e.g., carotins) are free of O], and therefore they build up the planfs shape. A similarly clear situation holds true for N and P, both of which are constituents of the information carriers DNA and RNA. N is a component of their purine and pyrimidine bases, while phosphoric acid esters of D-ribose or 2-deoxy-D-ribose form the backbone of their nucleotide sequences. Moreover, P plays a very important role in energy metabolism, the key compounds being nucleotide phosphates (e.g., adenosine triphosphate, ATP) (see Scheme 2.1) and the homologous molecules... 

Adenosine 5 -triphosphate involved in energy transfer in biochemical reactions. Uridine, cytidine, guanosine, and thymine triphosphates are also common in biological systems. Nicotinamide adenine dinucleotide phosphate is also an important energy carrier. 

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