True colour polarized light image of glucose.

Scanning electron microscopy image of glucose.Transmission electron microscopy image of glycogen (G) in spermatozoa of a flatworm.

Light microscopy. Cellulose of corn stained purple with Toluidine blue.

Learning objectives:

• Introduction to saccharide.

• Type of monosaccharide and their importance.

• Glucose, fructose, galactose as important hexose.

1.3 Saccharide

Saccharide 糖类• Originated from the Greek word

σάκχαρον (sákkharon), meaning "sugar“

• Abundant 大量 organic compound in organisms

• Contains carbon (C), hydrogen (H) and oxygen (O) atoms

• hydrogen–oxygen atom ratio of 2:1

• empirical formula 经验分子式 Cm(H2O)n, except for deoxyribose etc.

• major source of fuel for metabolism • Energy source

• Biosynthesis

Saccharide a.k.a. carbohydrate.

Classification of saccharidename of monosaccharide and disaccharide ends with a suffix -ose, Latin adjective-forming suffix -ōsus = "full of", "abounding in".

单糖 双糖 多糖

Table 1.1 Classification of saccharides

Categories Examples Distributions Main functions

Monosaccharide

Glucose Fruits, blood Can be used directly in

metabolism; produce energyFructose Fruits, honey

Galactose Formed by digested lactose

Ribose Composition of nucleotide

Disaccharide

Sucrose Beets and sugar canes

contain the most

Can dissolve in water;

easily for hydrolysis and

transportation Maltose Does not exist free in nature,

product of hydrolysis of

starch

Lactose Milk of mammals

Polysaccharide

Starch Product of photosynthesis of

green plants

Store energy;

form cell walls and others

structuresGlycogen Animals’ livers and muscles

Cellulose Composition of plants’ cell

walls and leaf tissues

1.3.1 Monosaccharide

Monosaccharide 单糖

• The most simple sugar – cannot be hydrolyzed

• Used directly in metabolism

• Oxidized to produce energy

• Readily soluble in water – suitable for transportation

• Empirical formula (CH2O)n, n = 3, 5, 6 (as far as we concern)

• Can be grouped by the number of carbon in a monosaccharide• triose, pentose, hexose

IUPAC numerical multiplier

Number Multiplier

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

11 undeca-

Quiz

• Formula for monosaccharide is

a. (CH2O)n.

b. CnH2n.

c. both A and B.

d. none of above.

Glyceraldehyde (glyceral)

Triose 3C

Hexose 6C

Pentose 5C

脱氧核糖核糖甘油醛

葡萄糖 果糖 半乳糖

糖蜜

Example of food source for hexose

Importance of monosaccharideSaccharide Example Source Importance

Triose Glyceraldehyde Intermediate between photosynthesisand glycolysis 糖酵解 process

Essential in importantmetabolism of organism

Pentose Deoxyribose Oxyribose

DNA (stores biological information)RNA (use for protein transcription)

Important component of nucleic acid

Hexose GlucoseFructose Galactose

Store in fruits, honey, bloodStore in fruits, honey, bloodProduce of lactose hydrolysis

Primary energy source

Quiz

• Units of carbohydrates which cannot be further hydrolyzed to simpler compounds are

a. disaccharides.

b. polysaccharides.

c. monosaccharides.

d. none of above.

Quiz

• Picture on the left shows a

a. Triose

b. Pentose

c. Hexose

Conclusion

• Saccharides are organic compounds that function as the main energy source in the cells.

• Saccharides can be classified as monosaccharide, disaccharide, and polysaccharide based on the their molecular weight.

• Monosaccharides can be classified based on the number of carbon atoms they contain, i.e. triose (3C), pentose (5C) and hexose (6C).

• Glucose, fructose and galactose are important hexose that can we obtain from food.

• Ribose and deoxyribose are pentose that forms RNA and DNA.

• Glyceraldehyde are important intermediates for cellular respiration (conversion of nutrient to energy) and photosynthesis.

Differential interference contrast microscopy picture of fructose crystal. 100x

Scanning electron microscope: (A) lactose 100M at 1200×, (B) lactose 200M at 1200×.

Presence of reducing sugars can be detected with Benedict’s solution.

Quiz

• Saccharides contain the following combination of elements:

a. carbon, hydrogen and phosphorus

b. carbon, nitrogen and hydrogen

c. carbon and hydrogen

d. carbon, oxygen and hydrogen

Glucose molecule exists in both linear and ring forms.

