Glucose Monomers
They differ only in the direction that -H and -OH groups point on carbon 1 (See the images to the right ). When alpha-glucose molecules are joined chemically to form a polymer, starch is formed. When beta-glucose molecules are joined to form a polymer, cellulose is formed.
They differ only in the direction that -H and -OH groups point on carbon 1 (See the images to the right ). When alpha-glucose molecules are joined chemically to form a polymer, starch is formed. When beta-glucose molecules are joined to form a polymer, cellulose is formed.
Sugar Polymers
Polysaccharides are carbohydrate polymers comprised of many (hundreds to thousands) monosaccharide monomers.
The type of polymer formed depends on the monosaccharide subunits involved and the bonding arrangement between them.
Three key polymers can be made from glucose monosaccharides – cellulose, starch (in plants) and glycogen (in animals).
Cellulose
Cellulose is a structural polysaccharide that is found in the cell wall of plants.
It is a linear molecule composed of β-glucose subunits (bound in a 1-4 arrangement).
Because it is composed of β-glucose, it is indigestible for most animals (lack the enzyme required to break it down)
Starch
Starch is an energy storage polysaccharide found in plants.
It is composed of α-glucose subunits (bound in a 1-4 arrangement) and exists in one of two forms – amylose or amylopectin.
Glycogen
Glycogen is an energy storage polysaccharide formed in the liver in animals.
It is composed of α-glucose subunits linked together by both 1-4 linkages and 1-6 linkages (branching).
Polysaccharides are carbohydrate polymers comprised of many (hundreds to thousands) monosaccharide monomers.
The type of polymer formed depends on the monosaccharide subunits involved and the bonding arrangement between them.
Three key polymers can be made from glucose monosaccharides – cellulose, starch (in plants) and glycogen (in animals).
Cellulose
Cellulose is a structural polysaccharide that is found in the cell wall of plants.
It is a linear molecule composed of β-glucose subunits (bound in a 1-4 arrangement).
Because it is composed of β-glucose, it is indigestible for most animals (lack the enzyme required to break it down)
- Ruminants (e.g. cows) may digest cellulose due to the presence of helpful bacteria in a specialised stomach
- Caecotrophs (e.g. rabbits) will re-ingest specialised faeces that contain digested cellulose (broken down in the caecum)
Starch
Starch is an energy storage polysaccharide found in plants.
It is composed of α-glucose subunits (bound in a 1-4 arrangement) and exists in one of two forms – amylose or amylopectin.
- Amylose is a linear (helical) molecule while amylopectin is branched (contains additional 1-6 linkages)
- Amylose is harder to digest and less soluble, however, as it takes up less space, is the preferred storage form in plants
Glycogen
Glycogen is an energy storage polysaccharide formed in the liver in animals.
It is composed of α-glucose subunits linked together by both 1-4 linkages and 1-6 linkages (branching).
- It is akin to amylopectin in plants, but is more highly branched (1-6 linkages occur every ~10 subunits as opposed to ~20)
Polysaccharides of Glucose
2.3 Carbohydrates
Skill:
2.3.S1 Use of molecular visualization software to compare cellulose, starch and glycogen.
2.3.S1 Use of molecular visualization software to compare cellulose, starch and glycogen.
Objectives:
- Demonstrate use of JMol to view molecular structures, including changing image size, rotating the image and changing the style of the molecular model.
- Identify carbon, hydrogen and oxygen atoms by color.
Molecular Structures of sugar polymers
* Click on the buttons to go to an external interactive jsmol website for each of the molecules.