AQA A-level Biology Summary Notes
Carbohydrates (Saccharides)
Glucose
Glucose is a hexose sugar (it has 6 carbons).
There are two forms of glucose, Alpha (α) glucose and Beta (β) glucose.
This is the complex structure of α-glucose, for the exam you only need to know the simplified
version for your exams.
In comparison, this is the structure of β-glucose, which only has one difference. There is an
OH group next to the oxygen instead of an H.
Monosaccharides
Have a general formula of (CH2O)n where n is any number from 2 to 7.
Are sweet soluble crystals
E.g.
o Glucose (both forms)
o Fructose (found in fruit)
o Galactose
Disaccharides
Disaccharides are formed when two monosaccharides are joined by a glycosidic bond in a
condensation reaction (water is produced as a bi-product)
One monosaccharide will lose a hydrogen atom, while the other loses an OH (hydroxide) group to
form water
This can be reversed in a hydrolysis reaction to form two monosaccharides (water required)
Carbohydrates (Saccharides)
Glucose
Glucose is a hexose sugar (it has 6 carbons).
There are two forms of glucose, Alpha (α) glucose and Beta (β) glucose.
This is the complex structure of α-glucose, for the exam you only need to know the simplified
version for your exams.
In comparison, this is the structure of β-glucose, which only has one difference. There is an
OH group next to the oxygen instead of an H.
Monosaccharides
Have a general formula of (CH2O)n where n is any number from 2 to 7.
Are sweet soluble crystals
E.g.
o Glucose (both forms)
o Fructose (found in fruit)
o Galactose
Disaccharides
Disaccharides are formed when two monosaccharides are joined by a glycosidic bond in a
condensation reaction (water is produced as a bi-product)
One monosaccharide will lose a hydrogen atom, while the other loses an OH (hydroxide) group to
form water
This can be reversed in a hydrolysis reaction to form two monosaccharides (water required)
