Carbohydrates • Important energy source for cell • Monosaccharides – monomers for sugars • Disaccharides – 2 sugars linked by glycosidic covalent bond • Polysaccharide – many sugars (100-1000’s) • All sugars have a C1H2O1 formula.
Monomers: Monosaccharides • Glucose • Fructose • Galactose
Glucose (an aldose) Fructose (a ketose)
6 5 1 4 2 3 Glucose = Aldose
6 5 2 1 3 4 =Ketose
Simplified structure Abbreviated structure Structural formula
2 forms of glucose Alpha-Glucose Beta-Glucose
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.
Alpha-Glucose Starch: Alpha-glucose is the monomer unit in starch.
As a result of the bond angles in the alpha acetal linkage, starch (amylose) actually forms a spiral structure.
Beta-Glucose • Cellulose: Beta glucose is the monomer unit in cellulose.
As a result of the bond angles in the beta acetal linkage, cellulose is mostly a linear chain.
Disaccharides • Lactose • Maltose • Sucrose
Disaccharides • Two monosaccharides (monomers) can bond to form a disaccharide in a dehydration reaction • An example is a glucose monomer bonding to a fructose monomer to form sucrose, a common disaccharide
Glucose Glucose Maltose
Fig. 5-5 1–4 glycosidic linkage Glucose Glucose Maltose (a) Dehydration reaction in the synthesis of maltose 1–2 glycosidic linkage Glucose Fructose Sucrose (b) Dehydration reaction in the synthesis of sucrose
Polysaccharides • Polysaccharides are polymers of monosaccharides (long chains of sugar) • They can function in the cell as a storage molecule or as a structural compound
Polysaccharide • Starch – plant energy storage • Glycogen- animal energy storage • Cellulose- cell wall of plants • Chitin – cell wall of fungi
STARCH Glucose monomer Starch granules in potato tuber cells Glycogen granules in muscle tissue GLYCOGEN CELLULOSE Cellulose fibrils in a plant cell wall Hydrogen bonds Cellulose molecules
Polysaccharides • Polysaccharides are hydrophilic (water-loving) • Cotton fibers, such as those in bath towels, are water absorbent
To get to the energy, you must break the bonds connecting the glucoses. But those starch bonds are very hard to break…