CARBOHYDRATES

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)

Glucose = Aldose

1

23

4

5

6

1

2

34

5

6

=Ketose

Structuralformula

Abbreviatedstructure

Simplifiedstructure

GalactoseGlucose

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

Glucose Glucose

Maltose

Fig. 5-5

(b) Dehydration reaction in the synthesis of sucrose

Glucose Fructose Sucrose

MaltoseGlucoseGlucose

(a) Dehydration reaction in the synthesis of maltose

1–4glycosidic

linkage

1–2glycosidic

linkage

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

All composed of glucoses

Starch granules inpotato tuber cells

Glycogengranulesin muscletissue

Cellulose fibrils ina plant cell wall

Cellulosemolecules

Glucosemonomer

GLYCOGEN

CELLULOSE

Hydrogen bonds

STARCH

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…

What’s in spit?