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The overall reaction can be expressed this way: [10] Glucose + 2 NAD + + 2 P i + 2 ADP → 2 pyruvate + 2 NADH + 2 ATP + 2 H + + 2 H 2 O + energy. Starting with glucose, 1 ATP is used to donate a phosphate to glucose to produce glucose 6-phosphate. Glycogen can be converted into glucose 6-phosphate as well with the help of glycogen phosphorylase.
Once glucose enters the cell, the first step is phosphorylation of glucose by a family of enzymes called hexokinases to form glucose 6-phosphate (G6P). This reaction consumes ATP, but it acts to keep the glucose concentration inside the cell low, promoting continuous transport of blood glucose into the cell through the plasma membrane transporters.
Fermentation is another process by which cells can extract energy from glucose. It is not a form of cellular respiration, but it does generate ATP, break down glucose, and produce waste products. Fermentation, like aerobic respiration, begins by breaking glucose into two pyruvate molecules.
The brain also uses glucose during starvation, but most of the body's glucose is allocated to the skeletal muscles and red blood cells. The cost of the brain using too much glucose is muscle loss. If the brain and muscles relied entirely on glucose, the body would lose 50% of its nitrogen content in 8–10 days. [13]
The d-isomer, d-glucose, also known as dextrose, occurs widely in nature, but the l-isomer, l-glucose, does not. Glucose can be obtained by hydrolysis of carbohydrates such as milk sugar , cane sugar (sucrose), maltose, cellulose, glycogen, etc. Dextrose is commonly commercially manufactured from starches, such as corn starch in the US and ...
The cells will use glucose for energy as normal, and any glucose not used for energy will enter the polyol pathway. When blood glucose is normal (about 100 mg/dL or 5.5 mmol/L), this interchange causes no problems, as aldose reductase has a low affinity for glucose at normal concentrations. [citation needed]
Mechanisms 1 and 2 represent hydride gain, in which the molecule gains what amounts to be one hydride ion. Mechanisms 3 and 4 radical formation and hydride loss. Radical species contain unpaired electron atoms and are very chemically active. Hydride loss is the inverse process of the hydride gain seen before.
In this diagram, the hydride acceptor C4 carbon is shown at the top. When the nicotinamide ring lies in the plane of the page with the carboxy-amide to the right, as shown, the hydride donor lies either "above" or "below" the plane of the page. If "above" hydride transfer is class A, if "below" hydride transfer is class B. [56]