Download 04 Carbohydrates Note

Carbohydrates
 An immense variety of polymers can be built from a small set of
monomers.
Carbohydrates
 Organic molecules made of sugars (carbon, hydrogen and
oxygen) and their polymers
 Classified by the type and number of simple sugars
 major source of ENERGY and CARBON!
1. Monosaccharides
 simple sugars in which C, H, and O occur in ratio = CxH2xOx
 major nutrients for cells; glucose is most common
 can be produced by photosynthetic organisms from CO2, H2O,
sunlight
 store energy in chemical bonds, which is released during
cellular respiration
Characteristics of a sugar:
 An OH-group attached to each carbon except one, which
double bonded to an oxygen (carbonyl)
 Size of carbon skeleton – commonly 3 (triose), 5 (pentose),
and 6 (hexose)
 In aqueous solutions, many simple sugars form rings
a) Glucose C6H12O6 (two forms)
b) Galactose
 Enantiomer (mirror image) of glucose
 found in milk and yoghurt
 glucose + galactose = lactose
c) Fructose
 fruit sugar
 fructose + glucose = sucrose (yummy)
2. Disaccharides
 “double” sugar that consists of 2 monosaccharides joined
by a glycosidic linkage
 glycosidic linkage = covalent bond formed by condensation
reaction between two sugar monomers, for example,
maltose.
a)
Maltose C12H22O11
α glucose + α glucose  maltose + H2O
(C6H12O6) (C6H12O6) (C12H22O11) (H2O)
Disaccharide
Monomers
General Comments
Maltose
α-glucose + α-glucose
Important in brewing beer
Lactose
α-glucose + galactose
Present in milk
Sucrose
α-glucose + fructose
Table sugar; most
common disaccharide;
transport form in plants
 NOTE: Disaccharides can be broken down into simple
sugars again through a hydrolysis reaction
3. Polysaccharides
 “many” sugars
 complex carbohydrates composed of many simple sugars
(1000’s) synthesized by condensation rxns
 have storage and structural roles
 connected via alpha (α) or beta (β) glycosidic linkages
Energy Storage polysaccharides:
a) Starch
 1000’s of units of α glucose; helical; α 1-4
linkages
 the main storage product in most plants
 when energy is needed, the enzyme amylase
assists in the breakdown
 made of 2 types of polysaccharides:
Amylopectin
Amylose
(p.31)
(branched)
(unbranched)
b) Glycogen (p.32)
 the polysaccharide that vertebrates use to
store glucose (in muscle and liver tissue)
 lots of branching (α 1-4 and α 1-6 links) of
α-glucose units
Structural polysaccharides:
a) Cellulose (p.33)
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b) Chintin (p.33)
an insoluble linear polysaccharide of Dglucose, used for support in plants
joined by β 1-4 linkages
its bonds are resistant to hydrolysis
important in our diet as fiber
 Cellulose like polymer used in the
exoskeletons of bugs and lobsters and the
cell wall of some fungi
 Monomer = “amino sugar “Nacetylglucosamine (glucose with a nitrogen
group)