1.3.2 Disaccharide

Learning objectives

• General structure of disaccharides

• Monomers of disaccharides

• Condensation and hydrolysis reactions

• Reducing sugars and Benedict’s test

Disaccharide 双糖

• Compound with two identical or different monosaccharides

• Condensation 缩合反应 of two monosaccharides gives a disaccharide

• Hydrolysis 水解反应 of a disaccharide provides two monosaccharides

• Formula C12H22O11

蔗糖

乳糖

麦芽糖

Example of food source for disaccharides

Corn

(lactose)

Sugar beet / Sugar cane (maltose)

Hydrolyses of starch(sucrose)

Diary products

Condensation reaction 缩合反应

• Two or more molecules combine

• lose a small molecule, generally water

Mnemonics 助忆:GGM: Go Grand Ma! GFS: Go Father Son! GGL: Go Good Luck!

Hydrolysis reaction 水解反应

• Greek – hydro: water, lysis: break

• Polymers disassemble into respective monomers

• Addition of a water molecule to break a bond

• Disaccharide can be broken down into monosaccharides when being treated with acid 酸, heat 热 or enzyme 酶

• The saccharide known as milk sugar is also known by the common name:

a. Sucroseb. Fructosec. Lactosed. Maltose

Quiz

• The saccharide known as milk sugar is also known by the common name:

a. Sucroseb. Fructosec. Lactosed. Maltose

Quiz

• What is the unknown saccharide shown above?

a. Galactose

b. Lactose

c. Maltose

d. Sucrose

e. Cellobiose

Reducing sugars

Redox reaction • Reduction–oxidation reaction = two reactions occurs simultaneously

• Process where oxidation states of atoms are changed, i.e. the number of electrons are changed in this reaction

• Release energy when electrons are relocated

• The handwave version of what happens:

Oxidation 氧化

• Gain of oxygen, loss of hydrogen, or loss of electron

Reduction 还原

• Loss of oxygen, gain of hydrogen, or gain of electron

Reduce of charge

Reducing agents and oxidizing agents

• Reducing agents 还原剂cause others to reduce

• Reducing agents themselves undergo oxidation

• Oxidizing agents 氧化剂cause others to oxidize

• Oxidizing agents themselves undergo reduction

Reducing sugar 还原糖 as reducing agent

• Important in energy production

• Contain a free aldehyde group or a free ketone group

• The aldehyde or ketone group donates electron(s)

• Oxidation occurs on the oxygen atom

• All monosaccharides and many disaccharides except sucrose are reducing sugar

Glyceraldehyde

free aldehyde group

free ketone group

Fructose

Why sucrose is not a reducing sugar

• In monosaccharides and disaccharides, although a ring structure is generally favours by chemical equilibrium, sometimes the saccharides can exists in linear form, exposing the free aldehyde or ketone group.

• Due to how glucose and fructose are linked in sucrose, sucrose does not have a linear form.

Glucose molecule exists in both linear and ring forms.

Benedict’s test for reducing sugar• Benedict’s solution is used to determine the reducing capability by

determine the presence of free aldehyde or ketone group in sugars.

• Copper(II) sulphate (CuSO4) is reduced by the reducing sugars.

• Copper (I) oxide (Cu2O) is the resulting precipitate.

Cu2+

BlueClear

OH-

Cu+

Brick RedPrecipitate

Differential interference contrast microscopy picture of fructose crystal. 100x

Scanning electron microscope: (A) lactose 100M at 1200×, (B) lactose 200M at 1200×.

Presence of reducing sugars can be detected with Benedict’s solution.

Conclusion• Disaccharides are synthesized by condensation of two monosaccharides

• Hydrolysis of disaccharides produces monosaccharides.

• Examples of disaccharides:• Maltose (glucose + glucose)

• Sucrose (glucose + fructose)

• Lactose (glucose + galactose)

• All monosaccharides and many disaccharides except sucrose are reducing sugars.

• Benedict’s test detects the presence of reducing sugars.

Cu2+

BlueClear

OH-

Cu+

Brick RedPrecipitated

Quiz

• If you mixed Benedict's solution with a small amount of tea and placed it in a hot water bath for 5 minutes, then checked the colour, which of these colors would NOT indicate that the tea contained sugars?

a. Blue

b. Green

c. Yellow

d. Brownish red

e. Orange

Quiz

• Figure on the left shows the result of a quantitative test of the amount of reducing sugar in a solution. What the percent solution the unknown (right most test tube)?

a. 0.05%

b. 0.10%

c. 0.25%

d. 0.5%

e. 1.00%

Quiz

• The general formula for a disaccharide is

a. C3H6O3

b. C12H22O11

c. C6H12O6

d. C12H24O12

Starch grains in Ranunculus are stained purple with iodine.

