Encyclopedia of Biology

from carbohydrates but from fats and protein as well.
Glucose is known as a dextrorotatory sugar (a chiral
molecule that rotates plane-polarized light to the right),
which is sweet, colorless, and soluble.

glycocalyx A thick, (7.5–200 nm) extracellular,
sticky coating of oligosaccharides linked to plasma
membrane glycoprotein and glycolipids; found around
the outside of eukaryote cells, and used to adhere to
surfaces. Also called the cell coat.

glycogen A large polysaccharide; stored energy
found in the muscles and liver. It consists of many
monosaccharide glucose molecules linked together and

is used as a fuel during exercise, broken down as need-

ed; glycogen is the primary storage form of glucose in

animals. Also known as stored sugar or animal starch.

glycolysis The anaerobic pathway or enzymatic conver-

sion (using 11 different enzymes) in the cell’s cytoplasm of

glucose to simpler compounds. Glucose, a six-carbon

sugar, is converted into two molecules of pyruvic acid of

three carbons each, with two molecules of NADH and

two ATPs as by-products. It is the most universal and

basic energy harvesting system; it transforms glucose into

lactic acid in muscles and other tissues for energy produc-

tion when there is not enough oxygen available.

In aerobic respiration, the two pyruvic acids are

further used in the KREBS CYCLE.

glycolysis 149

(starch, glycogen) (glucose)

ATP

ATP

ADP

ADP

2 NAD +

2 NADH

2 ADP

2 ADP

2 ATP

2 ATP

(glucose 1-phosphate)

(glucose 6-phosphate)

fructose 6-phosphate

fructose 1,6-diphosphate

2 x (glyceraldehyde

3-phosphate)

2 x (1,3-diphosphoglycerate)

2 x (3-phosphoglycerate)

2 x (2-phosphoglycerate)

2 x (phosphoenolpyruvate)

2 x (pyruvate)

This stage requires energy

and the conversion of ATP

to ADP

Production of fructose

diphosphate

The 6C fructose diphosphate

breaks into two 3C molecules

This stage yields energy and

2 molecules of pyruvate

ADP is converted to ATP.

NADH is also formed, and

may participate in subsequent

reactions

The anaerobic pathway or enzymatic conversion (using 11 different enzymes) in the cell’s cytoplasm of glucose to simpler compounds.