Anabolism () is the set of metabolic pathways that construct like DNA or RNA from smaller units.
Pathway
Polymerization, an anabolic pathway used to build macromolecules such as nucleic acids, proteins, and polysaccharides, uses condensation reactions to join monomers.
[ Alt URL] 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
ATP hydrolysis.
Anabolism usually involves
Redox and decreases
entropy, making it unfavorable without energy input.
The starting materials, called the precursor molecules, are joined using the
chemical energy made available from hydrolyzing ATP, reducing the cofactors NAD
+, NADP
+, and FAD, or performing other favorable side reactions.
Occasionally it can also be driven by
entropy without energy input, in cases like the formation of the
Lipid bilayer of a cell, where hydrophobic interactions aggregate the molecules.
Cofactors
The reducing agents NADH, NADPH, and FADH
2,
as well as metal ions,
act as cofactors at various steps in anabolic pathways. NADH, NADPH, and FADH
2 act as
, while charged metal ions within enzymes stabilize charged
on substrates.
Substrates
Substrates for anabolism are mostly intermediates taken from catabolic pathways during periods of high
energy charge in the cell.
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
. Examples of anabolic processes include the growth and mineralization of
bone and increases in
muscle mass.
Anabolic hormones
have traditionally classified
as anabolic or catabolic, depending on which part of metabolism they stimulate. The classic anabolic hormones are the
, which stimulate protein synthesis and muscle growth, and
insulin.
Photosynthetic carbohydrate synthesis
Photosynthesis in plants and certain bacteria is an anabolic process that produces
glucose,
cellulose,
starch,
, and
from CO
2.
It uses the energy produced from the light-driven reactions of photosynthesis, and creates the precursors to these large molecules via
Carbon fixation in the photosynthetic carbon reduction cycle, a.k.a. the Calvin cycle.
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
Pyruvic acid is a precursor for
alanine,
valine,
leucine, and
isoleucine. From the citric acid cycle, α-ketoglutarate is converted into
Glutamic acid and subsequently
glutamine,
proline, and
arginine; and
Oxaloacetic acid is converted into
Aspartic acid and subsequently
asparagine,
methionine,
threonine, and
lysine.
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.
Gluconeogenesis
Glucagon is traditionally a catabolic hormone, but also stimulates the anabolic process of
gluconeogenesis by the liver, and to a lesser extent the kidney cortex and intestines, during starvation to prevent
hypoglycemia.
It is the process of converting pyruvate into glucose. Pyruvate can come from the breakdown of glucose,
lactic acid, amino acids, or
glycerol.
The gluconeogenesis pathway has many reversible enzymatic processes in common with glycolysis, but it is not the process of glycolysis in reverse. It uses different irreversible enzymes to ensure the overall pathway runs in one direction only.
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.
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.
Etymology
The word
anabolism is from
Neo-Latin, with roots from , "upward" and βάλλειν, "to throw".
