Carbohydrate
January 1999
B io Factsheet
Example glucose fructose galactose
Number 39
Carbohydrates: Revision Summary
Carbohydrates contain 3 elements: Carbon (C), Hydrogen (H) and Oxygen (O). Thus, if we remove water from carbohydrates, all that remains is carbon. Carbohydrates can be divided into 3 categories; monosaccharides, disaccharides and polysaccharides (Table 1).
Table 1. Structure of monosaccharides, disaccharides and polysaccharides Category Monosaccharide (made of 1 sugar molecule)
Site fruit fruit, nectar milk
H
Structure
OH
OH
H
α-glucose Disaccharide (made of 2 monosaccharides joined together) Polysaccharide (made of many monosaccharides joined together) maltose = α-glucose + α-glucose sucrose = glucose + fructose lactose = glucose + galactose germinating seeds phloem tissue, fruit milk
β-glucose
fructose
O
maltose starch glycogen cellulose chitin = = = = polymer of glucose polymer of α-glucose polymer of β-glucose polymer of glucosamine (glucose with an amino acid attached) chloroplast stroma muscle cells plant cell wall exoskelteton of arthropods
O O
O O
cellulose
Monosaccharides and Disaccharides
Monosaccharides and disaccharides are sugars. They all have the basic formula (CH2O)n and can be classified according to how many carbon atoms they contain. 3C = triose sugars e.g. glyceraldehyde C3H5O2 5C = pentose sugars e.g. ribose C5H10O5 6C = hexose sugars e.g. glucose C6H12O6
Formation of disaccharides - typical exam questions
Common exam questions include: 1. Name the reaction involved when a disaccharide is formed 2. Name the type of bond formed 3. Show, by drawing a diagram, how a disaccharide is formed Questions 1 and 2 are very simple - Disaccharides form in a condensation reaction which forms a glycosidic bond. The only way to get Question 3 correct is to practice! Fig 1 shows how maltose and sucrose are formed from their monosaccharides.
Fig 1. Formation of maltose and sucrose from their
B io Factsheet
Example glucose fructose galactose
Number 39
Carbohydrates: Revision Summary
Carbohydrates contain 3 elements: Carbon (C), Hydrogen (H) and Oxygen (O). Thus, if we remove water from carbohydrates, all that remains is carbon. Carbohydrates can be divided into 3 categories; monosaccharides, disaccharides and polysaccharides (Table 1).
Table 1. Structure of monosaccharides, disaccharides and polysaccharides Category Monosaccharide (made of 1 sugar molecule)
Site fruit fruit, nectar milk
H
Structure
OH
OH
H
α-glucose Disaccharide (made of 2 monosaccharides joined together) Polysaccharide (made of many monosaccharides joined together) maltose = α-glucose + α-glucose sucrose = glucose + fructose lactose = glucose + galactose germinating seeds phloem tissue, fruit milk
β-glucose
fructose
O
maltose starch glycogen cellulose chitin = = = = polymer of glucose polymer of α-glucose polymer of β-glucose polymer of glucosamine (glucose with an amino acid attached) chloroplast stroma muscle cells plant cell wall exoskelteton of arthropods
O O
O O
cellulose
Monosaccharides and Disaccharides
Monosaccharides and disaccharides are sugars. They all have the basic formula (CH2O)n and can be classified according to how many carbon atoms they contain. 3C = triose sugars e.g. glyceraldehyde C3H5O2 5C = pentose sugars e.g. ribose C5H10O5 6C = hexose sugars e.g. glucose C6H12O6
Formation of disaccharides - typical exam questions
Common exam questions include: 1. Name the reaction involved when a disaccharide is formed 2. Name the type of bond formed 3. Show, by drawing a diagram, how a disaccharide is formed Questions 1 and 2 are very simple - Disaccharides form in a condensation reaction which forms a glycosidic bond. The only way to get Question 3 correct is to practice! Fig 1 shows how maltose and sucrose are formed from their monosaccharides.
Fig 1. Formation of maltose and sucrose from their