02: Sugars and Polysaccharides

Define a monosaccharide and give an example

A single sugar unit, e.g. glucose, fructose, galactose, mannose

Define a disaccharide, and give an example

Two monosaccharides joined together by a glycosidic bond, e.g. lactose (glu-gal), maltose (glu-glu), and sucrose (glu-fru)

Define an oligosaccharide, and give an example

3-10 monosaccharides joined together by glycosidic bonds, e.g. raffinose (gal-glu-fru), heparin, fructooligosaccharides, galactooligosaccharides, blood group antigens

Define a polysaccharide, and give an example

More than 10 monosaccharides linked together by glycosidic bonds, e.g. glycogen (a-1,4) and cellulose (b-1,4)

Main purpose of monosaccharides?

For energy

Main purpose of disaccharides?

For transport

Main purpose of polysaccharides?

For storage

What makes monosaccharides different from each other?

• number of carbon atoms (3,4,5,6, or 7 - triose, tetrose, pentose, hexose or heptose)

• whether they are aldehydes or ketones (depends on position of C=O group)

Define an asymmetric carbon

A carbon in a molecule with covalent bonds to 4 different groups

Define enantiomers

Pair of isomers that are non-superimposable mirror images

What is meant by D- and L- forms of a monosaccharide? And what happens if there is more than 1 chiral carbon?

• Applies to monosaccharides with 1+ asymmetric carbon atoms

• D- form: -OH group is attached to right of asymmetric carbon

• L- form: -OH group is attached to left of asymmetric carbon

• If there is more than 1 chiral C, look at the chiral carbon furthest from C=O group to determine D or L form

Which form of enantiomer is more common?

D

Define glycosidic bond, and give an example

A covalent bond that joins a sugar molecule to another group formed via a condensation reaction where water is lost, e.g. alpha-1,4 glycosidic bond

Define sugar esterification, and give an example

The addition of phosphate/sulphate groups to a monosaccharide’s hydroxyl (-OH) group, e.g. glucose-6-phosphate (in glycolysis) or chondriotin sulphate

Define an amino sugar, and give an example

A monosaccharide where the -OH group is replaced with an amino group (-NH2 group), e.g. glucosamine (in cartilage)

Define a deoxy sugar, and give an example

A monosaccharide where an -OH group is replaced with an -H atom, e.g. deoxyribose (in DNA)

What are the two groups of carbohydrates?

Simple and complex carbohydrates

What is the ratio of C, H and O atoms in carbohydrates?

1:2:1