Glycogen granules in beef muscle cell under electron microscope.

Lower stem of water plant Myriophyllum sp. under ultraviolet light with cellulose stained with fluorochorome calcoflour.

xylemair channels (aerenchyma) phloem pith

Quiz

• Which two monosaccharides combine to form sucrose?

a. Glucose + Fructose

b. Glucose + Glucose

c. Glucose + Galactose

d. Glucose + Maltose

e. Fructose + Galactose

1.3.3 Polysaccharide

Polysaccharide 多糖• Most abundant sugar in nature

• Formed by condensation of monosaccharides (generally glucose)

• May be branching 分支 or not branching 分支 long chain 长链分子

• Insoluble in water, tasteless, uncrystallize 不结晶, non-reducing

• Important as energy storage and structural molecules

• Empirical formula (C6H10O5)nCellulose is made up from a long chain of glucose.

Example of polysaccharide

Starch grain of different commercial crops.

Starch 淀粉• Glucose storage in plant

• Two type：• Amylose 直链淀粉

• Amylopectin 支链淀粉

• The ratio of amylose to amylopectin varies

• Stored in seed, tubers, roots

Glycogen 糖元/肝糖• Glucose storage in animal (liver,

muscle), some bacteria

• A.k.a animal starch

• Glycogen branches more than amylopectin

• Release energy faster – more active site 活性位点 for reaction

• Liver glucogen maintains blood glucose level.

• Muscle glycogen supplies energy for muscle contraction.

Cellulose

• Primary component of plant cell wall

• Most common sugar

• Similar with amylose, but different kind of bonds

Rayon made from cellulose extracted from bamboo.

Different type of covalent bonds in amylose and cellulose.

Quiz• John ran out of glutinous rice flour, which is important to make sticky

sweet rice ball. He somehow still remember the amylose contain of the flours that he owned. If he must add other kind of flour into his glutinous rice flour mix, what is his best choice?

a. Green bean flour

b. Corn flour

c. Potato flour

Type of Flour Amylose contain (%)

Glutinous rice 5%

Green bean 92%

Corn flour 27%

Potato flour 20%

Quiz

• Which of these carbohydrates is NOT digestible and provides fiber, or "roughage" in humans?

a. sucrose

b. starch

c. glycogen

d. cellulose

e. lactose

Quiz

• Starch is a polymer made from the following monomer:

a. Glucose

b. Fructose

c. Galactose

Conclusion• Formed by condensation of monosaccharides (generally glucose)

• Insoluble in water, tasteless, uncrystallize, non-reducing

• Important as energy storage and structural molecules

(plant) (plant)(animal)

Quiz

• Which are long chain structures that are constructed by glucose?

I Cellulose

II Glycogen

III Maltose

IV Starch

A. I, II, III

B. II, III, IV

C. I, II, IV

D. I, II, III, IV

Quiz

• Which of the following combinations of statements is true of polysaccharides in living organisms?

They provide They form They form

energy storage supporting

compounds structures

A No No Yes

B Yes No No

C Yes Yes No

D Yes Yes Yes

Short answer questions

(1) What is the difference of glycogen and cellulose?

(2) Explain the hydrolysis reaction of starch.

Sample answer:

1. The glucose monomers of glycogen are bonded in a similar fashion to amylopectin, i.e. with many side chains; while the glucose monomers of cellulose are bonded together without side chains, which is similar to amylose.

2. In the presence of water and enzyme, starch can be hydrolysed into maltose. Maltose can be further hydrolysed into glucose.

Quiz

• The type of reaction that occurs when a disaccharide is formed from two monosaccharides is

a. condensation

b. addition

c. hydrolysis

d. reduction

Quiz

• Polysaccharides

a. include glycogen, cellulose, and starch.

b. consist of many glucose molecules bound together in long chains.

c. can be energy storage molecules.

d. all of these

Quiz

All of these carbohydrates come from plants EXCEPT:

a. cellulose.

b. fructose.

c. lactose.

d. maltose.

e. sucrose.

Quiz

• The polysaccharide used for energy storage in the human body is

a. cellulose.

b. glycogen.

c. lactose.

d. sucrose.

e. starch.