Glucose

Glucose (Glc), a cellular respiration in both prokaryotes and eukaryotes. The name comes from the Greek word glykys (γλυκύς), which means "sweet", plus the suffix "-ose" which denotes a sugar.

Two glycolysis.

Glucose is commonly available in the form of a white substance or as a solid crystal. It can also be commonly found as an aqueous solution.

Structure

Glucose (C₆H₁₂O₆) contains six pyran, the cyclic form of glucose is also referred to as glucopyranose. In this ring, each carbon is linked to a hydroxyl side group with the exception of the fifth atom, which links to a sixth carbon atom outside the ring, forming a CH₂OH group.

Isomers

Aldohexose sugars have 4 D-series.

An additional asymmetric center at C-1 (called the anomeric carbon atom) is created when glucose cyclizes and two ring structures, called Haworth projection or in the standard chair conformation, the designation α means that the hydroxyl group attached to C-1 is positioned trans to the -CH₂OH group at C-5, while β means it is cis. Another popular method of distinguishing α from β is by observing whether the C-1 hydroxyl is below or above the plane of the ring, respectively, but this method is an inaccurate definition and may fail if the glucose ring is drawn upside down or in an alternative chair conformation. The α and β forms interconvert over a timescale of hours in aqueous solution, to a final stable ratio of α:β 36:64, in a process called mutarotation.^[2]

Rotamers

Within the cyclic form of glucose, rotation may occur around the O6-C6-C5-O5 torsion angle, termed the ω-angle, to form three rotamer conformations as shown in the diagram below. Referring to the orientations of the ω-angle and the O6-C6-C5-C4 angle the three stable staggered rotamer conformations are termed gauche-gauche (gg), gauche-trans (gt) and trans-gauche (tg). For methyl α-D-glucopyranose at equilibrium the ratio of molecules in each rotamer conformation is reported as 57:38:5 gg:gt:tg.^[3] This tendency for the ω-angle to prefer to adopt a gauche conformation is attributed to the gauche effect.

Production

Natural

1. Glucose is one of the products of photosynthesis in plants and some prokaryotes.
2. In animals and fungi, glucose is the result of the breakdown of starch.
3. In animals, glucose is synthesized in the liver and kidneys from non-carbohydrate intermediates, such as pyruvate and gluconeogenesis.

Commercial

Glucose is produced commercially via the cornstarch (from maize) is used almost exclusively.

This enzymatic process has two stages. Over the course of 1-2 hours near 100 °C, enzymes hydrolyze starch into smaller carbohydrates containing on average 5-10 glucose units each. Some variations on this process briefly heat the starch mixture to 130 °C or hotter one or more times. This heat treatment improves the solubility of starch in water, but deactivates the enzyme, and fresh enzyme must be added to the mixture after each heating.

In the second step, known as "saccharification", the partially hydrolyzed starch is completely hydrolyzed to glucose using the glucoamylase enzyme from the fungus Aspergillus niger. Typical reaction conditions are crystallizations.

Function

We can speculate on the reasons why glucose, and not another monosaccharide such as fructose (Fru), is so widely used in evolution, the ecosystem, and metabolism. Glucose can form from glycosylation is often essential to their function.

As an energy source

Glucose is a ubiquitous fuel in biology. It is used as an energy source in most organisms, from bacteria to humans. Use of glucose may be by either ATP. The insulin reaction, and other mechanisms, regulate the concentration of glucose in the blood. A high fasting blood sugar level is an indication of prediabetic and diabetic conditions.

Glucose is a primary source of energy for the brain, and hence its availability influences psychological processes. When glucose is low, psychological processes requiring mental effort (e.g., self-control) are impaired.^[4][5][6]

Glucose in glycolysis

Use of glucose as an energy source in cells is via aerobic or anaerobic respiration. Both of these start with the early steps of the hexokinase to prepare it for later breakdown to provide energy.

The major reason for the immediate phosphorylation of glucose by a phosphate group so the glucose 6-phosphate cannot easily cross the cell membrane. Irreversible first steps of a metabolic pathway are common for regulatory purposes.

As a precursor

Glucose is critical in the production of vitamin C (ascorbic acid) production. It is modified for use in these processes by the glycolysis pathway.

Glucose is used as a precursor for the synthesis of several important substances. starch solution sucrose, another important disaccharide, glucose is joined to fructose. These synthesis processes also rely on the phosphorylation of glucose through the first step of glycolysis.

Sources and absorption

All major dietary carbohydrates contain glucose, either as their only building block, as in starch and glycogen, and to fat cells, where it can be used to power reactions which synthesize some fats. Glycogen is the body's auxiliary energy source, tapped and converted back into glucose when there is need for energy.

See also

• Blood glucose or Blood Sugar
• HbA1c
• DMF (potential glucose-based biofuel)
• Glycation
• Glycosylation
• Photosynthesis
• Fructose

References