Biomolecules

Lesson

Part 1 — carbohydrates: the sugars and starches that fuel living things.

In this lesson you will

Classify carbohydrates as monosaccharides, oligosaccharides and polysaccharides, and as reducing or non-reducing sugars
Describe the preparation and open-chain structure of glucose and the evidence for it
Explain the cyclic structures of glucose and fructose and the idea of anomers
Describe sucrose, maltose, lactose, starch, cellulose and glycogen and the importance of carbohydrates

Table of the main classes of biomolecules with examples
Biomolecule	Example in your body or food
Carbohydrates	Rice starch, cane sugar, glycogen in liver
Proteins	Muscle, keratin in hair, enzymes
Nucleic acids	DNA in chromosomes
Vitamins	Vitamin C in amla and citrus fruits
Hormones	Insulin, adrenaline

Concept

Classifying carbohydrates

Carbohydrates are polyhydroxy aldehydes or ketones, or compounds that give them on hydrolysis. Monosaccharides cannot be hydrolysed further; oligosaccharides give 2–10 monosaccharide units; polysaccharides give many. Sugars that reduce Tollens’ or Fehling’s reagent are reducing sugars.

Table classifying carbohydrates with examples, hydrolysis products and whether they are reducing
Class	Example	Hydrolysis products	Reducing?
Monosaccharide (aldose)	Glucose	None	Yes
Monosaccharide (ketose)	Fructose	None	Yes
Disaccharide	Sucrose	Glucose + fructose	No
Disaccharide	Maltose	2 glucose	Yes
Disaccharide	Lactose	Galactose + glucose	Yes
Polysaccharide	Starch, cellulose	Many glucose	No

Concept

Aldoses and ketoses

Monosaccharides are named by the carbonyl group and the number of carbons: an aldohexose has an aldehyde group and six carbons (glucose); a ketohexose has a ketone group and six carbons (fructose).

Table of aldoses and ketoses with three, five and six carbon atoms and examples
Carbon atoms	Aldose	Ketose
3	Aldotriose (glyceraldehyde)	Ketotriose
5	Aldopentose (ribose)	Ketopentose
6	Aldohexose (glucose, galactose)	Ketohexose (fructose)

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