1.2 Carbohydrates

What are monosaccharides? Give 3 common examples

● Monomers from which larger carbohydrates are made

● Glucose, fructose, galactose

Describe the structure of α-glucose

Describe the difference between the structure of α-glucose and β-glucose

OH group is below carbon 1 in α-glucose but above carbon 1 in β-glucose

Define an isomer and give an example

Molecules with the same molecular formula, differently arranged atoms.

Alpha and beta glucose are isomers.

What are disaccharides and how are they formed?

● Two monosaccharides joined together with a glycosidic bond

● Formed by a condensation reaction, releasing a water molecule

List 3 common disaccharides & monosaccharides from which they’re made

Maltose = Glucose + glucose

Sucrose = Glucose + fructose

Lactose = Glucose + galactose

Draw a diagram to show how two monosaccharides are joined together

What are polysaccharides and how are they formed?

● Many monosaccharides joined together with glycosidic bonds

● Formed by many condensation reactions, releasing water molecules

Describe the basic function and structure of starch

Energy store in plant cells

● Polysaccharide of α-glucose

● Amylose - 1,4-glycosidic bonds → unbranched

● Amylopectin - 1,4- and 1,6-glycosidic bonds → branched

Describe the basic function and structure of glycogen

Energy store in animal cells

● Polysaccharide made of α-glucose

● 1,4- and 1,6-glycosidic bonds → branched

Explain how the structure of starch relates to its function (amylose)

● Helical → compact for storage in cell

● Large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane

● Insoluble in water → water potential of cell not affected (no osmotic effect)

Explain how the structure of glycogen related to its function (and starch amylopectin)

● Branched → compact / fit more molecules in small area

● Branched → more ends for faster hydrolysis → release glucose for respiration to

make ATP for energy release

● Large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane

● Insoluble in water → water potential of cell not affected (no osmotic effect)

Describe the basic function and structure of cellulose

Provides strength and structural support to plant / algal cell walls

● Polysaccharide of β-glucose

● 1,4-glycosidic bond → straight, unbranched chains

● Chains linked in parallel by hydrogen bonds forming microfibrils

Explain how the structure of cellulose relates to its function

● Every other β-glucose molecule is inverted in a

long, straight, unbranched chain

● Many hydrogen bonds link parallel strands

(crosslinks) to form microfibrils (strong fibres)

● Hydrogen bonds are strong in high numbers

● So provides strength to plant cell walls