1. Pathway
     Energy source    Cofactors    Substrates  

2. Functions
     Anabolic hormones    Photosynthetic carbohydrate synthesis    Amino acid biosynthesis    Glycogen storage    Gluconeogenesis  

3. Regulation

4. Etymology

5. References

Anabolism ({{IPAc-en|ə|ˈ|n|æ|b|ə|l|ɪ|s|m}}) is the set of metabolic pathways that construct molecules from smaller units.^[1] These reactions require energy, known also as an endergonic process.^[2] Anabolism is the building-up aspect of metabolism, whereas catabolism is the breaking-down aspect. Anabolism is usually synonymous with biosynthesis.

Pathway

Polymerization, an anabolic pathway used to build macromolecules such as nucleic acids, proteins, and polysaccharides, uses condensation reactions to join monomers.^[3] Macromolecules are created from smaller molecules using enzymes and cofactors.

Energy source

Anabolism is powered by catabolism, where large molecules are broken down into smaller parts and then used up in cellular respiration. Many anabolic processes are powered by the cleavage of adenosine triphosphate (ATP).^[4] Anabolism usually involves reduction and decreases entropy, making it unfavorable without energy input.^[5] The starting materials, called the precursor molecules, are joined together using the chemical energy made available from hydrolyzing ATP, reducing the cofactors NAD⁺, NADP⁺, and FAD, or performing other favorable side reactions.^[6] Occasionally it can also be driven by entropy without energy input, in cases like the formation of the phospholipid bilayer of a cell, where hydrophobic interactions aggregate the molecules.^[7]

Cofactors

The reducing agents NADH, NADPH, and FADH₂,^[8] as well as metal ions,^[3] act as cofactors at various steps in anabolic pathways. NADH, NADPH, and FADH₂ act as electron carriers, while charged metal ions within enzymes stabilize charged functional groups on substrates.

Substrates

Substrates for anabolism are mostly intermediates taken from catabolic pathways during periods of high energy charge in the cell.^[10]

Functions

Anabolic processes build organs and tissues. These processes produce growth and differentiation of cells and increase in body size, a process that involves synthesis of complex molecules. Examples of anabolic processes include the growth and mineralization of bone and increases in muscle mass.

Anabolic hormones

Endocrinologists have traditionally classified hormones as anabolic or catabolic, depending on which part of metabolism they stimulate. The classic anabolic hormones are the anabolic steroids, which stimulate protein synthesis and muscle growth, and insulin.

Photosynthetic carbohydrate synthesis

Amino acid biosynthesis

All amino acids are formed from intermediates in the catabolic processes of glycolysis, the citric acid cycle, or the pentose phosphate pathway. From glycolysis, glucose 6-phosphate is a precursor for histidine; 3-phosphoglycerate is a precursor for glycine and cysteine; phosphoenol pyruvate, combined with the 3-phosphoglycerate-derivative erythrose 4-phosphate, forms tryptophan, phenylalanine, and tyrosine; and pyruvate is a precursor for alanine, valine, leucine, and isoleucine. From the citric acid cycle, α-ketoglutarate is converted into glutamate and subsequently glutamine, proline, and arginine; and oxaloacetate is converted into aspartate and subsequently asparagine, methionine, threonine, and lysine.^[10]

Glycogen storage

During periods of high blood sugar, glucose 6-phosphate from glycolysis is diverted to the glycogen-storing pathway. It is changed to glucose-1-phosphate by phosphoglucomutase and then to UDP-glucose by UTP--glucose-1-phosphate uridylyltransferase. Glycogen synthase adds this UDP-glucose to a glycogen chain.^[10]

Gluconeogenesis

Regulation

Anabolism operates with separate enzymes from catalysis, which undergo irreversible steps at some point in their pathways. This allows the cell to regulate the rate of production and prevent an infinite loop, also known as a futile cycle, from forming with catabolism.^[10]

The balance between anabolism and catabolism is sensitive to ADP and ATP, otherwise known as the energy charge of the cell. High amounts of ATP cause cells to favor the anabolic pathway and slow catabolic activity, while excess ADP slows anabolism and favors catabolism.^[10] These pathways are also regulated by circadian rhythms, with processes such as glycolysis fluctuating to match an animal's normal periods of activity throughout the day.^[11]

Etymology

The word anabolism is from New Latin, which got the roots from {{lang-grc-gre|ἁνά}}, "upward" and {{lang|grc|βάλλειν}}, "to throw".

References

• Sammanthurai
• Sammanthurai Divisional Secretary's Division
• Sammanthurai Electoral District
• Sam Marata
• Sam Marcy
• Sam Marin
• Sammarinese Air Force
• Sammarinese-American
• Sammarinese Americans
• Sammarinese-Americans
• Sammarinese Citizenry Meeting, 1906
• Sammarinese Democratic Party
• Sammarinese Democratic Union
• Sammarinese Democrats
• Sammarinese Fascism
• Sammarinese land ownership referendum, 2011
• Sammarinese National Olympic Committee
• Sammarinese people
• Sammarinese people (disambiguation)
• Sammarinese People's Party
• Sammarinese political reform referendum, 1906
• Sammarinese referenda, 2013
• Sammarinese registration plates
• Sammarinese women
• Sam Marklund