Carbohydrates

Monosaccharides

- simple sugars which cannot be broken down into other sugars. They are categorized according to the number of carbon atoms.

• Triose – a three (3) carbon sugars which is produced from the breakdown of hexoses.
• Tetroses – a four (4) carbon sugar. One example is erythrose which is an intermediate of hexose monophosphate shunt for the oxidation of glucose.
• Pentoses – are five (5) carbon sugar. The most important examples are ribose and deoxyribose which are found in nucleic acid. Ribose form part of the ribonucleic acid (RNA) and deoxyribose in deoxyribonucleic acid (DNA) which are components of every cell nucleus and cytoplasm
• Hexoses – a six (6) carbon sugar. Examples are glucose, galactose and fructose with the same molecular formula but differ in structures (isomers).

1. Glucose

- aldohexose

- It is commonly known as dextrose or a grape sugar

- It is a white crystalline solid that is soluble in water but insoluble in organic liquids.

- It is found in the human bloodstream and tissue fluids.

- It requires no digestion and can be given intravenously to patients who are unable to take food by mouth.

• Glycosuria – is a condition where glucose can be found in the urine.

2. Galactose

- aldohexose

- It differ from glucose in the structure (epimer)

- D-galactose is converted to glucose in the liver by the enzyme epimerase

• Galactosemia – a severe inherited disease, results in the inability of infants to metabolize galactose because of the deficiency of enzyme galactokinase.
• Galactosuria – a condition where increase of galactose in the urine.

3. Fructose

- ketohexose

- also known as levulose or a fruit sugar

- It occurs naturally in fruit juices and honey. It is sweeter than glucose.

- It is prepared by the hydrolysis of sucrose and inulin.

• Fructosemia – fructose intolerance, an inherited disease due to the deficiency of enzyme fructose 1-phosphate aldolase. An infant suffering from the disease experiences hypoglycemia, vomiting and severe malnutrition. Such condition is treated to a low- fructose diet.

Disaccharides

1. Sucrose

- or cane sugar,  sugar ordinarily used at home

- produced commercially from sugar cane and sugar beets

- occurs in sorghum, pineapple and in carrots roots

- When hydrolyzed, it forms glucose and fructose.

- Invert sugar is a 50-50 mixture of glucose and fructose. Honey contains a high percent of invert sugar.

- will ferment with yeast due to the presence of the enzyme sucrase

2. Maltose

- commonly known as malt sugar, is present in germinating grain

- produced commercially from the hydrolysis of starch

- will ferment with yeast due to the presence of the enzyme maltase

3. Lactose

- commonly known as milk sugar, is present in milk

- differs from the preceding sugars in that it has an animal origin

- Certain bacteria cause lactose to ferment, forming lactic acid. When reaction occurs, the milk becomes sour.

- Lactose is used in high calcium diets and in infant foods.

- Lactose can be found in the urine of pregnant women.

- will not ferment with yeast because of the absence of the enzyme lactase

Polysaccharides

• are polymers of monosaccharides

• Complete hydrolysis of polysaccharides produces many molecules of monosaccharides.

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1. Starch

- a mixture of polysaccharides amylopectin and amylose. Amylopectin is a branched polysaccharide in starch in large amount (80-85%) while amylose is a nonbranched polysaccharide(15-20%).

- insoluble in water.

- iodine test: deep blue color.

2. Cellulose

- wood, cotton and paper composed primarily of cellulose

- It is the supporting and structural substance of plants.

- a polysaccharide composed of many glucose units

- It is not affected by any enzyme in the human digestive system and it cannot be digested.

- When eaten with other foods, it gave a bulk to the feces and prevents constipation.

- it does not dissolve in water and in most ordinary solvents

- iodine test: no color

3. Glycogen

- is present in the body and is stored in the liver and muscle, where it serve as a reserve supply for glucose

- is of animal origin

- forms a colloidal dispersion with water

- iodine test: red color

• Glycogenesis - is a process where glycogen is formed in the body cells from the molecules of glucose.

  glucose >>> glycogen

• Glycogenolysis - is a process when glycogen is hydrolyzed into glucose.

  glycogen >>> glucose

4. Dextrin

- produced during the hydrolysis of starch

- It is an intermediate between starch and maltose.

-  is used in the preparation of adhesives

- The glue at the back of a postage stamp is dextrin.

- Dextrin is used when digestion of starch is a problem with infants and elderly persons.

- forms sticky colloidal suspension with water

5. Heparin

- is a polysaccharide used as blood anti-coagulant

- It is the strongest organic acid present in the human body.

6. Dextran

- is a polysaccharide produced from certain bacteria when they are grown  on sucrose

- used as blood extenders to hold water in the bloodstream and helps prevent drop in blood volume and blood pressure

- Dextrans growing on the surface of the teeth are important component of dental plaque.

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