Oligosacáridos Son carbohidratos que provienen de la unión de algunos monosacáridos; se considera en este grupo a los carbohidratos que tienen de dos a diez monosacáridos.

Los disacáridos Resultan de la unión de dos monosacáridos mediante un enlace glucosídico como la sacarosa o “azúcar de caña”, formada por glucosa y fructosa, que es muy utilizada en la alimentación humana, y la lactosa o “azúcar de la leche” que se forma con los monosacáridos: glucosa y galactosa.

SACAROSA LACTOSA

La unión o enlace glucosídico La unión o enlace glucosídico entre dos monosacáridos se realiza con el desprendimiento de una molécula de agua.

La sacarosa (C12H22O11) Procede de la unión de una molécula de glucosa y una de fructosa con la eliminación de una molécula de agua entre ellas.

Polisacáridos Se forman con la unión de muchos monosacáridos, sobre todo glucosas en forma lineal o ramificada. Algunos llegan a tener varios miles de unidades, principalmente de glucosa, como sucede con la celulosa, que tiene un peso molecular muy elevado.

FIGURE 3-9a Cellulose structure and function Cellulose can be incredibly tough. (a) Wood in this 3000-year-old bristlecone pine is primarily cellulose.

FIGURE 3-9 Cellulose structure and function Cellulose can be incredibly tough. (b) Cellulose forms the cell wall that surrounds each plant cell.

FIGURE 3-9 Cellulose structure and function Cellulose can be incredibly tough. (c) Plant cell walls often consist of cellulose fibers in layers that run at angles to each other and resist tearing in both directions.

FIGURE 3-9 Cellulose structure and function Cellulose can be incredibly tough. (d) Cellulose is composed of glucose subunits. Compare this structure with Fig. 3-8c and notice that every other glucose molecule in cellulose is "upside down."

Los polisacáridos son insolubles en agua pero algunos, como el almidón, con agua caliente forman una solución coloidal conocida como “engrudo”

El almidón es un polímero de la glucosa, formado por varias cadenas de varios cientos de unidades de glucosa.

FIGURE 3-8 (part 1) Starch is an energy-storage polysaccharide made of glucose subunits (a) Starch globules inside individual potato cells. Most plants synthesize starch, which forms water-insoluble globules consisting of many starch molecules. (b) A small section of a single starch molecule, which occurs as branched chains of up to half a million glucose subunits. (c) The precise structure of the blue highlighted portion of the starch molecule in (b). Notice the linkage between the individual glucose subunits for comparison with cellulose (see Fig. 3-9).

FIGURE 3-8 (part 2) Starch is an energy-storage polysaccharide made of glucose subunits (a) Starch globules inside individual potato cells. Most plants synthesize starch, which forms water-insoluble globules consisting of many starch molecules. (b) A small section of a single starch molecule, which occurs as branched chains of up to half a million glucose subunits. (c) The precise structure of the blue highlighted portion of the starch molecule in (b). Notice the linkage between the individual glucose subunits for comparison with cellulose (see Fig. 3-9).

Otros polisacáridos importantes son: El glucógeno o “almidón animal”

La Quitina FIGURE 3-10 Chitin: A unique polysaccharide Chitin has the same bonding configuration of glucose molecules as cellulose does. In chitin, however, the glucose subunits have a nitrogen-containing functional group (yellow) instead of a hydroxyl group. Tough, flexible chitin supports the otherwise soft bodies of arthropods (insects, spiders, and their relatives) and certain fungi, such as this mushroom.

FIGURE 3-10 (part 1) Chitin: A unique polysaccharide Chitin has the same bonding configuration of glucose molecules as cellulose does. In chitin, however, the glucose subunits have a nitrogen-containing functional group (yellow) instead of a hydroxyl group. Tough, flexible chitin supports the otherwise soft bodies of arthropods (insects, spiders, and their relatives) and certain fungi, such as this mushroom.

FIGURE 3-10 (part 2) Chitin: A unique polysaccharide Chitin has the same bonding configuration of glucose molecules as cellulose does. In chitin, however, the glucose subunits have a nitrogen-containing functional group (yellow) instead of a hydroxyl group. Tough, flexible chitin supports the otherwise soft bodies of arthropods (insects, spiders, and their relatives) and certain fungi, such as this mushroom.

Los mucopolisacáridos