3. They can be regarded as the complexes
of carbon and water.
Carbohydrate is a type of organic compounds
Containing carbon, hydrogen and oxygen.
Because the ratio of atoms number
of hydrogen and oxygen
Is the same as that in water molecule (2:1).
4. Some simple carbohydrate molecules
Can be the building blocks of the
More complicated ones.
Then, these building blocks are called
Monosaccharides
5. The carbon(in some exceptional cases) may carry-
• An aldehyde group
• A ketone group
If it carries an aldehyde group,
It is called an aldose.
If it carries a ketone group,
It is called a ketose.
8. Monosaccharides can also be classified
According to the amount of carbon atoms
They contain.
The triose C3H6O3 ..….C3(H2O)3
The tetrose C4H8O4 ..….C4(H2O)4
The pentose C5H10O5 ……C5(H2O)5
The hexose C6H12O6 ……C6(H2O)6
The heptose C7H14O7 ……C7(H2O)7
The most commonly described types are :
Trioses, pentoses and hexoses.
9. Trioses are important metabolites. They are formed in
the processes of respiration and photosynthesis.
10. Pentose contains 5 carbon atoms (C5H10O5),
As ribose and ribulose.
I
It is used in
Making RNA,
Ribonucleic acid.
Its phosphate,
Ribulose biphosphate, RuBP,
Is important in photosynthesis.
11. Structural isomers of hexose (C6H12O6).
Hexoses are always the compounds that provide
Immediate energy to the cells.
12. Physical property of monosaccharides.
(1) Monosaccharides are easily soluble in water
and give a sweet taste.
(2) After dissolving in water,
monosaccharides can move across the
plasma membrane of the cell.
(Or it it said that there is carrier enzyme on
plasma membrane that can carry monosaccharides
across the plasma membrane.)
(3) After dissolving in water, monosaccharide
would lower the water potential of the
water body.
13. (4) After dropped into water,
monosaccharides would coil up to form
pentagon rings or hexagon rings.
If it is a pentagonal ring,
It is said to be resemble the structure of a furan.
Then, the sugar is called a furanose.
If it is a hexagonal ring,
It is said to be resemble the structure of a pyran.
Then, the sugar is called a pyranose.
14. (5) Optical activity (an optional property)
Optical activity describes
whether the water solution of a compound
Can rotate the plane of polarized light.
If the water solution of a compound
Can rotate the plane of polarized light,
It is said to be optical active.
Otherwise, it is optical inactive.
15. Chemical property of monosaccharides.
The most important chemical property
Of monosaccharides is the
Reducing power.
16. The standard of the reducing power of carbohydrate
Is the power to reduce copper (II) ion (Cu2+)
In alkaline solution into the Cu2O brick-red precipitate.
If a sugar can do this,
It is said to be a reducing sugar.
If it cannot,
It is said to be a non-reducing sugar
All monosaccharides are reducing sugar.
Benedict’s Test and Fehling’s Test are tests
applying this concept.
18. In the process, one molecule of water is removed.
So, the reaction is called a condensation reaction.
The chemical bond formed is called a
Glycosidic bond (linkage).
19. Physical property of disaccharides.
(1) Disaccharides are easily soluble in water
and give a sweet taste.
(2) After dissolving in water,
disaccharides cannot move across the
plasma membrane of the cell.
(Or it it said that there is no carrier enzyme on
plasma membrane that can carry disaccharides
across the plasma membrane.)
(3) After dissolving in water, disaccharide
would lower the water potential of the
water body.
(4) Also, all disaccharides are optical active.
20. Chemical property of disaccharides.
In maltose and lactose, there is still
One alcohol group attaching the 1st carbon
Not engaged in the formation of glycosidic bond.
It is reductable.
So, they are still reducing sugars.
In sucrose, both reductable alcohol groups
Are involved in the formation of glycosidic bond.
So, it is a non-reducing sugar.
21. The decomposition of disaccharides into monosaccharides
Is called hydrolysis,
Because one molecule of water should be added.
22. The polymers of monosaccharides
Are polysaccharides,
As starch, glycogen, cellulose and amylose
Are polymers of glucose.
They all are polysaccharides.
23. Physical property of polysaccharides.
(1) Polysaccharides are insoluble in water
and cannot give any taste.
(2) As it cannot be dissolved in water,
polysaccharides cannot move across the
plasma membrane of the cell and
cannot change the water potential of the
water body.
(3) No optical activity can be observed.
24. Disaccharides and polysaccharides always serve as the
Energy stores.
Few organisms would store disaccharides inside bodies,
Because disaccharides would cause some water problems.
Only sugar cane and sugar beet would store sucrose.
Starch is stored in plants, while glycogen is stored in animals.
